Why Preppers Need a 3D Printer: Repairing the clothes dryer


We are writing this post for our “prepper friends“: Folks who like to be able to take care of themselves even if some catastrophic event cripples their communities infrastructure.

We assume the reader of this article has no expertise with:

  • Designing 3D Models
  • Using a 3D Printer to print objects

Like most technologies creating objects with 3D Printers varies from simple to complex.

Do you need to know a lot about your cell phone to use it?

Yet, your cell phone has more computational power then all five of the computers used on the first space shuttle combined!

You might not be able to fly a space shuttle but you know how to share your latest picture / video / insights with an entire planet of people with a few “clicks”.

However, if you want to edit your picture / video before you share them that is also possible but you have to “learn a few things” first.

Anyone is capable of learning how to create ( design and print ) “unique objects” using a 3D Printer.

The overarching objective of this post is to introduce 3D Printing to newbies ( No insult intended: We were “newbies” when we began traveling this path ).

Notes for Preppers:

We believe: You can’t prepare for every contingency by purchasing “things”… Murphy’s Law: Whatever can go wrong will go wrong.

We also believe: You can maximize your preparedness by developing skills ( while recognizing that no single individual will be able to become completely prepared ⇒ “preparing for every contingency” requires a community of diverse skills )

One of the skills that must be achieved: Knowing what to stock!
Sack of Pinto Beans

Sack of Pinto Beans

Refried Beans

Refried Beans

A simple example: Stock cans of re-fried beans or sacks of dried pinto beans?

From a skills perspective: Re-fried beans are easy to make from dried pinto beans if you know how ( “Have the skill” ).

There are more dimensions involved in the “decision process”:

  • Cost: Dried pinto beans are less expensive than cans of re-fried beans
  • Time: Opening a can of re-fried beans requires seconds while making re-fried beans from dried beans requires a day ( soaking for 12 hours / slow boil the beans for 12 hours + 10 – 30 minutes to transform into “re-fried beans” )
  • Ancillary Requirements: A can of re-fried beans requires a can opener ( Optional: heat ) while the dried beans require water, soaking container / boiling container & a prolonged application of heat
  • Shelf life / environment: Cans of re-fried beans will likely last longer in warmer, humid environments
  • Self Replication: Dried beans will sprout & new bean plants may be grown => Impossible to replicate with cans of re-fried beans
  • etc…

Pondering etc… is the source of never ending insight.

From a practical perspective it would be wise to stock both cans of re-fried beans and sacks of dried beans to accommodate real-world circumstances: “Survival” requires both time and energy => After a long day toiling in the field having an easy meal from a can of beans might be critical for completing planting. ( Since calling for Pizza delivery won’t be an option )

Prepping Stocking Trade-offs

Prepping Stocking Trade-offs

If we assign elemental status to “dried beans” it highlights the fact that “re-fried beans” are refined ( derived ) from “dried beans” and represents only one of the possible refined goods that could be made from “dried beans”.

It’s when we take the elemental / refined concept and apply it to tools / machines / durable goods while considering repair / maintenance that we gain tremendous insight into answering the question What items should we stock?

If we stock elemental materials we require less diversity in our inventory but we need more skills.

This diversity / skills trade-off fact was once “common knowledge”. However, when you ask a young person Where does food come from? and the answer is The supermarket. it is safe to assume that we might not be stating the obvious for everyone.

3D Printers reduce “skill set” requirements while increasing object diversity

Our claim that a 3D Printer will reduce skill set requirements and promote object diversity is our foundation supporting our recommendation to preppers to acquire a 3D Printer and associated skill set.

We prove our argument through examples => Fix the Dryer is one data set. ( An empirical proof ).

It is a good to be skeptical of our claim: Sounds a bit like magic.

A 3D Printer is a robot that is programed by creating a 3D Model of the object you want to create.

Full Disclosure: It’s a tad more complicated => The 3D Model is fed into a “3D Model Slicing Tool” which creates the “machine code” for the 3D Printer.

“Slicing Tools” have lots of settings / variables to control how the transformation of the 3D Model into 3D Printer machine code is implemented => Skills / Magic

Bottom Line:

  • Learning how to use a 3D Printer will allow the creation of greater object diversity then learning how to operate a mill ( or any other singular tool / machine )
  • Purchasing a 3D Printer is less expensive then purchasing the CNC Mill + CNC Drill + CNC Lathe + CNC Saw that the 3D Printer effectively replaces

We followed the traditional path:

  • Acquired wood working tools & developed the necessary skills for each machine
  • Acquired metal working tools & developed the necessary skills for each machine
  • Acquired CNC wood working router & learned how to use it ( turned out to be a waste of time and money due to the low quality we were able to afford )
  • Acquired pottery tools & developed the necessary skills for creating objects using clay slabs ( We have a long way to go to explore all of the methods available to work with clay… )
  • Acquired the equipment necessary to build and test Printed Circuit Boards ( Now we are able to 3D Print Printed Circuit Boards )
  • Acquired a 3D Printer & learned how to use it

If you have been following the same / similar path then adding a 3D Printer to your shop is a natural & smart “next step”

Our conclusion: Every prepper community should have a 3D Printer ( or two… or three… ) and at least one person who knows how to design 3D Models for the 3D Printer and at least one person who knows how to tune & maintain / repair your 3D Printer.

It would be really great if you had local access to one person who could perform both tasks: 3D Model Design and 3D Printer tuning / maintenance & repair

Fused Filament 3D Printers are complex machines that experience high G forces & high vibration forces while needing to maintain high accuracy across “high” resolution ( ~0.0004 in = 0.4 mils | 0.01 mm ) ⇒ Maintenance is a routine task.

This post describes a practical application: How to fix your clothes dryer by using “common parts” ( like ball bearings ) and making your own replacement part.

We hope: by reading this post you will understand that you too could design and create any object that you might need.

Sometimes you might need to be “creative” to achieve the any object goal.

In the past we have:

  • 3D Printed a “master object” that we then used to create an aluminum sand casting
  • 3D Printed a “negative object” ( A.K.A.: “mold” ) that we then filled with silicon to create valve diaphragms
  • 3D Printed a “cookie cutter” ( another form of a “mold” ) that we then used to “stamp out” clay objects from a clay slab ( which we then fired in a kiln ) to create high temperature support structures
    • While we have not 3D Printed a “cookie cutter” for making “cookies” we certainly could…

There are 3D Printers that will print in clay or metal.

  • The metal 3D Printers tend to be “industrial” ( expensive )
  • We could have printed the clay objects using “clay filament” but we stock 25 lb blocks of clay and do not stock clay filament: We used what we had available

3D Printer Technologies

Fused Filament 3D Printer: Extruding Plastic

There are many types of 3D Printers ( 3D Printing Technologies ), some 3D Printers are capable of using more than one 3D Printing technology and there are machines that combine 3D Printing with traditional subtractive technologies ( milling, drilling, etc… ).

We are focused on low-cost, professional grade fused filament 3D Printing technology: A.K.A. Fused Deposition Modeling ( FDM )

Today, everyone has access to most 3D Printer technologies through 3D Printing Service Bureaus.

In fact, you may have a local 3D Printing Service Bureau ( Support your local community & typically obtain great support ).

If you are North-East of Denver, Co in the Bennett / Keenesburg / Roggen / Brighton / Wiggins / Hudson / Watkins / Strasburg / Byers area => Contact us for our 3D printing services

3D.Krakatoa Ranch Local Printing Service Region

3D.Krakatoa Ranch Local Printing Service Region

3D Printing Process Overview

3D Printing Process Overview

Designing and printing an object is composed of three steps:

  1. Creating the 3D Model ( “creating the design” )
  2. Slicing the 3D Model ( transforming the 3D Model into 3D Printer “machine instructions” )
  3. Printing the 3D Model (The fun part: creating the object )

As we work through our “appliance repair example” we will expand upon the three step 3D Printing process.

We use a separate computer for each step in the 3D Printing process ( Not absolutely necessary unless you are processing lots of designs ).

  • The computer ( s ) used for “Creating the 3D Model” and “Slicing the 3D Model” should have lots of RAM and fast processors ( data and computational intensive tasks )
  • The computer used for hosting the 3D Printer driver has minimum hardware requirements ( a low cost { $40$100 } Raspberry PI 3 is sufficient )

We strongly recommend using a ( low-cost ) dedicated computer for the 3D Printer Driver.


Unlike 2D paper inkjet printers where the printer driver operates as a background process a 3D Printer’s driver must run in the foreground ( making that computer useless for other tasks ).

Foreground operation might represent the nascent status of low-cost 3D Printing and will eventually migrate to a background “system services” process…

Thoughts on “Design”:

The subject of this article is replacement part design and implementation using a 3D Printer.

Design is a “massive topic”. When discussing “design” from the perspective of 3D Model creation it is easy to become lost in “tool specific” details, terminology or complexities.

Low Cost 3D Scanner

Low Cost 3D Scanner

Before diving into “design” it is important to highlight another approach: Using a 3D Scanner.

3D Scanning an exiting “object” to create a 3D model for 3D Printing is relatively inexpensive.

3D Scanning requires:

  • An original object in good condition
  • No desire to modify the scanned 3D model ( Possible, but expect to spend some money )

We don’t dive into 3D Scanning in this narrative for two simple reasons:

  • The original “part” was significantly “damaged”
  • We are creating our “replacement part” using standard parts ( ball bearings ) that we have in stock requiring “design changes”

Snow Fort Designer

Snow Fort Designer

Design is the art of identifying and meeting requirements.

An Engineering background is not required but it helps!.

A Person who has obtained an engineering degree but has never designed anything is not a “designer”..

Any kid who has built their own “fort” is a “designer”.

As with any art: experience ( practice ) reigns supreme and persistence is a required trait.

Design: Versions And Implementations

Design: Versions And Implementations

“Design” is an iterative process. Almost always, the first “design” does not work. Why? The design failed to meet all of the requirements ⇒ Usually, because all of the requirements were not recognized ( identified ) prior to creating the “design”.

Designing a “replacement part” is fraught with “unrecognized requirements”. There are obvious requirements: dimensions, function. Then there are the critical but less obvious requirements: Force vectors, operating environment ( temperature ranges, pressure, chemical exposure, etc… ), wear rate, etc…

This post explores “design iterations”. If you are new to design it is easy to become discouraged when your “first design” does not work or fails quickly. Experienced designers know the “first design” isn’t going to work: A good first design will attempt to expose the maximum number of “hidden requirements” ⇒ The “first design” should “work”: but it will fail over a short time period.

Experienced designers “microscopically analyze” design’s “failures” to learn as much as possible.

The “second design” should work for a “longer” period of time before failure. The second design may be the “final design”… Some “designs” never stop iterating: Has the automobile design been perfected or is there a need to continue the evolution?

Simple “replacement part designs” take two or three iterations to finalize.

The number of design iterations correlates with the complexity of the design ( or: complexity of the design requirements ).

We don’t dive into the “implementation iterations” within a single design version. Implementation Iterations is the process of “tweaking” a design ( small changes ).

One of the opportunities that may be exploited when using the 3D Printing implementation process is that the “replacement part” may be customized for a “perfect fit” with the “other parts”. In our current example the “other parts” include:

  • The pulley spindle: In our case the pulley spindle was “damaged” when the stock part failed and we have the chance to compensate for the damage.
  • The ball bearings we are using: All “standard parts” are created within specific tolerances ⇒ “standard parts” are not identical and we have the opportunity to adapt the design for the “actual standard parts” we are using.
  • The drum drive belt: Our drive belt has “stretched some” over its years of operation and now we may adjust for the longer length by modifying our pulley’s dimensions.

The “first design” may require a dozen ( or two dozen ) implementation iterations: Getting the “fit” just right:

We routinely modify our “implementation iterations” to minimize print time ( and material consumption ) by printing a sub-section of the design

It’s not uncommon for our “implementation iterations” to 3D print in a minute or two when the complete “sub-assembly” requires a half hour to print.

