The Definitive Buckeye Truck

Here is another project in the works:

I'm considering redesigning my DODX flatcar to go along with these new trucks. I found a set of Buckeye truck drawings in a book at the university, so this is a project I have been excited to revisit. The old truck had a slight error in the wheelbase; it was a few inches too long. This new model will fix the trucks, and hopefully I can readdress the flatcars and check their measurements again too.

I want this model to be top-of-the-line. I'm designing the model around the new code 88 Tangent spinning bearing wheelsets. They work similarly to the Athearn Genesis roller bearing design, but when I saw the wheelsets being sold separately on the Tangent website, I knew I needed to use them.

Right now, the sideframes will be rigid. Having the flexible joint in the middle would be cool, but I don't think the trucks would print or operate reliably. I'll probably provide a little play in the center axle to allow the truck to track a bit better.

I'm also considering a sprung version, but again, I'm worried about reliability. Unsprung rigid trucks may allow me to print the truck in one piece, with bolster and sideframes in one. The Tangent axle snaps into the bottom of the journal, no needle points that require spreading the sideframes. My previous trucks used a 3-piece design, where the bolster and sideframe had to be assembled around Kadee or intermountain wheelsets. That was to avoid needing to flex the sideframes and accidentally snap the brittle 3D printing resin.

 

So far so good! If you don't already have the drawing from the Car and Locomotive Cyclopedia as well as the accompanying photo, I can send it to you. I was also drawing this truck at one time, but I didn't have a need for it so since it was just an exercise for me I stopped.

Also, if you weren't already aware, Spring Mills Depot is in the tooling stage on the DODX cars in HO scale:

http://www.springmillsdepot.com/dodxmain.htm

Whether that stops you in your tracks, inspires you to carry on or doesn't affect you at all I thought you might like to know. They have done nice work in the past with their previous factory in China. After the AFFA shakeup a few years ago they had to locate their tooling and find a new manufacturer which they have done. Personally, I'm hoping for another run of the canstock boxcars.

I had a similar revelation the other day about using the Tangent wheels. This would solve a lot of problems for me as well. We both approached printed trucks with the idea of assembling the trucks around the needlepoint axles. The brittle nature and near rigidity of the Frosted Detail material from Shapeways made it a necessity. In fairness to Shapeways, their material and printing methods result in extremely precise parts which allow for ease in designing and assembling interlocking parts. The trucks I printed years ago hold up quite well.

When I've tried interlocking parts with resin printers I'm not having as much success as with Shapeways. Part of the problem is I don't design enough slop in the part, but these trucks don't really tolerate much slop to begin with so it's a chicken or the egg problem. I did have some success with printing the National Uni-Truck II as one piece, but I had to design some triangular prism shaped slots for the needlepoint axles to pass through on their way to the journal, which weakened some details. The journal also required cleaning out with a Reboxx axle tool. There was just enough flex in the resin after the triangular slots were incorporated into the design to allow the 28" wheel to fit. Unfortunately, there are no commercially available 28" wheels with the rotating bearing cap so this truck isn't a candidate for the rotating bearing option.



I think you'll be OK with the rigid truck design. I think the end journals could be like the letter C to allow the axles to clip in and the center axle could be the same but elongated into a slot shape to allow some vertical movement, say 0.035 inches or so. You might also explore the idea of manipulating the width of the center journals a bit to allow side-to-side movement of the center axle, but I'm not sure how much movement is available in the Tangent design.

 

yeah, I'm using the drawing from the Car and Locomotive Cyclopedia. The engineering library on campus has all of the most recent ones, so I have been checking them out and scanning pages for projects I'd like to do in the future. I think this is the same set of drawings Bobby Pitts used for his scratchbuilt version. He posted some photos in an HO thread a while ago.

I like the idea for lateral movement of the center axle. I'll look into that when I work on the center section. My main concern is the roller bearing end cap making contact with the journal. It's just a press-fit piece on the end of the axle, and I'm worried that transferring too much load to it will make them fall off. The Tangent axle has a shoulder on the inboard side the journal surface that prevents too much lateral movement, so I'll try to work with those dimensions. I picked up a Tangent Greenville boxcar the other day, so I have been using calipers to go around and measure the wheelsets and bearing surfaces.

In regards to the Spring Mills DODX car, I think they are my biggest competitor (if they can actually release the model). Their price point is pretty similar to the price that Shapeways charges, but with a four or five year delay on their model, I wonder how many will actually end up in hobby shops. The on-demand nature of the Shapeways business model will hopefully preserve the market for my model, especially for people who don't want to wait for Spring Mills to get their act together.

They are also offering their truck on an individual basis: http://www.springmillsdepot.com/DODXtrucks.htm. My justification for this project is to do something better than they can. Hopefully the functional bearing feature works out, and I also plan to make the bolster more accurate and potentially add brake beams too.

 

There you go! That's what I appreciate about you. The same thing drives me in my design efforts. I'm looking forward to your results.

 

I just remembered I have some photos you might find useful:













When I was poking around to get these photos I was actually looking toward the loading dock and the cars were sort of in my way. I will eventually finish my Free-mo module depicting this industrial lead.... someday.

 

The 'roller bearing' is actually closer to the classic solid bearing on freight cars of old. The wheelset has a machined-down straight axle on the ends, and there is a shoulder on the inside that keep the axle centered between the sideframes. The spinning bearing cap is press-fit onto the end of the narrow axle that rides in the journal. I wish I had some good photos of an HO model, but all my stuff is at home and I'm back at college to wrap up the last few weeks of the semester.

