Possible Solution For Cracked Axle Gears...Thoughts???

Model Railroader General Discussion (Model Railroader)
21

Seems to me the problems with these gears cracking over time is due to the selection of the original plastics used. POM or the more commonly used acetal are used in gears due to cost, dimensional stability and lubricity.

There are two types of acetal (as well as most polymers) homopolymer and copolymer. Duponts Delrin is a homopolymer and they were first to market. The homopolymers are inherently less expensive than copolymers, are stiffer and are subject to cracking and crack propagation over time.

Copolymers do cost $0.10 or so per pound more, have a lower modulus, are therefore more forgiving to cracking over time.

Manufacturers could do everyone a favor and specify any of the many unfilled copolymers available instead of the historically used homopolymer.

Just a thought…

22

Versatile Plastic material at Shapeways is plenty tough. All you need is a 3D CAD design of the part. Athearn 40023 is the part number of the old outside frame drive wheel assembly. You can get wheels sets from Northwest Short Line that fit the newer gear.

23

Hello All,

This seems to be the crux of the problem.

Thank you for the recommendation on printing material.

According to the original Athearn Assembly Instructions included in the box of the unit I am attempting to rebuild 41023/24 are the Truck Units for the Powered Locomotives. It also notes that the 41022 units are for the dummy locomotives.

The 40023 wheels sets are used on the F-7, GP-9, GP-30, GP-35, SDP-40, SD-45, and the SW-1500 Cow & Calf according to the original documentation.

Thank you for your suggestions.

Hope this helps.

24

40023 is the complete wheelset, 2 stub axle wheels and the gear. You don’t need all that if just the gear is cracked. And those are definitely the older outside bearing truck type. If your loco has the bronze bushings between the wheel and the truck sideframe, those aren’t the right gears, the ones you need should still be available. The whole truck can be repalced if you have the older ones - the plastic sideframes are much nicer than the old metal ones anyway. Far as I know, th only old Athearn BB loco that never got changed over was the Trainmaster, probably because of the uinique offset 3 axle trucks.

–Randy

25

Hello All,

I’ve searched the Athearn/Horizon Hobby (Athearn’s parts supplier) to no avail.

Not to be facetious but…where?

If you have a known source I’m all ears!

The tabs on the truck assemblies I am dealing with extend farther into the frame than the assemblies currently available.

I don’t believe that the newer truck assemblies will fit the frame I have without major modification to the frame.

Athearn does offer HO Drive Axle Gear [ATH60024]. These might work for the cracked gears.

However, I still have the cracked Bachmann worm gear couplers to contend with.

Again, thank you for your suggestions.

Hope this helps.

26

Maybe try the Bachmann Forums.

Mike.

27

Hello All,

I am a member of the Bachmann Forums.

The problem is…

Bachmann has admitted that the plastic couplers between the metal worm gear shafts and the dog bone drive shafts are only available as a part of a major sub-assembly.

Which are currently “Unavailable”.

The reason I began this thread was to explore the possibility of having these unavailable replacement parts replicated by 3D printing.

Thank you for all your suggestions and comments, keep them coming, and…

Hope this helps.

28

I’d be at least mulling over the idea of lost-wax (or maybe even lost-foam) casting.

Make it in metal, cross-drill and insert pins of correct dimensions for the pivots. It will not shear, it will not break, it will not twist or distort.

29

OK, so do the Shapeway, or what ever printing thing you have found. or want to do.

Simple. Just do it.

So far, nobody has jumped up, that does 3D printing, and said " Hey JJ I can do that!"

So search it out. all of us that have responed to your post have given you the resources that have been “go to” places to find what you want.

So, go for it, and explore. [swg]

Mike.

30

Contact James at James train parts. He has made several replacement gears for primarily n gauge but can whip it out in no time if he wants to produce it.

31

He has a ‘shop’ on shapeways.com, or a site with resources here.

32

Hello All,

Excellent resource!

Thank you for the link.

I just reached out to him in regards to both parts.

Hope this helps.

33

Hello All,

I contacted James at James train parts for a consultation on 3D printing for the parts I need.

Unfortunately, he is located in the U.K.

Noting wrong with overseas sources but the cost of tooling, printing, and shipping is currently cost-prohibitive.

I took another look at the solutions A-Line offers. I’ve ordered three components that might work:

  • #12033 - Worm Couplings
  • #40005 - Replacement axle gears
  • #12053 - Brass Sleeve 2mm diameter X 3/32 OD (4 ea) Used to convert 3/32 " ID flywheels to fit 2mm shafts.