Using a 3D Printer & an “implementation iteration strategy” allows us to greatly accelerate the design process and achieve a “perfect fit” custom replacement part design

Easy for Additive Manufacturing & Impossible for Subtractive Manufacturing

Easy for Additive Manufacturing & Impossible for Subtractive Manufacturing

Design is specific to the planned manufacturing / implementation process.

Lots of folks ( including us ) would prefer the preceding statement to be false.

If you were planning on using traditional subtractive manufacturing techniques ( Lathes, Mills, Saws, Drills, etc..) you could design a cube that contain a spherical void but you could not manufacture the design.

However you could manufacture the Cube with Spherical Void design if you were using an additive manufacturing process ( 3D Printing ).

You might view our example as ‘contrived’ ( “it is” ) but it does highlight the critical concept of how the planned manufacturing process impacts the design.

We could use subtractive manufacturing techniques to create the Cube with Spherical void design if we split the design in half ( two objects to create one “part” ). Then the modified Cube with Spherical void design would need to consider how the two half objects would be joined to form the “part” ⇒ Possibly by adding “bolt holes” and an “O Ring” recess ( depending upon the requirements ).

To Be Clear: We are not claiming that certain design shapes are ultimately impossible to manufacture ⇒ We are stating that the object design must consider the manufacturing process and is impacted by the manufacturing process.

We are hammering on the Design is specific to the manufacturing / implementation process because in practical application the concept is subtle.

Makers of advanced engineering tools ( software ) have developed marketing terminology to highlight this fundamental concept: Design for Manufacturing.

Most Design for Manufacturing tools post process the design to find & identify manufacturing errors. Great engineering tools identify the manufacturing errors as they are created.

Low cost CAD tools do not have Design for Manufacturing analysis capabilities and we don’t elevate Design for Manufacturing analysis to the must have / required category when evaluating acceptable CAD tools.

You will find that we discuss ( verbose mode ) how our knowledge about our 3D Printer impacts our design decisions and how we implement our design.

Learning to how to use a CAD tool to create 3D designs is relatively easy ( There is lots of information available ).

Learning how to think through the manufacturing process while creating your 3D design is much more difficult ( not a lot of published information ).


The winter started rather harshly ( December 2015 ) in the plains of Colorado: Cold snap to -17 F ( -27 C ) ⇒ The water pipe from the well into the house burst and we were without indoor water for 3 weeks ( We had access to water but we had to go out of the house to the spigot: We designed our water pipe with valves so that if we had a catastrophic failure we could turn a few valves and isolate the problem and keep the water flowing ).

Yes… the fact that the water pipe burst demonstrates that we were not really paying attention to the weather. We could have avoided this “major inconvenience” quite easily if we had been “thinking”…. Murphy’s Law applies to all machines including the human computer.

We replaced the broken water pipe using normal plumbing parts and techniques. We didn’t use our 3D printer but it did get us thinking about what “plumbing parts” we should stock and how we could use a 3D printer to make replacement parts in the future.

3D Printing plumbing parts is possible: We have successfully designed “plumbing parts” for our “automated grow-room project” including one way valves, “T”s and manifolds.

However, while our pump system in the automated grow-room project pushes hundreds of gallons of water an hour the pressure is very low ( 2 – 10 PSI) .

The Ranch’s well is 35 PSI…. That increase in pressure as well as the operating environment ( temperature ) requires “testing” before deployment: It is “not fun” to crawl under the house and work on the plumbing ( not a good test environment ).

Our next challenge was a frozen return pipe to the septic system. Fortunately, it only impacted half the house and allowed us to simply wait for warmer weather.

Dirty Clothes Pile

Dirty Clothes Pile

As you might imagine 3 weeks without water causes the dirty clothes to “back-up into a large pile”

The Problem with the Dryer:

Murphy raised his determined head and zapped the clothes dryer: No error codes, no warning lights… just stopped working

Fortunately, the web contains an abundance of information. By performing a search on our dryer’s model number ( MEDE300VW1: Located inside the dryer’s door frame ) we were able to quickly learn:

  • How our dryer works
  • How to disassemble our dryer
  • The common causes of dryer failure
  • How to test parts
  • Where to purchase parts
  • How to re-assemble our dryer

When the world wide web was blossoming ( We pre-date the web ) we had such high hopes for the world: Finally, a universal library!

For many the web degraded into entertainment and social media ghettos. While we applaud everyone exercising their God given right to express their “opinions” ⇒ Opinions don’t necessarily represent “useful information”. Meta data about “opinions” is “useful information” but most folks don’t realize it’s “big brother useful” and a primal violation of their privacy.

For us: the web is close to fulfilling the dream ⇒ Universal knowledge that grows with the human experience. We remember this dream every time we need to “fix something” that we purchased and our web searches return gold.

We don’t always find the information we are looking for: products created by small manufacturers ( or… many Chinese made products ) or artisans. The “Library has room to grow”.

Every video, every parts diagram, every blog requires some interested party to invest their time and create and publish the data on the web. In the most basic terms “someone must spend their time and money” creating content.

In our current example many of the folks publishing the excellent information covering our clothes dryer are corporations selling appliance parts. Makes sense: If you don’t know how to replace the part why would you purchase it?

For our efforts our use of the “appliance parts seller” published information is a tad exploitative: We have no intention of purchasing a replacement part from the seller yet we gobble up their data.

We intend to “balance our karma” by publishing this blog: sharing the knowledge has two purposes:

  • Give others the opportunity to see how to use a 3D Printer to solve everyday challenges ( like fixing a clothes dryer )
  • Make a point to “appliance parts sellers”: There is a disruptive technology ( 3D Printing ) that will eventually evolve the “replacement parts” business model.
    • No, this isn’t a message heralding the end of the “parts seller business model”.
    • The message is quite simple: Knowledge will become more valuable then parts… If you are an “appliance parts seller” you might want to consider investing in the development of printable 3D models that you sell in addition to “replacement parts”…

Maytag 3000 series dryer with the top, front panels and dryer drum removed

After disassembling our clothes dryer our “problem” became very clear: The original tension pulley on the drum belt had experienced a catastrophic failure.

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The dryer had been squealing like a “stuck-pig” for a while. We knew something was wrong but the dryer continued to operate.

Buckaroo was frustrated that KRanch was willing to ignore the high pitched howling and made strong arguments for initiating repairs prior to total failure.

Buckaroo was correct but missed the fact that KRanch was stressing over “available funds”. ( Real life: No perfect answers )

Fortunately, by the time clothes dryer had failed KRanch had developed sufficient skills and experience to design a replacement part.

Part Dimensions

Drum drive belt tension pulley spindle

CB Digital Caliper

Essential Tool: Caliper

We took out our digital caliper and started making measurements of both the original pulley as well as the pulley spindle.

Maytag Dryer Pulley Spindle Dimensions

DescriptionDimension ( mm )
Spindle Diameter12.9
Spindle Length24.4
Spindle Notch ( Keeper ) Diameter10.2
Spindle Notch ( Keeper ) Width2

Maytag Dryer Pulley Dimensions

DescriptionDimension ( mm )
Pulley Diameter42.05
Pulley Outside Diameter46.96
Pulley Width21.16
Pulley Belt Keeper Wall Height2.22

While we were measuring the Pulley Spindle we discovered that it had been damaged: significant groove on the bottom of the spindle. Probably created as the pulley disintegrated ( over time ). We found the groove with our fingers ( touch ) without removing the belt tension arm for inspection. We were confronted with three choices:

  • Replace the complete belt tension arm ( including spindle )
  • Repair the pulley spindle ( probably with a file to remove any “high spots” )
  • Design a pulley spindle cover ( adapter )

The pulley spindle is a ½” ( 12.7 mm ) rod. Normally, we would start our design process planning to use either a ½” bearing or bushing.

Due to our experience with the dryer “screaming at us” the thought of using a bushing was flushed early during design architecture exploration.

Not all bushings “scream” when they fail: Nylon, self lubricating bronze, etc..

Steel bushing are typically strong, inexpensive & long wearing => And they will “scream loudly” ( if not lubricated routinely or fail )

Not all bearings are “maintenance free”: we only purchase sealed, no maintenance bearings.

6203 2RS 5/8" Bearing

6203 2RS 5/8″ Bearing

Reviewing our “standard parts inventory” of bearings we realized: We didn’t have any ½” bearings ( We do stock ½” bearings but they are very popular in our project designs ⇒ all gone… ). We did have an ample collection of 5/8″ bearings.

Combing the fact that the pulley spindle had been damaged and our lack of ½” bearings the decision to implement our design with 5/8″ bearings and a spindle adapter ( change the spindle diameter from ½” to 5/8″ ) was “easy”.

We also liked the fact that the 5/8″ bearings we have are relatively inexpensive ( $2.37 each ) and supports loads greatly in excess of our application:

  • Static Load: 4.75 kN ( 1068 pounds-force )
  • Dynamic Load: 9.95 kN ( 2237 pounds-force )

Using “what you have” is an easy decision. However, it does add design requirements:

  • We needed to explicitly prevent our “spindle adapter” from becoming a “bushing” ( We didn’t think a PLA bushing would last very long in the dryer. )
  • We had to insure that the 5/8″ bearings would “fit”: Not “too large”

The Dimensions of the 6203-2RS 5/8″ bearing are contained within the diagram:

6203-2RS 5/8" Bearing Dimensions

6203-2RS 5/8″ Bearing Dimensions

Design 1:

The first design iteration was focused on “getting the fit nailed”:

  • To the Pulley Spindle
  • To the bearings
  • To the drum belt

A portion of creating a “good design” is knowing a variety of techniques for “post processing” the 3D Printed parts ( skills / experience / tools / inventory ) and knowing how the 3D Printing process and printer operate.

Is your 3D Printer tuned?

How closely do calibration object’s dimensions match design model’s specifications?

Our 3D Printer is tuned and profiled.

Cylinder Seam

If you use a Fused Filament 3D Printer and print a cylinder there will be a seam in the cylinder. You might be able to distribute the seam around the circumference of the cylinder within the slicing tool but the seam exists and alters the object’s final dimensions.

It’s possible to increase the diameter of the design ( interior of cylinder ) to offset for the seam or you might prefer to file ( remove ) the seam as a post production operation. A “perfect cylinder” will have a greater surface area contact with “mated parts” then a cylinder with a seam.

You might also consider decreasing the diameter ( exterior of cylinder ) and adding another material ( tape ) as a post processing operation and eliminate the seam with careful application.

3D Printers are driven by a “digital process” that introduces dimensional errors. The most often overlooked aspect of the “digital design process” is the 3D model’s resolution. When creating round objects ( like cylinders ) low resolution 3D models create “larger” dimensional errors then high resolution models during “slicing”.

Digital Approximation Of A Circle

Digital Approximation Of A Circle

Round objects are segmented into a collection of straight lines ( actually triangles ) during 3D Printer model generation.

3D Slicing engines consume specific formats of 3D models. These “slicing input formats” are all some derivative of surface triangle mesh models

Within a “slice” ( single plane of the object ) “triangles” devolve into “straight lines”. A 3D Model with small triangles ( small line segments ) is “high resolution” and provides a more accurate ( dimensions ) representation of the object.

The point of these observations is:

  • A design may be ( usually is ) created using 3D Printed objects in conjunction with other materials and processes
  • The 3D printed design must consider the complete “fabrication process” and not just “object dimensions”
  • The 3D printed design must consider the operation flexibility of the slicing engine.
  • Design model resolution ( as fed into the slicing engine ) is critical
  • If your 3D printer is not tuned then “precision” is impossible.