Here is a screenshot from the 3D model though. I highlighted the bearing surface in red; you can see where it clips into the sideframe. The axle is just a stand-in for testing clearances, the real Tangent one is not so angular, especially around the shoulder area. The real one is a bit more tapered or chamfered.


This system has been used on Athearn Genesis models for a while now, Scaletrains uses it on their Rivet Counter freight cars, and now Tangent is doing it too. Kato had an ASF ride-control truck with spinning bearings as well, but I don't think they are in production anymore. You can still find them on eBay or at hobby shops sometimes though.

For a solid-bearing truck with no needle-point axles, they all roll pretty well. I have at least one set of trucks from each manufacturer. I'll have to do some testing, but my train lengths are not super long, so I doubt any additional friction is very apparent. I'm not sure what the long-term wear on these will be, but with many high-end HO models coming equipped with spinning bearings now, the design seems to be successful. The delrin-metal interface has been trusted by modelers for many years on needlepoint bearings, so hopefully the new change in geometry doesn't affect lifespan.

 

I also found a source for 28" rotating-bearing wheelsets: The Scaletrains Gunderson autorack. I'm not sure what the differences in geometry are between Tangent and Scaletrains wheels, but if Scaletrains offers replacement wheelsets, that would be the best place to start for a potential Front Runner redesign.

 

Thanks for finding those! Hopefully that will be an option. I've requested ScaleTrains make their trucks available separately in the past. Might be a good time to ask again and add these wheels to the list. I would like to see the code 88 version, though, since the wheel is so prominent on the Front Runner.

 

Here is a quick update on the truck. I got the outboard sideframe segments finished, I just need to make the small middle section for the center axle. The big update from the previous photo are the casting markings and text molded into the sideframes.

I've been working on the bolster and spring package too, they are coming along pretty well. I'm still unsure how I will screw the truck to the body bolster of the car, and I've been trying to keep it as generic as possible to allow for use under varied models. The big challenge for the center sideframe section will be figuring out how to remove the center axle to maintain access to the screw.

 

That looks fabulous!

If you're going to use the rotating bearing cap axles I think removing them to access the screw is a fair option. Otherwise you could offset the pivot point to one side or another of the axle. I think removing the axle is the best option, especially considering how rarely one would be removing the trucks from the model.

One hedge against breaking the axle clips on the center axle would be to make them slightly more open than the outer axles. This would give a bit of slop to the center axle (yaw movement), but we're only talking a couple thousandths so not anything to interfere with operation. If you can print through another vendor besides Shapeways you'll be able to experiment with more flexible resins. Their acrylic FUD material is just not forgiving at all and none of their other options can execute that detail. I sure do miss their Black High Definition Acrylic material...

 

Here are the center sideframe sections by themselves. I made two versions, which I am calling 'early' and 'late.' The 'early' version is at the bottom, while the 'late' version is on top. I have seen DODX cars with both versions, and it allows for making multiple truck variants for Rail Whale tank cars too. The 'early' version came from my set of drawings, and then I adapted it by eye to match photos of the 'late' version under other cars.


I am considering printing these as separate pieces, and then gluing it to the main sideframe after the wheelset has been assembled. The problem I ran into with a removable center axle is the fact that there is part of the sideframe below the axle. Unlike a regular 2-axle truck, where there is nothing below the journal, the center section completely surrounds the bearing, which prevents the axle from dropping out like I need it to.

The 'early' sideframe has an axle dropout slot as a concession, but the different geometry of the 'late' version would necessitate cutting all the way through the bottom of the sideframe. I am not willing to sacrifice a major detail like that, so assembly is the best thing I can think of.

 

Here is a look at the brake equipment. I modeled the trucks with truck-mounted brake cylinders, but I may do a version with body-mounted cylinders too. I'm not even sure what kind the DODX cars have, now that I think about it. The body-mount version probably wouldn't have the full lever system, just the brake beams on a simplified mounting. I don't have enough information on a three-axle truck body cylinder system, which is roadblock I hit on the first version last year.

I do have one problem with the truck-brake version though. I'm not sure where the piston rods of the unpaired brake beam go. The drawing cuts them off for a section view, so it doesn't show what they connect to. You can see them on my model basically floating in space. This may not be a big deal, as they aren't very visible when the model is on the tracks. The piston rods are separate parts from the brake beam; I added holes to the brake beam so you can use .020" brass wire instead of printing the piston rods.

 

Here are the side frames out of my printer with minimal cleanup. I took them off the supports, but haven’t done any sanding or other cleanup to them. The brake beams need the most cleanup, you can see some residual supports still on them.

I did end up printing the center section as a separate part, and I was surprised how well it snaps in place.



It’s a bit difficult to get my camera to focus up close on such small items, but the details are super crisp. The text is barely visible, I may make it a bit thicker on the file for future prints. One thing I have noticed with this printer is that details are a lot smaller in real life than they appear on the CAD file. Seeing everything with black outlines is one thing, but once they print, things like rivets end up being smaller than they seem.

 

Bravo! That looks really good.

I can relate to the tiny details in the CAD file. I usually draw everything 1:1 then "convert" the model to scale for printing by fattening details here and there. I forgot to modify a door latch on a trailer door and noticed later after printing that it had somehow printed to a scale thickness. Sometimes the capability of these printers can be astounding.