The On-Line Magazine of Rideable Model Railroading

  NUMBER 149

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© March 21, 2010   

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Show Me That Profile
(Some Whys Behind the Wheel)

 

Written by Carlyle (Carl) Rossow

 

There are many different styles and approaches for making train wheels.  This article is not intended to suggest one method over another.  It is intended to give some food for thought about how the wheel profile should be on the finished wheel.  I will save my method of making wheels for a future article.

What Radius?

Whatever method is used, there is one step in the process that sometimes gets overlooked.  It is putting a radius or a chamfer on the outside corner of the wheel.  This is a very important part of the wheel.  Sadly a lot of blue prints of wheels show this corner to be sharp.  Most of the documentation available for model wheel standards leaves out any mention this step.  Even though the IBLS standards (FIGURE 1) that are used by many clubs show there is a radius on the outside corner of the wheel, it does not give any tolerance or instruction about size of the radius.  Furthermore, since no information is given for this corner it is sometimes left sharp.  Taking all of this into consideration, it is no wonder why wheels with sharp corners are turning up more frequently.  This is not a conspiracy that needs a Presidential Czar appointed to monitor model train wheel standards.  It simply is an oversight.

 
FIGURE 1

Before continuing the author would like clarify two things. 1. Typing is not my thing, in fact, if I have to answer an email with more than a one-word answer, I will probably just pick up the phone and call, and 2. I prefer a radius on wheels compared to a chamfer.  So to save time and my fingers this will be the last time I will type the word “chamfer” in this article.

So why is this step so important?  A young machinist apprentice was told once,” Unless the part being made is intended to cut something, never leave a sharp corner.”  Sharp corners on wheels cut into aluminum and steel rail.  The primary reason for the radius is to help prevent or greatly reduce large gashes in the rail caused from derailments.  So in other words,” one small step for wheel makers, one giant leap for track crews.”  Also an unintended benefit for a radius is the prevention of cut fingers trying to put derailed equipment back on the track.  I know the goal is to have no derailments, but it does happen.  So from a maintenance and safety stand point a radius is a good thing.  Lastly, I think it makes the wheels look better too.

How big should the radius be?  Well that is the $64,000 question isn’t it?  Here’s my attempt to answer that question.  A good start for standard gauge wheels would be a radius of .040 +/-.010.  With the wheel turning in a lathe and using a good sharp course file this can be done quickly with just a few stokes.  If you have narrow gauge wheels go bigger if you prefer.  Everything with narrow gauge is BIGGER.  The bottom line to all of this is any radius is better than no radius.

Flanges, Fat or Skinny?

This next part of this article is a story of trial and error.  The flange on the wheel is another place where more information is needed.  When looking at the drawing of the IBLS standards (FIGURE 1) there are some dimensions that are left up to the discretion of the person making the wheel.  The interpretation of these dimensions will make a big difference in how the end profile of the wheel will look.

One dimension missing is where to end the 10-degree angle on the inside of the wheel.  Another is the radius on the outside diameter of the flange.  The last dimension left out is where the .094 radius blends with the outside 10-degree angle.  Even though the last two dimensions are left out, let’s just focus on how the first dimension to see how it can affect the entire wheel profile.

Illustrated by FIGURE 2 are two scale profiles of standard gauge wheels.  It is easy to see that the flange on A is much more narrow than B.  I have to apologize for what might sound like a Sesame Street lesson, but this is what can happen when dimensions are left to artistic license.  Both wheel profiles will pass any IBLS inspection because they are both within the tolerances given.  Furthermore, both will perform well on any private or club track that uses IBLS standards.  The reason I know this is because FIGURE 2 is an illustration of wheel profiles that can be found on equipment my dad built, and in all these years there has been no problems with either profile.  When my dad started his first steam engine back in 1976 his wheels had the narrower flange and he never really liked how sharp the flange come out.  He also didn’t like that the flange was not centered.    This is illustrated in FIGURE 2 on profile A.  The .123 chord length in not centered with the .156 flange width.  Building your first engine can be like raising your first child.  You realize all of the mistakes you made.  The good news is, that in both cases, every mistake you have made can be fixed with time, work, patience, and love.  The mistake here is more of a matter of preference.  