The design requirements generally impact the “best approach” to use in the design construction.We have noticed that the deviation introduced by the “seam” is related the cylinder wall’s thickness:

  • Thin wall cylinders ( one of two layers ): The seam deviation is large and distribution around the circumference of the cylinder is not possible.
  • Thick wall cylinders ( greater then 2X the slicer perimeter setting ): The seam deviation is small and distribution around the circumference of the cylinder is possible )

In classic engineering terms we would express the seam deviation as a percentage of the cylinders diameter and the deviation would be larger for small diameters cylinders and smaller for large diameter cylinders.

Seam Deviation = ( Seam offset distance / Cylinder Diameter ) * 100%

3D printing does not alter the classic engineering definition but it also does not completely describe the “behavior” of a fused filament 3D Printer.

Note: The seam challenge is specific to extrusion based 3D Printer technologies. If you are using a powder bed with inkjet head 3D Printer there is not a seam to create a challenge.

Powder Bed with Inkjet Head 3D Printers have other challenges but the “cylinder seam” is not one of them.

Yes, we are once again hammering on the fact that the manufacturing process impacts the design process.

For a variety of reasons we decided to create our design using three 3D printed objects:

  • Spindle adapter: ½” to 5/8″
  • Inside ( closest to the tension arm ) Pulley cover.
  • Outside Pulley cover.

When designing any part the assembly process must be contemplated. We could have printed the pulley body as one piece but then we would not have been able to insert the 5/8″ bearings.

Spindle Adapter Requirements:

  • High Friction “press fit” onto the pulley spindle
  • High Friction “press fit” to the interior of the 5/8″ bearing
  • Provide outside bearing keeper ( don’t let the pulley wander off of the spindle ) without interfering with pulley bearing movement

The first thing to notice is that an adapter from ½” to 5/8″ has a cylinder wall thickness of 1/16″ => 0.0625″ ( 1.5875 mm ). With a 0.4 mm extruder nozzle the wall thickness is approximately 4 extruded strands wide.

After determining:

  • To “file the seam” on the interior of the spindle adapter to achieve a high friction fit with the original metal spindle
  • To use 1 mils ( 0.0254 mm ) thick copper tape on the exterior of the spindle adapter to create a high friction fit with the interior bores of the 5/8″ bearings

After creating test prints and “tweaking” the design dimensions we created our final dimensions for the spindle adapter:

Final Dimensions: Pulley Spindle Adapter

Final Dimensions: Pulley Spindle Adapter

The final wall thickness of the spindle adapter’s cylinder is 0.93 mm ( a little more than 2 extruded strands wide ).

We decided to use the copper tape on the exterior of the spindle adapter to:

  • Eliminate the seam
  • Provide a harder wear surface for the bearings
  • Allow us to alter the exterior diameter for each ball bearing ( custom fit ). Ball Bearings have manufacturing “tolerances”: For the Bearings we are using the the interior bore tolerance is +/- 0.10 mm ( Not very good but they are inexpensive ).

Our Next step was to create test prints to achieve the correct length for the barrel of the spindle adapter. Each bearing is 12 mm wide ( +/- 0.10 mm ) and we found that a length of 24.15 mm was needed for the specific bearings we were using:

Pulley Spindle Adapter Length

Pulley Spindle Adapter Length

The final design task for the pulley spindle adapter was the creation of a “keeper” that would prevent the pulley bearings from “wandering” off of the open end of the spindle.

Pulley Spindle Keeper Requirement

Pulley Spindle Keeper Requirement

For our V1 design we planned on using the original “pulley keeper” to secure our pulley adapter on the spindle.

Original Spindle Pulley Keeper ( Tri-Ring )

Original Spindle Pulley Keeper ( Tri-Ring )

On the side of the pulley closest to the tension arm there is a nylon spacer washer:

Pulley Spacer Washer

Pulley Spacer Washer

Given the length of the spindle adapter required to fit our dual 5/8″ ball bearings combined with the thickness of the pulley spacer washer and the total distance available on the original pulley spindle before the keeper ( Tri-Ring ) we were left with 0.45 mm to implement our Spindle Adapter Keeper. We decided to implement a spindle adapter keeper with a thickness of 0.35 mm mainly due to the fact that our first layer ( 3D Printing ) is 0.35 mm and our normal layer height ( 3D Printing ) is 0.25 mm ( which makes 0.45 mm thickness a difficult dimension to achieve without re-tuning our 3D printer for layer heights of 0.10 mm => Not that difficult of a task but it would also more than double our object print time. )

Pulley Spindle Adapter with Keeper

Pulley Spindle Adapter with Keeper

We were concerned that a keeper thickness equal to one 3D Printing layer height would not provide sufficient structural strength to keep the pulley from wandering off of the spindle adapter.

One one hand: Our 3D Printer is tightly tuned and we achieve excellent extruded strand to extruded strand bonding withing a single layer:

Single Layer Keeper

Single Layer Keeper

On the other hand: The Spindle Adapter Keeper is only one layer thick and is “flexible”.

Since we have “no idea” what the lateral force vector on the pulley is => Maybe this will “work”?

Spindle Lateral Forces

Spindle Lateral Forces

Ideally, the lateral force directed along the spindle shaft would be zero. In all real machines there will be a lateral force created by a cost compromise decision that will impact the rigidity of both the pulley tension arm and the spindle ( Thick metal parts versus thin metal parts ). Almost always: The lateral force will be directed toward the open end of the spindle. As the machine ages ( is used ) the lateral force tends to increase => As parts slowly yield to the operational forces.

We rationalized our “design compromise” by telling ourselves that the “Spindle Adapter Keeper” would be further strengthened by the original spindle keeper Tri-ring.

The original tri-ring keeper had been destroyed when the original pulley failed. When we designed our replacement tri-ring we increased the width to support our “rationalization”.

Original Spindle Keeper ( Tri-Ring ): Modified Design

Original Spindle Keeper ( Tri-Ring ): Modified Design

V1 Pulley Spindle Adapter with Copper Foil Tape

V1 Pulley Spindle Adapter with Copper Foil Tape

Spindle Keeper ( Tri-Ring ): Modified

Spindle Keeper ( Tri-Ring ): Modified

We filed the interior of the spindle adapter and applied a few layers of copper foil tape to the exteriour shaft ( untile we had a ‘perfect fit’ with the interior bores of the bearings.

V1 Spindle Adapter mounted in 5/8" bearings

V1 Spindle Adapter mounted in 5/8″ bearings

Inside Bearing Cover Requirements:

Interior Cover

Interior Cover

The Inside Cover is closet to the tension arm and:

  • Must not rub against the tension arm
  • Provide a high friction “press fit” to the outer diameter of the 5/8″ Bearing
  • Provide a “retaining ring” to keep the bearing confined within the pulley.
  • Provide a “retaining wall” for the drum belt ( Keep the belt from wandering off of the pulley
  • Mate with the Outside Cover: Concentric end to end mate ( no overlap )

The first requirement: “must not rub on the tension arm” limits the thickness of the “retaining ring” containing the bearing. The thickness of the retaining ring must be less than the thickness of the spindle spacer washer.

The final requirement: “Mate with the Outside Cover” is an architectural decision: For our first design attempt we decided that we would create a cover for each of the two bearing we are using and then use “tape” around the outside diameter of the pulley to hold the two covers together. The use of “tape” to join the parts was not our only option but since we had no idea of the magnitude of lateral forces the pulley would be exposed to it was viewed as a reasonable first design iteration.

When creating 3D models for use with a 3D Printer it is “good practice” to think about “How” the object will be printed. You are able to save time in the “slicing engine” if you don’t have to rotate your part prior to slicing. For our tools and slicing engine the “X-Y” plain aligns with the “3D printer platter ( printer substrate )”

For the Inside cover we decided the 3D Printer “order” should be:

  1. Bearing Retaining Ring Start & Belt Retaining Wall Start should be the first layer
  2. Bearing Retaining Ring Stop & Cover Cylinder Start
  3. Belt Retaining Wall Stop
  4. Cover Cylinder Stop

We try to avoid support structures in our 3D Printing ( They use additional material, increase print time & increase post printing processing => removing the support structures ). Support structures are required for “overhanging structures” => avoid creating overhanging structures

Inside Cover Design: Avoiding Support Structures

Inside Cover Design: Avoiding Support Structures

Yes, this is a trivial example and should be “obvious” to novice 3D Printer users… but it might not be “obvious” to the novice 3D model developer so we thought it might be useful for some folks.

When creating complex structures avoiding overhangs is not obvious and spending a little time up-front “thinking it through” will save hours of work ( and avoid frustration ).

Once the “print direction of the model” has been determined the order for creating model features may or may not mirror the print order. The “key concept” is to “think through” the fabrication process before beginning the feature creation process.

The Inside Cover feature creation order was:

  1. Create a “base” that will have a height equal to the thickness of the bearing retaining ring
  2. Create the cover cylinder
  3. Create / Complete the belt retaining wall feature

We began our design with a “base feature” that is a cylinder with:

  • Interiour Diameter established to provide a Bearing retaining ring: 36 mm
  • Exteriour Diameter established to provide a Belt retaining wall: 50 mm
  • Thickness equal to the Bearing retaining ring thickness: 0.5 mm
Inside Cover Design: Retaining Ring Feature

Inside Cover Design: Retaining Ring Feature

It’s time to talk about “Design Tools”. If you design “functional things” then you will want a parametric mechanical CAD design tool. “Parametric” implies that you specify “dimensions”: You set the size.

If you design more than a “few things” you will want a parametric mechanical CAD design tool that has the ability to support “variables” and equations. Your design tool must provide some method to “share” variables between different object designs ( Import / Export is common and “good enough” => Tools that elevate varaibles and equations to “constraints” are ‘awesome’. Why?

Do you want to re-enter the dimensions for common objects ( Like Bearings & Bolts & …) more than once

We use variables and equations to create our design dimensions routinely. For any “standard object” we create dimension variables

Inside Cover Design: 5/8" Bearing Variables

Inside Cover Design: 5/8″ Bearing Variables

There are many more “required features” for a good 3D model design tool.

If your 3D modeling tool does not support variables and equations then maybe you should start looking for a new 3D modeling tool.

Our next feature was the cover cylinder ( the belt pulley contact surface ):

Inside Cover Design: Pulley Belt Surface

Inside Cover Design: Pulley Belt Surface

When you are creating your design you should also consider: How you will modify the design to achieve “perfect fit”?

For any surface that is mated to a “standard part” we add a tweaking “equation” to the standard parts dimension:

Surface Dimension = Standard Part Dimension + “tweaking equation”


Tweaking Equation = ( Tweaking Term * Printer Nozzle Diameter )

Our Tweaking Equation probably generates a number of questions that start with:

  • Why are we using “Printer Nozzle Diameter” in our tweaking equation?

First, feel free to develop and use your own “tweaking equation”. We are not convinced that we have the “perfect” tweaking equation.

Our “tweaking equation” development thought process:

  • The Width of material deposited is ( roughly ) equivalent to the diameter of the printer nozzle
  • The width of deposited material establishes the “positive” object space resolution
    • The 3D Printer’s mechanical X-Y resolution establishes the “negative” object space resolution

In theory we are adding or removing ( negative tweaking term value ) “one layer” of deposited material at a time from the object until we have achieved “perfect fit”.

In practice we routinely use fractional “tweaking term” values: 0.25, 0.5, 0.75. Fractional tweaks “work” because our 3D Printer’s X-Y resolution ( 0.01 mm ) is much higher than “extruded material width” value ( “off the shelf”: 0.4 mm ) and “most of the time” there is ample “negative space” available in the design.( Negative space hides within solid object structures => as long as width of the solid object exceeds two times the slicer setting for the number of “perimeters”. )

5/16" Bolt NUT Knob: Negative Space

5/16″ Bolt NUT Knob: Negative Space

We have found that our “tweaking equation” provides a good conceptual model but it does not scale with:

  • Nozzle Diameter
  • Material Types: PLA vs. ABS vs. Nylon vs. Graphene PLA vs. etc…
  • 3D Slicing Setting: Filament Settings ( that impact flow rate )
  • 3D Printer Tuning

By “does not scale” we are implying that we must alter the “tweaking term” to achieve a perfect fit.

