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.
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.
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:
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!