I have several A-Line Universal Coupling Kits. The problem is the couplers are designed for a 3/32-inch shaft while the Bachmann shafts are 2-mm.

With the addition of the Brass Sleeves hopefully, I can finally find a solution to the failing Bachmann components.

So far, every Bachmann GP series worm gear coupler in my roster has failed and needed replacement. I’ve gotten proficient at quickly replacing this defective part, but only when replacements are available.

Currently, Bachmann only offers a complete powered truck. The Gear Tower is listed as “Out Of Stock”.

I will keep all of you informed of my progress and will hopefully provide others with a viable and permanent solution to Bachmann’s shortcomings.

Hope this helps.

34

The “worm couplers” are simple Hooke’s joint universal joints. I doubt these could be 3D printed as assemblies. (Cardan is a single joint, Hooke’s are two Cardan on one shaft, apparently, I’ve always called them Hooke’s)

A length of suitably sized silicone hose could perform the universal joint function. Not sure why these plastic Hooke’s joints are ubiquitous but they are.

The function is to take rotational motion that is not perfectly in line and translate it to some angle. The more acute the angle the less satisfactorily a Hooke’s joint performs. Constant velocity joints work better at sharper angles (Birfield Rzeppa). You’re not going to see one of those on a model locomotive.

Two (Cardan) Hooke’s joints in series behave as a constant velocity joint except for rotational imbalance of the intervening shaft itself. Compact double Hooke’s joints have been devised. The angle of rotation of model locomotive driveshafts is not acute enough to present these problems, plus the delivered torque is minuscule.

35

Hello All,

Thank you for your input.

On the HO scale Box Cab locomotives I have restored they indeed use a piece of silicone tubing as the linkage from the motor to the drive mechanism.

The I.D. of this tubing seems to be an uncommon size.

When I went to the service department of the original Caboose Hobbies in Denver, the spry old gentleman- -with a slight German accent- -produced a spool of the sought-after item.

Written on the side of the spool was, “DO NOT SELL!”.

He mumbled to himself, “Vell, OK.”

He asked me how much I needed. Then snipped off about a 6-inch segment from the spool.

When I asked him, “How much do I owe?” With a wink he replied, “It saz “DO NOT SELL!” zo I give it to you.”

In these Box Cabs there is only about 1/16 of an inch distance between the motor and the drive mechanism.

They also run at an extremely slow speed so the torque applied to the tube linkage is minimal compared to the Bachmann GPs I’m dealing with.

Another aspect of replacing the O.E.M. linkage with a piece of tubing is the driveshaft (dogbone) has horned ball ends.

Between the horned ball and the main section of the shaft there is a 1/8-inch reduced section.

This section would need to be removed, thus adding to the length of tubing needed and increasing the twisting of the tube under load.

If I only remove the horns on the ball and push the tubing over it I’m afraid there wouldn’t be enough contact area of the ball for a secure connection.

As Albert Einstein was quoted as saying, “When you open a can of worms the only way to get all the worms back in the can is to use a bigger can.”

Because this p

36

"As Albert Einstein was quoted as saying, ‘When you open a can of worms the only way to get all the worms back in the can is to use a bigger can.’ "

Thats because the vegematic wasnt invented yet. But what i cant figure is, as smart as he was, why would he open a can of warms in the first place?

[:-,]

37

Hello All,

Going [#offtopic] here…

Einsteins’ theory of relativity (E=MC2) was the biggest can of worms he ever opened.

So much so that it took until 1919, almost a decade later, to put all the worms back in this can.

Hope this helps.

38

Funny you should make that association. When I was a student lab assistant in high school my Physics teacher showed be how the differential calculus could be used to derive E=mc2. Now that was putting the worms back into the can I can tell you. I hadn’t yet taken the calculus but I recall being intrigued by the idea that solving simultaneous quadratic equations was way more work than simply using the differential calculus and quadratic solutions didn’t give you “all” the answers in one convenient spot (my maths teacher had previously “allowed” me the pleasure of uncovering the connection between quadratics and geometry all by myself with just some graph paper and my home grown biological computer I carried with me everywhere, in case I needed one.) I studied (Newtonian) physics using only quadratics. Only in the following semester did I learn the calculus. That was frustrating, had I but known the calculus first…