Our “tweaking equation” is “incomplete” ( as opposed to “wrong” ). The Design of a custom object is “impacted” ( limited ) by the capabilities of the fabrication method and the materials used.

To be absolutely clear: A design model will need to be “re-tweaked” for a number of reasons after achieving a “perfect fit”:

  • Change the printing material
  • Use a different type of 3D Printer
  • Change the Extruder Nozzle
  • Re-tune the 3D Printer ( usually after extruder failure & repair or replacement )
  • Change Slicing engine settings that impact “filament flow rate”

Inside Cover Design: Pulley Belt Surface Dimensions

Inside Cover Design: Pulley Belt Surface Dimensions

The Inside & Outside Bearing Covers both have a thin ( 0.8 mm ) “Belt Surface”. The decision to use a thin cylinder of the belt surface was based on our measurements of the original belt pulley ( 42.05 mm ) => Keeping in mind that the original suffered significant deformation as it failed.

While it is relatively easy to find parts diagrams for appliances on the web it is exceptionally difficult to find “dimensions” for a specific appliance repair part on the web.

The “thin wall” was not a concern because:

  • The “thin wall” is completely supported by the 5/8″ bearing
  • The “thin wall” is completely solid => No internal “negaitve spaces” to collapse & cause failure
  • We had decided to apply copper foil tape to both join the Outer and Inner Pulley Covers together and provide a long wear surface for the belt to ride over.

If you are paying close attention you will notice that the “belt surface” cylinder is not split evenly between the Inside & Outside Covers => The Inside cover has a taller cylinder ( 13 mm ) then the Outside Cover ( 10 mm ). The Inside Cover “overlaps” the edge of the 5/8″ bearing contained within the Outside Cover ( A little trick to help assure alignment ).

Inside Cover Design: Thicken Belt Retaining Wall

Inside Cover Design: Thicken Belt Retaining Wall

The final feature of the Inside Cover “thickens” the belt pulley retaining wall:
Inside Cover: Thicken Belt Retaining Wall Design Sketch

Inside Cover: Thicken Belt Retaining Wall Design Sketch

Another set of “must have” 3D Design tool capabilities: Geometric Constraints

  • Vertical
  • Horizontal
  • Collinear
  • Parallel
  • Coincident
  • Perpendicular
  • Mid-Point
  • Equal
  • Symmetric
  • Intersection
  • Coradial
  • Concentric
  • Tangent
  • Locked
In our example the interior edge of our “riser cylinder” is co-radial with the outside edge of the Pulley Belt Surface cylinder and the exterior edge of the “riser cylinder” is co-radial with the outside edge of the base cylinder.

Using geometric constraints simplifies “design modifications”: Make the “tweak” in one location and it propagates throughout the design.

In our current design we are constraining new feature sketch figures to existing object features. It also possible to constrain sketch figures to each other ( in a good 3D modeling tool ).

Inside Cover: Completed Design

Inside Cover: Completed Design

There is one final detail that is worth pointing out: The Belt Retention Wall extends over the top of the ball bearing.

Inside Cover: Completed Design - Cross Section View

Inside Cover: Completed Design – Cross Section View

The Belt Retaining Wall’s overlap of the 5/8″ Bearings outer surface is necessary in order to prevent the pulley from “rubbing against” the tension arm.

Another feature requirement for a “good” 3D Modeling tool: Ability to create cross-section views.

It is debatable if “cross-section views” are required for a “basic” 3D modeling tool.

Based on our cumulative design experiences we have noticed instance where “object feature creation” would have been difficult if we didn’t have “cross section view” capability but not impossible.

We mainly use cross section views to “think through” our implementations as we compare the final design to object requirements ( normal design review ). Design Cross Section Views are extremely useful.

Outside Cover Requirements:

Version 1 Bearing Outside Cover

Version 1 Bearing Outside Cover

The Outside cover is at the “open end” of the spindle.

  • Provide a high friction “press fit” to the outer diameter of the 5/8″ Bearing
  • Provide a “retaining wall” for the drum belt ( Keep the belt from wandering off of the pulley )
  • Mate with the Inside Cover: Concentric end to end mate ( no overlap )

The Outside Bearing Cover has a subset of the requirements used for Inside Bearing Cover. The missing requirement:

  • Must not rub against the tension arm
It is as critical to not over define an objects requirements as it is to make sure your object requirements are complete.

Each object of a part has a unique set of requirements. If this statement is not true then you should ask yourself if the the object is necessary.

In our current “dryer belt pulley” design project we use the freedom created by the missing requirement to strengthen ( thicken ) both:

  • Bearing Retaining Ring
  • Belt Retaining Wall

This isn’t a trivial “adjustment”: We know ( based on our experience ) that any lateral forces acting upon the pulley will be directed toward the open end of the pulley spindle.

The Outside Bearing Cover has two dimensional difference from the Inside Bearing Cover:

  • The Belt Surface Cylinder has a shorter height
  • The Belt & Bearing Retaining Wall / Ring thickness is increased

We made the decision to place the Belt Retaining Wall in parallel with the Bearing Retaining Ring ( No Overlap of the Belt retaining wall with the Bearing’s Outside surface that is in contact with the interior of the Belt Surface Cylinder ).

Version 1 Outside Cover: Completed Design with Cross Section View

Version 1 Outside Cover: Completed Design with Cross Section View

There are a number of methods 3D Model development tools provide to help a designer create “slightly altered” designs:

  • Save As: Create a new distinct 3D model file
  • Configurations: Create a “derived object” within the same 3D model file

Save As

  • Advantage: Universally available
  • Disadvantage: Design changes common to both designs must be made in more than one file

Configurations is a “data set management” technique ( collections of “sketches” & collections of “dimensions” ) that allows the user to quickly create “derived objects” which should allow the user to designate which “dimensions” should be shared and which design “dimensions” are specific / locked to each configuration.

In practice configurations are an “advanced feature” => Challenging to learn. We have found that we are able to use configurations effectively after many hours of “trial and error” attempting to “achieve our goal”.

The “tool could do it” but we had to change our object features to separate “shared” dimensions from “configuration specific” dimensions => The Designer must change “how” they think about creating objects.

Once the Designer learns how to use configurations effectively productivity is increased for complex parts

It’s debatable if configurations increase productivity for simple parts where managing “differences” is simple ( low number of differences and / or a low number of dimensions )

For this simple design project we used “Save As” and created a distinct 3D model file.

Since we have the ability to use variables and equations for “dimensions” and we have the ability to “export and import” dimensions we have the ability to align shared dimensions between the design files.

The import / export dimensions “work around” becomes painful when you have a complex object that has “lots of dimensions”. When you have “lots of dimensions” it would be extremely useful to have “data management tools” to help!

From a 3D model tool feature perspective:

  • Required: “Save As”
  • Nice to Have: “Configurations”

Nice to Have evolves to Required when complex object design is “routine”.

You might be thinking: Wait! The Inside Cover has a pulley belt surface of 13 mm and the Outside Cover has a pulley belt surface of 10 mm for a total belt pulley surface of 23 mm and yet each 5/8″ ball bearing has a width of 12 mm creating a minimum width of 24 mm for two bearings “side by side”

If that’s what you were thinking: Very Good!… You have what it takes for solid “design reiew”.

We intentionally left a gap between the Inside Cover and the Outside Cover belt pulley surfaces:

  • At the top on any thin wall cylinder you will discover that the 3D Printer deposits a “bump” as it “stops” and then moves away from the object being printed: Instead of filing away the bump we planned to use it to “lock the rotation” of the two cover halves
  • By leaving a little space we are able to “compress” the two 5/8″ bearing inside of the covers during the assembly process leaving absolutely “no space” between the two bearings

Introduction to the filament Extruder

What creates the bump at the top of the cylinder? Momentum

Although the extruder drive motor is capable of stopping quickly the molten material in the extruder is a fluid in motion => Takes a little longer to stop.

There are methods to minimize the effects of momentum:

  • Slow the printing process as the end of the print nears
  • Apply negative pressure to the molten material at the end of the print => Retract Filament

To understand how you could eliminate the bump from the top of the cylinder wall without post-processing the object ( filing / cutting ) it is time to dive into how the filament extruder works.

Filament Extruder Parts: Conceptual

Filament Extruder Parts: Conceptual

A fused filament 3D Printer’s extruder is an interesting “machine”. A Motor feeds a solid filament into the heater block where the filament does two things:

  • The solid filament acts as a “piston” applying pressure to the “molten filament” to force it out of the extruder’s nozzle.
  • The solid filament “melts” to become part of the “molten reservoir” inside the heater block chamber.

In order for the filament to act as a “piston” on the molten pool the filament must be solid. The extruder’s cooling tower is essential for quickly dissipating the heat from the heater block allowing the filament to remain solid until it enters the “molten reservoir zone”. Good cooling towers are made from metal ( great thermal conductor ) & Great cooling towers have a fan mounted to the cooling tower ( fast removal of heat ).

The volume of the heater block’s reservoir has a significant impact of “maximum printing speed” that you will encounter if you start using “large diameter nozzles” ( above 0.8 mm diameter ).

Filament Extruder: Running Too Fast

Filament Extruder: Running Too Fast

Theoretically, a larger diameter nozzle will print an object faster than a smaller diameter nozzle because it is depositing more material in a single pass. And while larger diameter nozzle’s generally do print faster there is a limit to how fast your are able to print constrained by the reservoir volume. If you exceed the reservoir volume you will be attempting to drive “solid filament” through the nozzle and the print will fail ( The extruder motor will either stall or start gouging bits of filament from the filament currently in the hob { filament drive gear } ).

The “solution” is to replace the heater block with a larger volume reservoir heater block when using large diameter extruder nozzles.

We believe having a modular extruder is a must have requirement for a fused filament 3D Printer. Having the ability to swap out the standard heater block for one that has a larger molten reservoir is one aspect of “modular design” that is often overlooked. If you are new to fused filament 3D Printers you might be tempted to think that having a collection of extruder nozzle diameters to choose from is sufficient => And you would be correct as long as you are willing to limit your maximum print speeds.

Some folks will be tempted to increase the “rate of heating” of the filament using a standard heater block by increasing the filament temperature setting for the heater block ( a slicing tool setting ).

This is a mistake ( That we have experience with => Been there, done that ): There are times during a print when your printer is running “full speed” and there are times when your printer is running “much slower”. Increasing the heater block’s temperature might solve the “molten material availability” problem when operating at “full speed” but will also change the viscosity of the molten material ( or worse, burn the molten material ) creating lots of 3D Printing defects ( that we call “creating spiderwebs” or “stringies” ) and will definitely alter the “precision” of your 3D Printer.

A 3D Printer is “tuned” when it creates objects that have the same dimensions ( within tolerances you define ) as the dimensions defined in the 3D model. A critical aspect of “tuning” is dialing in the “flow rate” of the extruder material from the nozzle. Molten Filament “flow rate” is an artifact of:

  • Filament material type: PLA Vs. ABS Vs. Nylon Vs. etc…
  • Extruder motor filament feed speed
  • Heater block temperature setting
  • Heater block molten reservoir volume
  • Extruder nozzle diameter

Keeping in mind that temperature characteristics of any “filament” will vary from reel to reel ( same “type”, same “color”, same “manufacturer” ) due to variances in the manufacturing process. Filament “variances” are minimized when the filament is from the “lot” => You might considering purchasing larger volumes of filament in a single purchase order and “hope” that all of the filament reels are from the same “lot”.

Filament temperature characteristics definitely are impacted by colorants added to the filament during the manufacturing process. When first tuning a 3D Printer we always use Natural ( no color pigments ) filament to establish our base line.

