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Since there's a shortage of O scale Helium Cars on the market (we've all seen the old wooden kits and the (VERY) expensive brass ones, and it seems to be the rage at the moment, I figured I'd take a crack at one too, since they'd regularly pass through South Amboy, NJ on their way to Lakehurst NAS.

Now, designing one is simple. Designing one that'll print correctly, be fairly detailed, fairly accurate AND work with the limitations of 3-rail is the trick.

Towards that end, I decided to attempt to make in in 2 main parts, a chassis and a body. I'm using water washable resin to prototype (as it's a heck of a lot easier to clean up), but the final product will be printed in something more durable. Some of the detail will need to be added the old fashioned way (metal parts, by hand) just because it's tons easier to do it the old fashioned way.

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This was a test print of the chassis (shown bottom side up). The shadows are wavy, the chassis isn't. More brake detail will be added to the final one. The grab handles on the ends will be replaced with brass ones, as they just end up too delicate if printed. Getting the brake line to cure in a straight line is proving challenging, its diameter may need to be increased. I've re-printed with added detail in Siraya Tech Blu, but I don't have a picture of it yet.

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Final render showing both pieces together. Yes, that's over 2500 rivets. Don't count them. There were at least 8 different generations of Helium cars, and good pictures are few and far between, and usually don't differentiate as to which version they're of. This is as close as I can get to a model of a 3rd generation car, built between 1942-43. As the period I model is from the mid 40s to the mid 50s, that's what I went with. I'd post a picture of the body printed, but sadly, just prior to the print finishing, the resin ran out. It took over 1L of resin to print the chassis and body (which is a ridiculous amount!)

Of course, you can't just stick it on any old set of trucks (well, you COULD, and it would save me a ton of time, but...). 3rd generation cars rode on Barber ASF solid bearing trucks (probably 100 ton) with clasp brakes. Try finding those at your LHS! So, after trying many different things to get something close to prototypical that'll run on 3 rails, I decided to go with MTH die-cast trucks with custom printed sideframes:

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Once again, try and find decent pics of the prototypes. I'm working off of blurry reprints of 80 year old photos... The brake beams haven't been added yet in this pic (and the modified trucks shown are from another project, stock ones are being delivered). I needed to fit these first so that the brake beam design will attach to each end AND clear the coupler. Fun times! Rather than attempt to accurately print 3 mm thread inside a hole, I've just got 2 mm bolts with nuts on the bottom holding them together. But they actually fit correctly on a piece of track and roll!

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Thin metal stamped truck frame? What is this, 1940? Nobody does that anymore. The resin I'm printing them out of should be able to handle the load. I know the Siraya Tech blu would, but that's overkill for truck sideframes.

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Placement of the clasp brakes is just mocked-up here, as the test piece proved too narrow. Final one will be higher, closer to the wheels, and fit across both sides into holes in the sideframes. Importantly, they clear the coupler!

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And the "darned close to final" 100 ton Barber ASF truck with clasp brakes. Still not the final MTH truck (they won't have pickups), but I'm still waiting for them to come in. I'm probably going to remove the "thumbtack" to provide better clearance, since I don't need it for anything. Have to see where it sits on a non-modified truck.

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With flash, to show the brake details

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And without, to show how it'll normally look.

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So, after many aborted printing attempts, I'm getting closer to something useful. First were issues with the resin. I'm using Elegoo ABS-Like, as I wanted something that can handle some handling without breaking from being brittle. Works fine on the smaller printer (that's what I printed the truck sides in), but when dealing with large prints, I was getting a lot of support failures. Tweaked (and tweaked, and tweaked) the settings, and finally got close to something usable.

The walk on the roof warped all to **** after the supports were removed. Same thing happened along the sides with the bracing. Sadly, anything close to scale thickness just isn't as structurally supportive when printed in resin instead of fashioned from steel. I may be able to get around this by printing the body in smaller pieces, curing them with the supports attached, then assembling it afterwards. I've already modified the model to allow this to happen.

I do have some useful parts. The helium tubes are good, as are the ends (with the exception of the ladders and some of the grab irons).

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Detail on the door ends came out good, ladder will be removed, printed separately, and attached.

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Same thing with the ladders on the brake end. Brake wheel came out good, connections from it will be made with chain and brass rod.

Still more work to do, but progress made!

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Latest work on the prototype. Shown here without the chassis (and without braces on the far side, yet). I've made several changes to the model so that production of subsequent ones will be easier, but I can still get a useful car out of this one. Since the last pic I've removed the walkway, ladders and side braces, printed them separately and put them all together. Quick coat of primer so I can see what needs more work. Screws through the chassis attach the body (once we get to that point). Chain and a brass rod will connect to the brake wheel. Hoping to get it finished this week...

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A few minor tweaks left (grab irons here and there, etc...), but the prototype is pretty much done. For the next one, the body has been split into 6 parts, both for ease and speed of printing, whereas the prototype had several test prints pieced together and parts replaced as the design process went on. Always fun trying to force fit pieces together that weren't meant to be apart in the first place!

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Last edited by Magicland

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