Large Scale Central

Replacement truck bolster failure

This past spring I did a massive 3d resin printing job printing off bolsters and side frames to replace the USAT trucks under my modern equipment. The files I got online and included pre designed holes for 3mm x 6mm roller bearings.

At the time I was dumb and sold off all but a few of my USAT friction bearing trucks because I thought this was the forever replacement.

Then about 3 months later I go to grab a car and the wheels fall out. Inspection of the truck shows the bolster had deformed and flexed under the weight of the car.

So stupid me, prints off a few more and tries again. Same thing a while later. So I say screw it, and run a RTV mold of the few original truck bolsters I have left and cast a bunch in casting resin. Replace all the bolsters…

Then a few months go by and I’m in the same boat…

I’m at a loss so I figured why not put a styrene strap across the bottom to flex it back.
I do that and it seems to help but some of the trucks still are flexing inward. I really wasn’t consistent on the length and the hole where the screws goes through so some pieces might be longer/shorter by 1/16 to 1/32"
All of them have minor deflections a month later but a few have issues like before

Ideas for solutions?

Option 1. Have someone print me ~100 bolsters from a FDM printer
Option 2. Try a different casting resin
Option 3. Try a different 3d printing resin.

Option 4?
Option 5?

Your first option should be changed…
Since USTrains still produce replacement parts; and we all should be supporting this; Other manufacturers often don’t…
How about limiting your new and improved hobby of 3D printing to those parts not available…
A pair of USTrains trucks, without wheels is not all that expensive…be supportive of them, and purchase new ones.

Often I see problems with Bachmann truck bolsters, cracking under stress. The stress in some cases is formed when you cut off the arm used for truck mounted couplers, when converting to body mounts.
First note that the trucks are cast in Styrene, and can be “Welded” with common clear liquid, plastic model “Cement”. Then use readily available styrene sheet, or strips to make re-enforcing strips to weld on at the weak points, while using the same cement to heal the cracks that have occurred.
This sudden craze to use 3D printing as a fix-all, is failing to support the now “Old Fashioned” skill of Modelling, and we all suffer the loss, in the long term.
3D printing is a Hobby on its own, and does have a place in many of the great hobbies available today.
Replacing non-available parts is always helpful, but does not support our “Dwindling” number of manufacturers.

My first thoughts would be a different resin (tougher?) and/or maybe printing with a channel in it for some kind of aluminum angle or C channel?

Well Fred,
I appreciate your reply I’m a bit taken back by the aggressive comment to just buy them. First off, I don’t have the money to replace the friction bearing trucks with a proper 70 ton roller bearing. The USAT trucks have their own set of problems.

And also there is no current company making a roller bearing caboose truck.

If money was no object I’d be buying the Kadee 70 and 100 trucks at $50 a pop.

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I’m going to try reprinting in a tougher/stronger resin. It’s interesting to me that a 4-8 lb rolling stock puts enough weight on the bolsters to deflect like this.

Yea, I’ve had cast resin trucks flex even with no weight on them, just due to the weight of the span of the bolster.

I would suggest purchasing some brass flat bar from Hobby Lobby and add full width strips to the sides of the bolster with a good epoxy. The bolster is taking the weight in the weakest direction of the bolster.

The cost can be dissipated over time replacing as necessary.

If I am seeing this correctly I would suggest some flat stock of metal or alloy across the top of the bolster (material and thickness of your choice…aluminum, brass,steel) . That’s how I would approach it instead of trying to correct the weakness at the bottom. I still see a bow at the top of the bolster ( bottom picture) even with the added “plastic” brace.

Perhaps this helps and perhaps not but the bolster prints you have made are totally workable without seeing the side frames and are the side frames your prints as well?

I see 3D printing as a viable future of garden railroading, being able to make your own cars and trucks an and detail parts and all sorts of things is the way to go. cliff’s Sutro Tunnel dioramas, Craig’s bolsters, BD’s crew quarters building, Dan Gilcrist’s many parts and kits that he works really hard to GIVE away the “plans” and how to.
Craig you will figure it out quickly and hope that the fix is easy and inexpensive . Looking forward to more from you and your layout


The piece with the plastic was post bend. It had already deformed and this was an attempt to bring it back in tension.

Are you suggesting that if the top of the bolster is the Y + axis, then put the cross piece on the X axis? Or put it on the Y- axis?

I think we are on the same page. If the top of the bolster is the X plane, and the vertical sides of the bolster are the Y plane, add the flat bar on the Y plane with the wide dimension of the flat bar in the Y plane.

Take a piece of brass strip and try to bend it across the thin dimension. Then turn it 90° and try to bend it ‘the hard way’. Which do you think will hold up the car better?

And if you make this a practice when making replacement bolsters, they will likely never sag.

Thanks for the idea. The reason I added the styrene on the bottom was an attempt to spread the load more evenly (thinking like how a triangle is stronger than a box). Maybe doing all three might work if your idea doesn’t.

The other thing I was thinking about is a way to mechanically fasten the support with a screw, but I think the cross section is to narrow and the mounting screw is in the way.

I also wonder if I could add the stiffener CAD and print it as a solid unit.

More experimenting needed for sure.

I’m going to ask the 3d print club at school if I can buy some FDM prints as well. I’m pretty sure they have a couple FDM printers.

Try printing in carbon fiber, We have been printing parts for 1/8th scale in carbon fiber with great success. :slight_smile:

Not up to speed with the latest in carbon fiber, but doesn’t that require some post processing? you need a curing oven i think?

We’re using Ellegoo printers (The Big Neptune 3 Max and the Neptune 3 Plus) with SS nozzles, Just print and remove from the plate. Done. We use the Prusa Slicer for the post processor.

Carbon fiber printed. Wow. I would have never guessed that would be possible. Seems like just yesterday carbon fiber was brand new. :joy:

The carbon fiber filament comes in 1 kilo spools (1.75mm) for anywhere from $30 and up.

Interesting but I don’t currently own a FDM printer.