You should also consider that setting the “heater block’s temperature” is impacted by a number of variables including the precision of the temperature sensor used in the temperature range you are operating within. All temperature sensors are “lagging sensors” ( they require time to respond ). No two temperature sensors are identical ( although they may have exactly the same part number ). If your temperature sensor tells you that your heater block is running at 195 C you don’t really know the temperature of the heater block unless you “calibrate” your tempeature sensor.

PID Block Diagram

PID Block Diagram

PID Control Graph

PID Control Graph

A good 3D Printer controller will use a Proportional–Integral–Derivative ( PID ) algorithm to stabilize the temperature within the heater block. The PID algorithm must be “tuned” for each extruder setup ( Includes changing filament types => You will be changing the extruder’s operating temperature ).

In engineering terms the PID algorithm is a third order equation that compensates for the current, past & future errors in temperature from a “desired temperature”.

In practical terms the implication is that your heater block is constantly “passing through” the “desired temperature” as it reaches higher temperatures and turns off the flow of electricity to the heater element and then begins to decrease in temperature and then falls below the “desired temperature” and then turns on the flow of electricity to the heater element.

If you clicked on the reference links we provided in the two preceding paragraphs you should question our assertion that the temperature oscillates around the “desired temperature” as the entire reason for implementing a PID temperature control algorithm is to create a “damped response” ( non-oscillating ). The PID controller does create a “damped response” for the 3D Printers extruder at “steady state” ( fixed set of “disturbance” values ). The unfortunate reality is that 3D Printers are real-world machines that operate in a continuously varying environment. Some times the filament is fed “faster” and sometimes “slower”. Sometimes the fan cooling the recently deposited material does not interact with the heater block and other times the air flow is directed over the heater block. 3D Printers do not operate at “steady state”. To fully grasp consider: All 3D Printers perform PID auto-tuning with the filament feed rate set to zero ( no filament movement ).

Don’t allow the details confuse you!

At this point you might be scratching your head thinking: This is much too complicated!

The good news: In practice you will not need to deal with the math => You will tell your 3D Printer controller to auto-tune and then you will follow the empirical path:

  • Print Calibration objects
  • Measure the 3D Printed objects
  • Adjust a couple of variables in the slicing engine & firmware
  • Repeat…

The key points to take away from this discussion is that you need a 3D Printer that:

  • Has the necessary mechanical components to meet your needs => If you think you might need to run a large diameter nozzle you will need an extruder motor that is able to produce sufficient torque at the desired feed rate: Minimum 24V drive motor
  • Has a modular extruder
    • Offers multiple heater block options ( molten reservoir sizes )
    • Offers a good variety of nozzle sizes
  • Implements PID for extruder temperature control ( all RepRap & Derivative 3D Printers )
  • Supports a wide temperature range ( to support a variety of Filament types ) => High Current draw

The extruder requirements are one of the reasons why we selected the MendelMax 3 as our base platform for 3D Printing.


V1 Belt Tension Pulley Parts

V1 Belt Tension Pulley Parts

The assembly is straightforward and there is more than one method. The assembly process we used:

  1. Press both 5/8″ bearings onto the adapter spindle
  2. Press the Outside Pulley Cover onto the 5/8″ bearing closest to the spindle adapter keeper
  3. Press the Inside Pulley Cover onto the remaining 5/8″ bearing
  4. While pressing the Inside and Outside Pulley Covers together apply a layer of copper ( or aluminum ) foil tape to the pulley belt surface

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To install the drum belt tension pulley on your dryer:

  1. Press the pulley assembly onto the original ( metal ) spindle
  2. Press the tri-ring keeper onto the original ( metal ) spindle

The most difficult assembly step ( for us ) was pressing the pulley assembly onto the original ( metal ) spindle due to the high friction fit we designed into the spindle adapter.

We were not caught by surprise: We knew that our spindle adapter had a “tight fit” to the original ( metal ) spindle based on our “fine tuning of the fit” during design implementation testing.

9/16" - 1/2" Drive Deep Well Socket

9/16″ – 1/2″ Drive Deep Well Socket

To seat the pulley on the original ( metal ) spindle we used a 9/16″ ( 1/2″ drive ) deep well socket. You might be able to use a regular ( normal length ) 9/16″ socket but we didn’t want to take the chance that we might damage the socket.

Find the smallest socket that slips easily onto the metal spindle shaft => Avoid damaging the spindle shaft and the spindle adapter.

Sometime you need to make tools

If you don’t have a collection of deep well sockets it’s time to 3D Print a seating tool.

You might want to 3D print a “seating tool” if you have a deep well socket where the drive end is slightly recessed ( normal ). We want to apply pressure to the spindle adapter as close to the spindle as possible ( and not the outer edges of the thin “retaining wall”). It is very easy to damage the spindle adapter during installation.

Yes, we learned this lesson the hard way…. frustrating!

By 3D Printing a spindle adapter seating tool we were able to apply force to the strongest surface of the spindle adapter ( close to the original metal spindle ).

We started our design by using Save As with our spindle adapter design 3D model file.

We modified the core cylinder:

  • We increased the interior diameter of the cylinder so that it would easily slide over the original metal spindle
  • We increased the thickness of the cylinder walls to 5mm
  • We increased the length of the cylinder to 1.5″

Spindle Adapter Seating Tool: Core Cylinder Sketch

Spindle Adapter Seating Tool: Core Cylinder Sketch

By starting with the Spindle Adapter 3D model file we were able to minimize the number of “test print” iterations required to obtain a perfect fit to the original metal spindle. We simply increased the “tweaking term” in our equation for the diameter of the interior of the core cylinder.
Spindle_Adapter Seating Tool: Core Cylinder Length Extrusion

Spindle_Adapter Seating Tool: Core Cylinder Length Extrusion

Why do we create models using metric dimensions?

The slicing engine and the 3D Printer default to metric.

While it is possible to force the tools into English measurement mode we have found that we make far fewer mistakes by sticking with metric dimensions. While our conversion errors were frustrating they did not cost us millions of dollars. Still, we learned our lesson the hard way and once we made the decision to work in metric only we eliminated one source of our design errors.

We “think” in English dimensions => mils, inches, feet, yards, miles. If you ask us how long our driveway is we will tell you 1/2 mile.

Our subtle point: Since the slicing tool and the 3D Printer controller default to metric ( every time ) it is easy to create conversion errors if you create your 3D models using English dimensions.

Our next step was to make the base end of the cylinder solid => Give the hammer a solid surface to “tap”.

Spindle Adapter Seating Tool: Solid End Sketch

Spindle Adapter Seating Tool: Solid End Sketch

We began with the sketch for the spindle adapter’s retaining right and simply converted the the retaining ring’s outer figure ( Circle ) to a reference figure ( comment ) so that we would create a solid end cap.

More about 3D Modeling Tools

Finding The Center Of A Rectangle

Finding The Center Of A Rectangle

The ability to convert figures to and from “reference figures” is a must have requirement for a 3D modeling tool.

Our current example is trivial: We could have simply deleted the retaining ring’s outer circle.

Using geometry is much easier than using dimensions for a variety of frequent tasks: Like finding the center of a rectangle ( another trivial example ).

As designs become more complex the need for reference figures increases. If you have familiarity with old school drafting then you already understand that reference figures are critical.

The End of the World as We Know It

Fortunately, our education predates “common core” and the U.S. Department of Education.

There was a time when the next generation was exposed to real skills: Metal Shop, Wood Shop, Drafting Class, Electronic Design, Cooking, Sewing, Typing in Junior High School ( 7th, 8th & 9th grades ).

These skills often made understanding advanced mathematics ( like geometry ) much easier. Why? The practical application of mathematical concepts allowed the student to translate ideas from the brain to the hands. Immediately answering that gnawing question of “Why would I ever need to know this?”

We should lament the sorry state of our educational system but we must never translate that sentiment onto the young folks who are taught that how they feel about math is more important then mastering mathematics and the practical application of those concepts into the real world.

We “old geezers” need to pick up the slack of an educational system that appears to be designed to dumb down our future generations by providing mentoring opportunities. The corollary to the “old geezer” responsibilities is that these kids need to realize that they don’t know everything and to approach us old timers with an open mind so that they may soak up practical skills.

3D Printing and the creation of 3D Models makes information that was once old new again.

We made our “solid top” 5 mm thick.

Spindle Adapter Seating Tool: Solid End Thickness

Spindle Adapter Seating Tool: Solid End Thickness

Out last step was to chamfer the open of the cylinder so that all force would be directed onto the spindle adapter very close to the original metal spindle.

Spindle Adapter Seating Tool: Chamfer Open End

Spindle Adapter Seating Tool: Chamfer Open End

The chamfer edge operation is critical as it applies the force of the seating tool to the strongest portion of the spindle adapter near the original metal spindle.

In our example we are using a non-symmetric chamfer edge operation to create a strong tool.

More 3D Modeling Design Tool Requirements

Edge Round Over / Fillet

Edge Round Over / Fillet

Edge Chamfer

Edge Chamfer

If you are familiar with wood working or metal working the concept of “rounding over” and “chamfering” edges should be common knowledge.

Yet, the word “chamfer” is constantly flagged by our spell checker…. So, maybe this is “secret knowledge”

Chamfered Edges are also known as Beveled Edges

Round Over operations are sometimes known as fillet operations. However, we have seen fillet used to reference interior edge operations only. In fact, we have see fillet used to reference both Round Over and Chamfer interior edge operations.

The ambiguity of the use of the word fillet may be representative of the domain of operation: In the domain of metal welding fillet is precisely defined.

Again, don’t allow the definition of terms overwhelm you!

The ability to create fillets and chamfers is a must have requirement for effective 3D modeling of mechanical objects.

If your 3D Modeling tool does not support edge operations => Get a new tool!!

Since we are creating a tool that we are going to tap with a hammer we must think through the implementation => 3D Slicing settings or we will end up with a tool that will fracture in use.

3D Slicing Settings: The “art” of “strength”

We could tell the 3D Model slicing tool to make our seating tool 100% solid: And use lots of filament and wait a long time for the object to be printed.

Actually, this is relatively small and trivial 3D model where changing the settings to create a solid object has very little downside…. We are in the habit of thinking about how we want our 3D Models to be printed and it requires very little time to tweak the slicing engine settings to achieve a good balance of strength, filament usage & 3D Printer times.

It’s our experience that solid objects ( 100 % fill ) don’t print with tight dimensional tolerances => This has to do with heat retention inside the object ( in our opinion )

Fortunately, we have been running tests and reading published research articles for years evaluating the structural strength of different 3D model slicing settings.

Spindle Adapter Seating Tool Slicer Settings: Strong Body

Spindle Adapter Seating Tool Slicer Settings: Strong Body

Spindle Adapter Seating Tool Slicer Settings: Perimeters And Layers

Spindle Adapter Seating Tool Slicer Settings: Perimeters And Layers

Based on our knowledge ( experience based ) we know that we want the vertical walls of the pulley spindle adapter seating tool to be relatively thick so that the force of the hammer is translated into pushing the pulley spindle adapter onto the original metal spindle.

We accomplish this objective by telling our 3D Model slicing tool to create perimeters ( a.k.a. “walls” ) using four parallel deposits of filament.

We chose an interior fill rate of 35% => We have built load bearing parts with a 35% fill rate years ago that are still in operation.

Spindle_Adapter Seating Tool Slicer Settings: Infill

Spindle_Adapter Seating Tool Slicer Settings: Infill

If you remember we implemented an asymmetric chamfer / bevel on the top of our seating tool that started 1 mm below the top. The use of 1 mm was not arbitrary => We were thinking ahead to the implementation. Knowing that we were going to print the seating tool using 0.25 mm “layers” we knew that we wanted the chamfer / bevel to be an integer multiple of the layer height:

  • One Layer => 0.25 mm
  • Two Layers => 0.50 mm
  • Three Layers => 0.75 mm
  • Four Layers => 1.00 mm
  • Five Layers => 1.25 mm
  • etc…

Spindle Adapter Seating Tool Slicer Settings: Strong Top

Spindle Adapter Seating Tool Slicer Settings: Strong Top

By tweaking a few slicing variables / settings we are tuning our object’s implementation for the intended use.