 
FIGURE 2

As we all know in this hobby things wear out and one of those things are wheel flanges.  Building things so they last longer to cut down on maintenance is always the goal.  Dad knew this and that is why he wanted a big fat flanges.  Once he realized that by just changing the length of the 10-degree flange angle on the inside of the wheel from .187 to .093 would give him a fatter flange, he started making all his wheels that way.  Also this solved another problem by centering the flange.  Even though the width dimension of both flanges in FIGURE 2 are .156 wide, the difference gained in width comes from the chord length of the outside radius.  The outside radius increases from a .060 radius to a .070 radius.  That changes the chord length from .123 to .142.  That might not seem like much, but that is .019 more wear gained which equals longer wheel life.  Just because the enlarged illustration makes the flange difference easy to see, trust me, it is easy to see the difference on an actual wheel too.

Steel, Tool Steel, or Cast Iron?

I know this is more of a side bar to what the article first started out as, but I think I should throw this into the mix too.  The choice of material to use for wheels is another consideration.  It does dovetail into the subject of the performance and the life of the wheel.

When Maricopa Live Steamers moved to their new home out by the Adobe Mountain Dam in the summer of 1999 one thing became very apparent quickly.  Not all cast iron wheels are created equal.  Most of the branch line runs at the Adobe Western Railroad are quite long.  It is very easy to wrack up a bunch of miles on equipment.  In no time many of the cast iron wheels had the flanges completely worn off and we had a few scary derailments caused by this.  For this reason the club has since converted all its rolling stock over to steel wheels.  

There are tons of cast iron wheels roaming around world in this hobby and a lot of them have proven service records.  The point I am making is that if the cast iron is lacking in its metallurgy it is possible to get poor service from the wheels.  We found this out at MLS.  The cast iron wheels we got from a vender just didn’t have what was needed to make good wheels that would last.  Recently some venders have even stopped offering cast iron wheels due to the poor service records.  I am not an expert in the field of metallurgy and I was relieved the day I got my “A” and past that subject in college knowing I would never have to take it again.  I know there are things that can be put into a foundries witches brew to improve the properties of cast iron; I just don’t know exactly what they are and have no interest in doing the research to find out. 

In defense of cast iron castings, they do have the appeal of giving the wheels a much more accurate prototypical profile such as spiral-backed wheels.  If you want this level of detail then perhaps putting steel tires on the wheels might be an alternative to insure good wheel life. 

In my opinion steel is the safer choice when it comes to wheel life.  For the most part, it really doesn’t mater what steel is used just as long as different steels are not mixed on the same axle.  What I mean is, don’t press a wheel made from 1018 mild steel on an axle that has a 4140 tool steel wheel pressed on the other end.  The wheels will not wear the same because they are not same material.  This can cause problems down the road.  I actually saw a great example of this when I visited the Apache Railroad in northern Arizona.  Sitting off to the side in their service yard was a condemned set of wheels.  Cast into each side of the wheels was the material each wheel was made of.  One wheel was labeled 1018, and yes, the other wheel was labeled 4140.  The flange was almost completely gone and the tire was considerably worn on the 1018 wheel.  The 4140 wheel looked as new as the day it was pressed on the axle.  Because the tire diameter of the 1018 wheel wore much faster it caused the flange to rub against rail causing it to wear out faster.  This can happen in our hobby by mixing different grades of steels, which will cause derailments.

I know that this hobby, just like other hobbies, has its fair share of scroungers.  Most of us would probably love to have a junkyard in our back yard.  I have scrounged all of my wheel material.  I have used 1018, 1045, 4130, 4140 and 8620 steels for wheels.  All of these steels work great and are easy to machine.  One bad thing I have found about scrounging material is it can get you into trouble.  You may end up with something like a piece of M2 High Speed Steel.  It was supposed to be 4140.  I bet it would make fantastic wheels that would never wear out, if I had a band saw that could cut it.  When it comes to a piece of steel bar stock that I am considering making wheels out of, I basically have one rule; if I can’t get two wheels out of the same piece of material I will not make wheels out of it.  This way both wheels are made of exactly the same steel.  I label the wheels as a set and they never get mix with any other wheels.  I apply this same rule to making tires.  The two tires must come from the same piece of material.  Last thing, there is one exception to this rule; when making wheels or tires for wheels, if the wheels are powered, the material must be the same for all the powered wheels.

Authors Notes 

Shortly after writing this article, I came across a really great article on DSL by Tom Bee titled “Derailment, Staying on Track” Issue 77.  He covers many other factors that need to be considered from trucks to car design.  On the drawing of his wheel profile he shows a radius on the outside corner with a given tolerance called out.  His wheel profile also has big fat flanges.  I like it.

 

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