We also set the bottom solid layers to “4” as that is where the hammer will be striking the seating tool and we wanted to provide a crush resistant surface.

Slicing is incredibly flexible

When you are using traditional methods for object creation you never think about the “interior of the object”. At first 3D model slicing might look like a complication for 3D Printing ( or any additive manufacturing process ). However, once you understand the basic concepts you are able to leverage the functionality to create incredible objects.

Disney uses variable density ( fill ) to transform their characters into spinning tops

Using variable density gives the designer the freedom to trade-off structural support ( strength ), flexibility, material usage and 3D print time.

While variable density is an advanced topic sometimes it’s useful to have insight when working through the basics so that the mind may begin contemplating innovative objects. We routinely leverage variable density to increase support for load bearing surfaces while minimizing 3D Print time and filament usage.


After the dryer drum belt tension pulley was installed we re-assembled the dryer:

  • No load ( no clothes in the dryer ) testing => It works!
    • Quiet operation ( nice change )
  • We began processing our now giant pile of dirty clothes

It wasn’t too long before we noticed a problem: When we loaded the dryer with a full ( super sized ) load of blue jeans and towels the dryer drum would not rotate. We knew what the problem was => the drum belt had stretched through years of use ( and a fair amount of misuse as the pulley failed ).

We followed our normal path: We adjusted the load in the dryer until the dryer drum would rotate

About one week later, after processing most of our dirty clothes we heard a resounding “thunk – thunk” and upon inspection we found ourselves in our original position: the dryer was broken!

We eagerly disassembled the dryer

When the clothes dryer first broke we were frustrated having just repaired the water supply to the house.

When the clothes dryer broke after our 3D Printed part repair we were smiling => How did our part fail?

Knowing how to disassemble and re-assemble the appliance eliminates a lot of angst in the repair process. By the time we hit round two of the design process we were very comfortable working on our clothes dryer.


V1 Spindle Adapter Failure

V1 Spindle Adapter Failure

When we removed the dryer drum we found the pulley in multiple pieces within the dryer. The Pulley covers were split apart and located in opposite corners of the interior.
V1 Pulley Covers Split Apart

V1 Pulley Covers Split Apart

Learning the cleaning lesson again

In our first repair effort we did a poor job cleaning the interior of the clothes dryer chassis….and now we were going to pay for that error.

We never found the replacement tri-ring keeper for the pulley.

We assume it splintered into multiple pieces in an explosive failure.

Lesson learned again: Cleaning is part of any repair…

We began our examination of the failure: The first thing we noticed was that the spindle adapter bearing retaining ring was completely removed from the spindle adapter.

For this to happen the tri-ring keeper on the metal spindle had to fail.

V1 Spindle Adapter Failure

V1 Spindle Adapter Failure

The spindle adapter cylinder was still on the metal spindle and the copper foil on it’s outer surface was pristine ( no signs of wear).

To remove the V1 spindle adapter we had to pry it off using a flat blade screwdriver.

Early in the design of the V1 replacement pulley we guessed that our “enemy” would be the lateral force applied by the drum belt => We were correct… and now we had a much better idea of the magnitude of the lateral force ( big )

The fact that we heard two “thunks” as our V1 repair failed and the fact that we found the pulley covers in opposite corners of the chassis suggested that the pulley left the spindle adapter with energy ( velocity ).

V1 Pulley Failure

V1 Pulley Failure

The Good, the Bad & the Ugly

It’s important to examine part failures using as many senses as possible:

  • Sight
  • Sound
  • Touch

It is also imperative for the part to be viewed from multiple perspectives:

  • What Failed
  • What Worked

Leading up to the thought experiment ( imagination ) describing How and Why the part failed. If you are unable to describe what happened you can’t design a remedy ( part enhancement ). Sometimes, you will define multiple failure modes ( It could have failed because of A or it could have failed because of B or… )

Use the Requirements as a Check List

Identifying What Worked? is as important as defining What Failed? in your design. We accomplish this objective by using our original requirements as a check list:

  • Pulley Spindle Adapter
    • High Friction “press fit” onto the pulley spindle: Worked
    • High Friction “press fit” to the interior of the 5/8″ bearing: Worked
    • Provide outside bearing keeper: Failed
  • Inside Bearing Cover
    • Must not rub against the tension arm: Worked
    • Provide a high friction “press fit” to the outer diameter of the 5/8″ Bearing: Worked
    • Provide a “retaining ring” to keep the bearing confined within the pulley: Worked
    • Provide a “retaining wall” for the drum belt: Worked
    • Mate with the Outside Cover: Concentric end to end mate: Worked
  • Outside Bearing Cover
    • Provide a high friction “press fit” to the outer diameter of the 5/8″ Bearing: Worked
    • Provide a “retaining wall” for the drum belt: Worked
    • Mate with the Inside Cover: Concentric end to end mate: Worked

This is where analysis gets a little tricky: Find the missing ( un-stated ) requirements . In our current design example we missed:

  • Join the Bearing Covers ( Pulley Belt Surface ) so that they do not separate during operation
  • Size the pulley so that the dryer drum will turn with a full load of clothes

We try to give ourselves a break when we miss requirements.

Clearly, we did not miss joining the bearing covers => We did use copper tape. However, we massively underestimated the lateral force the drum belt would apply to the pulley creating a situation where the tape would prove to be insufficient ( in truth the copper foil was sufficient but the adhesive used on the copper foil tape proved to be less than what we needed )

As far as sizing the pulley we did our best to measure the original ( damaged ) part and while we suspected that the drum belt had stretched we had no method to validate our suspicion

We knew we did not know the magnitude of the lateral force that was acting upon the pulley => We hoped our keeper design would be sufficient… and we were wrong

It’s easy to fall into the How did I miss that? trap & waste time Kicking yourself! It is far better to take the emotion out of the design process and simply learn from failure.

Visualizing the Failure

Visualization may be accomplished via a number of processes:

  • Imagination => Creating a picture ( video ) in your mind
  • 2D Drawings => Create sketches
  • Text => Write the story of the failure
  • 3D models & simulations

The visualization method that is best largely depends upon the skills of the designer, the availability of tools and the complexity of the design project.

In Colorado we have additional tools that aide visualization; We have the freedom to torch some shatter on a domeless nail and access the super computer God gave us…. but that’s another story.

For our V1 replacement part design the failure story is simple:

The lateral force the belt applied to the pulley caused the pulley keeper ( both the tri-ring on the original metal spindle and the retaining ring on the spindle adapter ) to fail..

The pulley ( Bearing and covers ) then wandered off of the spindle…

We suspect that their may have been a delay between the keeper failure and the pulley pieces departure from the spindle: The way that the tape was pulled from the inside bearing cover suggest that for some time the outside bearing cover was being held in place by the copper foil tape… As the last bit of copper foil tape was being drawn off of the inside bearing cover a “sling shot” was created which resulted in the thunk…thunk sound effect of the failure.

The fact that the copper foil tape was drawn off of the inside bearing cover tells us that the friction fit between the outside of the spindle adapter and the inside of the 5/8″ bearing was good to great:

The adhesive on the copper foil tape is sticky and we had burnished ( rubbed ) the copper tape down around the entire circumference of the pulley belt surface => The force required to pull the copper tape off of the inside cover was significant and yet was slightly less than the friction force between the spindle adapter and the bearing.

Once the failure visualization seems complete ( accounts for all observable data ) it is time to move forward with re-design.

One aspect of the failure is clear to us: If the keeper had not failed then the pulley would not have split in two => The Copper Foil tape would have been sufficient.

Your Failure Visualization might be wrong: No worries!

You will discover the truth as your progress toward success.

The faster you are able to iterate through this design – test – analyze process the faster you will achieve success. This singular fact is why 3D Printers have found a secure home in industrial design => For prototyping & not manufacturing.

If the professional / experienced industrial designers incorporate failure into their normal design process then so should you…

One of the techniques that we utilize routinely is to load our minds with as much data as possible but then instead of starting the re-design we do something different…. go for a drive… fix a meal… work in the garden…

We have found that for complex challenges it is often necessary to get out of the way and allow God’s super computer to work

Most of the time while we are busy focusing on another task the answer pops into our minds. Not always => But often enough that we recognize the pattern.

True design failure will only occur if you make the decision to give up trying to resolve the challenges you face

Version 2:

Our primary challenges for the V2 Design:

  • Incorporate a beefy / strong spindle keeper into our design
  • Increase the diameter of the pulley to apply more tension to the drum belt & handle those large clothes loads

In our V1 design we implemented a one layer thick spindle adapter keeper because we did not have room on the original metal spindle to implement anything thicker before we encountered the keeper slot on the metal spindle ( we ran out of room ).

The dimensions of the metal spindle had not changed so we needed a new plan that was going to cause us to revisit our assumptions and think a little farther out of the box.

Our V1 design was essentially a mimic of the Maytag create part with modifications to account for the standard parts we had available.

In our V1 Design the pulley diameter was sized to duplicate the original ( damaged ) part. So, while we knew we needed to make the pulley diameter bigger we really had no method to gauge how much bigger?

We don’t really like guessing so we decided to do a little research on belt stretching

Step 1: Conceptualize

When we begin a re-design we do not fire up the 3D modeling tools => We take a step back and:

  • Identify design priorities
  • Review our prior design and identify Why we made design decisions
  • Identify the design challenges
  • Identify research topics

We attempt to ascertain if our architectural construction is flawed => Do we need to make a left turn… abandon our prior design? or veer right… and tweak our prior design?

Reviewing the V1 architecture

By the time we finished the V1 design we had four 3D Printed parts:

  1. Spindle Adapter
  2. Spindle Keeper tri-ring
  3. Inside Bearing Cover
  4. Outside Bearing Cover

And two standard parts: Two 5/8″ bearings

It was clear to us that the 5/8″ bearings were not the problem => worked great!

The problem child in our V1 design was clearly the spindle adapter tri-ring keeper and while we recognized that this could be a material problem ( we were using PLA and we suspected the original was made from nylon ) we decided to make a small left turn and consider all of the methods we had come across for securing rotating objects to spindles:

  • set screws
  • metal pins
  • spring loaded clamps
  • Metal E-rings ( and their cousins )
  • High friction ( hammered on ) end caps
  • Washer & Nut directly on the spindle
  • etc..

It wasn’t too far into this thought process that we began thinking: metal. Any time we encounter the possibility of high lateral force the keeper is made out of metal

Stand on the Shoulders of Giants

Good designers are observant: constantly looking to see how others have solved design challenges.

In your everyday life you are surrounded by solutions: Folks you have never met have solved similar challenges and their genius is on display if you have the curiosity to investigate.

Once we had our 3D Model of the Spindle Adapter modified we ran a few sizing test ( prints ) of the Keeper Holder to perfect the fit of the 0.051″ ( 1.2954 mm ) blue tempered steel wire ( Music Wire ) we had selected for our Keeper Pin.

Spindle Adapter:

When we began the V2 re-design for the spindle adapter we knew we needed to increase the strength of the keeper. We visualized two approaches that we thought would work:

  1. Eliminate the keeper ring on the spindle adapter and create a new beefy keeper ring ( thick clamp washer )
  2. Integrate the tri-ring 3D printed keeper with the keeper ring on the spindle adapter. into the spindle adapter component

We decided to start with option 2 mainly because it would reduce the number of 3D printed components for our replacement pulley.

Our first step was to use Save As and create a V2 Spindle Adapter 3D Model design file.

V2 Spindle Adapter: Dimension Modifications

V2 Spindle Adapter: Dimension Modifications

Getting started was easy: we increased the thickness of the Keeper ring from 0.35 mm to 5 mm ( from one layer in thickness to about 20 layers in thickness ).

…. and then we were stuck => We didn’t know what to do next

Should we use a set screw? … Should we use more than one set screw?… Should we use a different approach for our keeper?

Modeling the “System”

Context is everything => The clothes washer plus the clothes dryer create a clothes cleaning system

The clothes dryer is also a system

Dryer Drum Belt Tension Pulley System

Dryer Drum Belt Tension Pulley System

Within our context the “system” is simple and consists of:

  1. The 3D Printed parts for our replacement pulley
  2. The standard parts for our replacement pulley
  3. The original metal spindle
  4. The original nylon spacer washer ( closest to the metal belt tension arm >
  5. The metal belt tension arm
  6. The drum belt

3D Model of the Metal Spindle and Nylon Spacer Washer

3D Model of the Metal Spindle and Nylon Spacer Washer

We decided to create a 3D Model of the original metal spindle plus the original nylon spacer washer. We created our model based on careful measurement of the spindle with our caliper.

Why? => We have absolutely no intention of 3D printing the spindle…

We wish to visualize our spindle adapter design with the spindle so that we may contemplate keeper solutions

Virtual 3D Assemblies => Visualize Solutions

Assemblies allow the designer to load multiple parts into a single view and constrain the parts relative to each other.

3D Assembly Spindle Plus Spindle Adapter

3D Assembly Spindle Plus Spindle Adapter

Simply visualizing multiple parts together may not appear to be interesting upon first inspection. In our current design example we created a cross-sectional view through the axis of the spindle’s length:

3D Assembly Spindle Plus Spindle Adapter: Cross-Section View

3D Assembly Spindle Plus Spindle Adapter: Cross-Section View

As we were examining the cross-sectional view the answer to our keeper dilemma suddenly became obvious => Pins through the Spindle Adapter that intersect with the keeper notch on the original metal spindle.

One aspect of our solution exploration that we have not discussed is critical: We took a walk through our inventory of standard parts to look for possible solutions:

  • Did we have set screws?
    • What sizes?
    • How many?
  • Did we have pins?
    • What sizes?
  • What else did we have in stock that might work?

We loaded our brain with inventory prior to launching the 3D editing tools. This is a good trick to use even if you are not dealing with an infrastructure crippling catastrophe => Avoid spending money on “new things” and “use what you have”

Walking through the web looking for possible solutions is also a good technique for discovering which standard parts might be useful to stock…

If you are blessed with good fortune we also recommend asking your local farmer if you could take a walk through their shop => Gather some clues from the original preppers

Our 3D modeling tools allow us to edit parts from within the context of the assembly view ( An extremely powerful capability ).

3D Assembly Spindle Plus Spindle Adapter: Adding Keeper Pin Holes

3D Assembly Spindle Plus Spindle Adapter: Adding Keeper Pin Holes

Reference Geometries: Using features on One Part to create features on Another Part

In our current design we want to use the notch on the Spindle as a reference for creating a pin slot feature in our Spindle Adapter.

Note: You don’t need an Assembly => The Assembly makes the design task easier

We needed the Assembly to allow us to think through how we were going to implement our keeper

We could have simply sat down with paper, pencil & ruler and created the sketches we needed to help us think through our design challenge => Old School. Our CAD tools simply made this process easier

We do not consider 3D Assemblies a must have CAD tool requirement.

We do recognize that establishing tool requirements is a debatable topic. Here are our thoughts:

  • CAD tools that support Assemblies and a useful collection of design capabilities are generally more expensive
  • It is possible to solve all design challenges without 3D Assembly capabilities

…on the other hand…

We use 3D Assemblies frequently and they are extremely useful and greatly reduce the time we spend creating 3D models => If you have the budget, we do reccomend adding Assemblies to your 3D CAD tool requirements shopping list.

0.051" Blue Tempered Steel Wire ( Music Wire )

0.051″ Blue Tempered Steel Wire ( Music Wire )

After perfecting our 3D model with a few test prints to size our keeper pin holes to fit 0.051″ ( 1.294 mm ) diameter blue tempered steel wire ( Music Wire / Spring Wire ) we 3D Printed the V2 Spindle Adapter.

We chose to use music wire to fabricate ( cut & bend ) our keeper pin because:

  • We stock Music wire as one of our standard parts
  • Music wire is relatively inexpensive
  • Music wire is extremely strong

We stock blue tempered steel both as wire ( round cross-section ) and ribbon ( rectangle cross section ) after we found it to be extremely versatile. Our stock includes a variety of dimensions.

We were clued in & turned onto Spring steel by one of our local farmers after he graciously allowed us to take a walk through his shop. He had a huge inventory of spring steel which spurred a long conversation about how he used it.

Why is Spring steel called Music Wire? => Look Here

V2 Spindle Adapter Plus Keeper Pin

V2 Spindle Adapter Plus Keeper Pin

V2 Spindle Adapter: Keeper Pin Installation

V2 Spindle Adapter: Keeper Pin Installation

Inside Bearing Cover:

The re-design of the 5/8″ Bearing covers centers on one requirement:

  • Increase the diameter of the pulley to take up the slack created by the drum belt stretching ( due to use )

We began our re-design by researching dryer drum belt stretching. As you might imagine, this is not a topic that appliance repair suppliers have put much energy into as they prefer to sell new dryer drum belts. However, perseverance paid off and we found some useful data in the Questions and Answers section of one of the appliance repair parts suppliers websites.

The belt tension system is designed to take up 1/2″ to 3/4″ ( 12.7 mm to 19.05 mm ) of drum belt stretching. Since our V1 dryer repair worked for small, medium and large clothes dryer loads and failed for heavy super clothes dryer loads we concluded that our drum belt stretching was likely at the lower end of the stretching range => 1/2″

Based on our research we decided to work in increments of 10 mm to resize the diameter of the pulley

In the V1 design we didn’t have much room to implement the pulley’s belt surface as the outer diameter of the 5/8″ bearings was roughly ( the original part was damaged ) equivalent to the diameter of the original belt tension pulley. The lack of room caused us to implement the pulley design using a simple butt joint that we secured with copper foil tape ( which proved to be less than ideal in operation ).

The increase in the pulley’s diameter allowed us to re-think our part assembly plan: We decided that having a single solid belt surface across the entire pulley width would be far superior.

V2 Pulley Bearing Covers Re-design Concept: Plug-in Covers

V2 Pulley Bearing Covers Re-design Concept: Plug-in Covers

Our re-design plan is simple: Using a plug together pulley design we will be able to glue the Outside Bearing Cover to the Inside Bearing Cover greatly improving the strength of the V2 pulley. We will continue to cover the belt surface with copper foil tape but now the function of the tape is simply to provide a long wear surface for the belt to ride over.

Our first step ( as always ) was to use Save As to create a V2 Inside Bearing Cover 3D Model file.

Once we had a re-design plan the Inside Bearing Cover re-design required only one modification:

  • We increased the diameter of the pulley belt retaining wall
V2 Inside Bearing Cover Design Changes

V2 Inside Bearing Cover Design Changes

A Record of Changes

You may have noticed that we go to great lengths to document our design changes. What may be subtle is that we consider documenting what did not change as critical as what changed.

Normally, we create a text ReadMe file in the file system directory containing our 3D model files containing:

  • Design Version Labels
    • Requirements
    • Planning Notes
    • Research ( critical data plus links to source )
    • Design Changes ( including No Change )
    • Pass / Fail observations

This document is an elaborated form of our normal ReadMe file.

Create History or be Doomed to Repetitious Failure

Design Journal

Design Journal

The act of creating design journals may appear to be unwarranted overhead ( extra work ) while you are working on a design. However, while you are working on the design the information is fresh and easily expressed… a week from now, a month from now, a year from now … in the future… you will revisit one of your designs and ask the inevitable question: What was I thinking?

We are including this observation for the young bucks and does as we old geezers are painfully cognizant of the limitations of human memory.

Any design process, even one as simple as creating a pulley, is filled with a myriad of decisions. Those decisions evolve into knowledge as the design matures ( as decisions are tested ). We find the act of committing design decisions into journal from triggers retention and evaluation

For Example: We expected the V1 Spindle Adapter Keeper to fail. The certainty of the failure was triggered when we wrote:

The Spindle Adapter Keeper is one layer thick

That was one of those Duh! / Of Course! / Oh shit! moments. We have a ton of experience with one layer thick 3D Printed structures and we know they are flexible and have a tendency to shear / peel away from whatever they are attached to. That sudden clarity caused us to reflect on another piece of knowledge we have developed over the years:

When you are in the process of making design trade-off decisions attempting to solve a challenging obstacle the mind is capable of rationalizing crazy ideas…

Upside ( after we finished kicking ourselves ): We began contemplating an improved keeper design a week before the V1 design failed…

If you were a corporation you would refer to this knowledge as Intellectual Property ( IP ).

Creating a design journal need not be a laborious task: jot down some sketches and create some notes…. Record a quick video or audio notes… etc…

Creating Design Journals is an extremely friendly act to your future self as well as for family members, friends and maybe a few strangers => Our hope for this article…

Inside Bearing Cover

Inside Bearing Cover

Outside Bearing Cover:

V2 Outside Bearing Cover Design: Inside Bearing Cover Socket

V2 Outside Bearing Cover Design: Inside Bearing Cover Socket

The Outside Bearing Cover required two design alterations:

  1. Increase the diameter of the Belt Keeper Wall
  2. Create a new pulley belt surface that:
    • Has an increased diameter ( 10 mm )
    • Provides a socket for the Inside Bearing cover to be plugged into
    • Provides a solid belt surface across the entire width of the pulley

Once again, we began our modeling task by using the Save As command to create an independent 3D model design file from the V1 source.

V2 Outside Bearing Cover Design: Dimensions

V2 Outside Bearing Cover Design: Dimensions

3D Modeling Steps

We created the stepped Outside Bearing Cover using three sketches and three extrusions ( boss operations ).

The first sketch is the Bearing Retaining Ring and the Belt Retaining Wall => This is a short, wide cylinder.

V2 Outside Bearing Cover Design: Retaining Ring / Wall Platform

V2 Outside Bearing Cover Design: Retaining Ring / Wall Platform

The second sketch created the V1 pulley belt surface cylinder with thin ( 0.8 mm in V1 and 1.0 mm in V2 ) walls and a 10 mm height.

V2 Outside Bearing Cover Design: V1 Belt Pulley Surface

V2 Outside Bearing Cover Design: V1 Belt Pulley Surface

Why the change in wall thickness from the V1 design?

To provide a socket for the Inside Bearing Cover to plug into

By increasing the wall thickness from from 0.8 mm to 1.0 mm we provided a 0.2 mm gap between the Inside Bearing Cover and the interior of the Outside Bearing Cover socket. A 0.2 mm gap is equivalent to one half of the nozzle diameter ( 0.4 mm ) => In our experience this provides a high friction slip fit: Parts will go together without the aide of a press ( or hammer ) and will remain in position.

We dimension our designs the way we are thinking about the design: In this case we were thinking about wall thickness. We could have simply set the diameter of the outer sketch circle to:

Diameter = 41.2 mm + ( 2 * Wall_Thickness )

However, this is not how we were thinking about the design. Instead we:

  • Created two vertical reference lines
  • Constrained one of the vertical lines as a tangent to the interior sketch circle
  • Constrained one of the vertical lines as a tangent to the exterior sketch circle
  • Set the dimension between the two vertical lines at 1 mm ( One Wall_Thickness )

V2 Outside Bearing Cover Design: Setting Wall Thickness

V2 Outside Bearing Cover Design: Setting Wall Thickness

It is a little more work but this is one of the ways that we help ourselves document our thought process as we are creating the design => Part of our documentation strategy.

The third sketch created our V2 pulley belt surface cylinder that has thick ( 5 mm ) walls and a 22 mm height.

V2 Outside Bearing Cover Design: Full Width Pulley Belt Surface

V2 Outside Bearing Cover Design: Full Width Pulley Belt Surface

More about 3D CAD Tools

Did you notice that we created our third sketch on a new plane?

Good design tools allow the designer to select a design feature and use it as a reference for generating new reference planes and axes.

The ability to insert new planes and axes is a required 3D Model CAD tool feature

V2 Outside Bearing Cover Design: New Sketch Plane

V2 Outside Bearing Cover Design: New Sketch Plane

We needed the new plane so that we could create a constrained relationship between a circle in a new sketch and an existing feature in the design => The V1 Pulley Belt Surface.

The reference feature does not exist on the X-Y plane

We spent some time describing our modeling approach for the Outside Bearing Cover because there is always more than one way to create any object model:

We could have created the platform, created one thick pulley belt surface cylinder the full width of the pulley and then cut out our socket for the Inside Bearing Cover

We could have created a profile for the pulley and then revolved it around an axis to create the complete pulley with one sketch and one revolve extrusion ( an advanced technique )

There is not a best modeling method: As you gain experience with your 3D CAD modeling tools you will find that experimenting with object creation methods will allow you to reduce your design effort or create difficult structures ( our current design is a simple object structure )

V2 Outside Bearing Cover Design: Fit

V2 Outside Bearing Cover Design: Fit

While it is not obvious in our diagrams the bearing covers are one printer layer ( 0.25 mm ) short of the width of the two 5/8″ bearings allowing us to apply compression to the covers during the assembly process ( and eliminating any lateral freedom of movement ). We achieved “perfect fit” after a couple of test prints.

V2 Outside Bearing Cover

V2 Outside Bearing Cover


V2 Dryer Belt Tension Pulley Components

V2 Dryer Belt Tension Pulley Components

The V2 assembly process is similar to the V1 assembly process:

  1. File the interior of the spindle adapter to eliminate the seam
  2. Apply copper ( or aluminum ) foil tape to the exterior of the spindle adapter to eliminate the seam and provide a long wear surface and perfect fit ( with the interiors of the the 5/8″ bearings )
  3. Stack the two 5/8″ bearings into the Inside Bearing Cover
  4. Apply a bead of hot glue to the Inside Bearing Cover near the root of the Bearing cylinder
  5. Press fit the Outside Bearing Cover onto the 5/8″ bearing and the Inside Bearing Cover ( Compress gently to remove any lateral space within the pulley )
  6. Clean up any hot glue ooze with a sharp X-Acto knife
  7. Apply copper ( or aluminum ) foil tape to the Pulley Belt surface
  8. Insert the Spindle Adapter
V2 Dryer Drum Belt Tension Pulley: Assembly

V2 Dryer Drum Belt Tension Pulley: Assembly

Notes: Hot Glue

Hot glue:

  • Creates a strong bond with PLA parts… but not too strong
  • Great at absorbing shock and vibration
  • Easy to remove with Isopropyl Alcohol ( Rubbing Alcohol )
  • Easy to trim with a sharp blade ( X-Acto )

Notes: PLA Filament

PLA is a modern miracle plastic:

  • Made from corn ( and other plants )
  • Biodegradable ( when exposed to UV / Sun light )
  • Recyclable ( at least in theory => economics makes this tricky )
  • Impervious to most chemicals ( except dangerous organic solvents )
  • Strong => Stronger than ABS
  • Relatively low melting point: 150 to 160 °C (302 to 320 °F )

We like working with PLA => makes us feel green all over

In our design we don’t know if our current design is going to work: Is the pulley diameter large enough to take up the slack of the stretched dryer drum belt?

If the answer is NO then we will need to increase the diameter of the Outside Bearing Cover and we might be able to reuse all of the other components.

The idea that we might need to take the V2 pulley apart occurred to us before we began assembly => And hot glue provides a good trade-off: strong but not too strong and easy to remove by soaking in a bowl of Iso…

Hint: Use a small diameter nozzle hot glue gun

We use hot glue frequently for a variety of tasks and have collected a couple of hot glue guns. When working with smaller 3D Printed objects we reach for our detail hot glue gun.

Detail Hot Glue Gun

Detail Hot Glue Gun


V2 Pulley Installed

V2 Pulley Installed

We pressed the pulley onto the original metal spindle with our hands as far as we could ( about 75% ).
3D Printed Spindle Adapter Seating Tool

3D Printed Spindle Adapter Seating Tool

We then used the Spindle Seating Tool we made with the V1 design and a hammer to tap.. tap.. the pulley until it was fully seated on the spindle.

Out last step was to press the metal keeper pin into place by pushing it through the keeper until the ends of the keeper pins were visible on the opposite side. The keeper pin was a little stubborn / difficult when it encountered the metal spindle => We had to use pliers to force it in.

Once the metal keeper pin was fully engaged we slightly bent the metal keeper away from the pulley to prevent any rubbing.

One fact became obvious: The V2 Pulley is not coming off of the metal spindle unless we remove the metal keeper pin!


Our clothes dryer is back to being a work horse!

It’s been running for a couple of months without any issues.

We have two concerns:

  1. Continued stretching ( or breaking ) of the dryer drum belt: Will we need to create a V3 Pulley design to take up more belt slack in the future?
  2. Heat => Long term viability: The dryer drum belt tension pulley is operating in a warm environment: Will the temperature exceed the PLA deformation temperature?

Only time will provide the answers to those questions but since the pulley hasn’t failed in the first two months of operation our Heat Concern has been greatly diminished => We have dried quite a few loads of clothes with the heat setting on high…

Success is rarely a permanent condition

While we are very pleased with our dryer repair efforts the best we are able to claim is Success for now.

Fortunately, we have a 3D printer and we know how to use it!


There was a time in history when there was no such thing as a Prepper or, and likely more accurately, everyone was a Prepper. The concept Be Prepared was more than the Boy Scout motto it was the reality of our existence.

We didn’t pull any punches in our description of the 3D printing process: It’s not all that difficult but it is not trivial. The biggest obstacle you will face is overcoming the idea that you can’t do it => Of course you can do it!

We believe the ability to overcome daunting tasks is inherent within all Preppers => When you consider the number of challenges that one must face preparing for a future where you are cut off from the infrastructure of civilization: 3D Printing is easy.

3D Printing is relatively new ( at least at affordable price points ) and we suspect that many Preppers have simply never considered adding 3D Printing skills to their preparedness plans.

Our Dryer Repair was a trivial example but it allowed us to walk through all of the steps in the 3D printing process including 3D model design. More importantly, it provides a great vehicle to explore some fundamental preparedness concepts like What to stock?. Having a 3D printer ( and the skills required to use it ) will greatly reduce the diversity of items to stock and allow for greater flexibility in dealing with whatever challenges may arise.

We have not explored the aspect of 3D Printing that initially attracted us: The ability to design and implement new things. We use 3D Printers to design and implement everything from Toilet Paper Holders to fully functional Printed Circuit Boards. For us, the idea of using a 3D printer to repair the dryer by creating a replacement part was new but not strange.

Our Recommendation: Don’t wait => Start building your 3D Printing skills now: Prepare. By engaging now not only will you develop a valuable skill set you will start re-thinking your preparedness stocking plan which will result in significant financial savings ( standard parts are less expensive than “purpose specific parts”) => Wood is cheaper than a table made from wood.

…And… in the event that civilization does not encounter any cataclysmic events in your neighborhood you will have relevant skills for the advancing Robot Invasion of the work place… Robots are inevitable.

How societies choose to leverage Robots is a decision:

  • When robots are used to improve the lives of People than robots are good
  • When robots are used by faceless global corporations to subjugate, impoverish and replace People in the relentless pursuit of increased profits than robots are bad

Here is a fact we stumbled across in our research: Industrial robots have an operational cost of ( about ) $0.75 / hour… and the operational costs are falling… This fact has been completely overlooked by populations demanding an increases to the minimum wage => Increasing the minimum wage is simply expediting the motivation for large corporations to adopt Robot replacements for low skill work.

The same argument applies to immigration: Low skill jobs will be staffed by robots. The arguments that countries need low skill immigrants to do the work that high skill people refuse to do is completely false ( it is an intentional misdirection so that communities don’t have the conversation about the proper role of robots in our evolving civilization in our opinion ).

Robots are a threat

The current path of robot deployment is clearly aligned with the faceless global corporations attempting to subjugate, impoverish and ultimately kill the majority of the People on the planet.

Yes, we are certain that some will accuse us of being Conspiracy Theorists propagating Fake News. That’s OK => We really have no interest ( On this website ) attempting to convince anyone of the results of our analysis of current technology trends: If you get it we are here to help… If you don’t get it then it is up to you to do the research and contemplate your own survival ( both economic and organic )

Our view is simple: Robots must be controlled by individuals & family businesses & local community businesses and not trans-national ( globalist controlled ) corporations. We believe in Localism / We believe in Individual Liberty

We have nothing against international trade or sharing with our brothers and sisters around the globe. In fact, we publish world-wide to facilitate localism everywhere. Localism is about promoting People: To live in liberty and strive for their dreams.

The natural reaction to the robotic revolution ( akin to the Agricultural Revolution, Industrial Revolution & Information Revolution ) for many people is to become anti-robot. From our perspective this is not a sane conclusion: It’s like saying you are anti-hammer, anti-lever or anti-wheel.

Robots are tools. Supposedly, homo-sapiens are the dominant species on the planet because we learned how to use tools. ( We view that argument with suspicion: It is our ability to imagine and manifest our dreams into our reality that we feel is the key differentiation )

3D Printers are robots… and so is your dish washer, clothes washer, clothes dryer, rice cooker, bread maker, etc.. You are surrounded by robots…

3D Printers may be used to create new robots

Either we will choose ( as a community ) to be subjugated by robots or we will choose to subjugate robots to our will

We hope that this article has provided evidence that you may be a master of the robots and specifically, that adopting 3D Printers into your daily existence is a survival trait

If you have slogged through and read this article to this point we are confident in claiming that you too, have the intelligence required to become a 3D Printing expert. Yes, it will take a little time but the path is fun as you create unique objects that will make your life better.

Article Construction as a Single Post: Why?

We wrote this articles to help Preppers who plan to survice an infrastructure calamity: including the loss of the internet.

By creating a single ( long ) post we have made printing and storing this article trivial ( one Print operation ). This may seem like a trivial concern but we do think through our objectives and make plans to promote our objectives ( and this was one aspect ).

CAD 3D Modeling tools without the Internet

Good 3D modeling CAD tools are relatively expensive: It is reality and we hope that this fact eventually dissolves as CAD tools are adopted across a mass-market.

Many CAD tool suppliers are attacking the cost barrier by:

  • Creating Subscription CAD tools ( monthly or yearly licenses )
  • Creating Cloud CAD tools ( Internet must be available )

Any CAD tool that is Cloud Based or has a subscription licensing model is unacceptable from the perspective of aiding a Prepper as either condition may prevent CAD tool usage when the CAD tool is needed most.

Advertisement: Why You Should Purchase Your 3D Printer from Krakatoa Ranch

Our goal is to make you ( or your business ) successful using 3D Printers to meet your goals.

We create professional grade 3D Printers by starting with the highest quality 3D Printing kit available ( Designed and Manufactured in Oklahoma ) and we enhance / upgrade the printer as we build it to minimize maintenance.

Once the 3D Printer is fully assembled we tune it and calibrate it so that it delivers top quality printed objects with accurate dimensions.

More Importantly: We provide on-site training, tuning, calibration and maintenance for one year at a rock bottom labor cost to maintain your 3D Printer while we provide the knowledge and skills that will allow you to keep your 3D Printer operating for years.

Krakatoa Ranch Fused Filament Extrusion ( a.k.a. DFM ) 3D Printers are designed to print objects day after day

All of our 3D Printer customers also have free access to all of our published 3D models ( for personal use )

…and… any 3D Models we publish in the future

View our 3D Printer Solutions Overview Brochure

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