Wednesday, August 5, 2020

CN Woodchip Car - Assessing Limitations

Reality is 3D printing can be a capricious process, and like any tool, you must learn to harness its power and accept its limits. While 3D printing can provide unprecedented opportunities, they come with a cost. This cost is that what you generally take for granted with plastic injection don't always translate well into printing and vice versa. Change the printing orientation and what used to be a fine 3D model can end up a garbled chunk of resin.

Most amateur 3D designers like myself start with a set of theoretical design guidelines relative to a set of specific printer and printing material. It says "minimal depth is 0.1mm" and we take it for granted. Many details will be drawn to be about 0.2 or 0.3 mm, which translate to about 3/4" or 1" in real life. Great isn't it? You can now print almost everything to scale with very little compromise. It is true in some sense and often, you'll get away with a neat printed part albeit a fragile one. But taken in the context of something that must endure the test of time, it is unimpressive. If you add the fact others will want the model, well, they will expect a minimum of quality and sturdiness.

Thicker ladder rungs and redrawn brake wheel and chain
Thicker ladder rungs and redrawn brake wheel and chain

For this reason, I made several compromises, particularly relative to the underframe. I also designed neat brake wheels and trucks. Then we printed them. Some stuff went well, other did not.  Some details printed well, but were extremely brittle. It was a mixed bag and I did expect such results. Then, enter the real life... once again.

A general view of car 879000 new end

Many details need larger cross-section. Some need supports. Trucks had inaccuracies and even if I followed NMRA recommended practices, some adjustment was required. Brake wheels were fine and realistic... but would break the moment you took them of their support. The question remained, how to get a fine scale look with unprototypically thicker cross-section?

Well, it started with an electronic calliper and several plastic freight cars I deemed looking detailed enough to pass my standards. Tichy ladders, Proto 2000 and True Line freight cars, etc. I didn't ventured into Kadee cars... simply because their incredibly small details don't yield good results in resin.

Car 878000 - New ladders, improved brake details

Ladder rungs went from 0.37mm to 0.5mm. Intricate profiles were simplified while retaining some details that could make a difference. I can't say I was happy dumbing down my model has if it was a run-of-the-mill WalthersMainline car, but it had to be done. Stirrups were also significantly thickened. Basically, most small details that didn't print well or weren't sturdy enough were redrawn from scratch.

All that wasn't in vain. While the details are a little bit chunkier than they use to be, the reality it won't be truly noticeable. In fact, I have to ask myself how far I could have gone if I had scratchbuilt the car for a RPM meet. The truth is I couldn't have gone further except with the help of photo-etched brass... Only the underframe could have been better.

Right: original truck, left: improved design

At this point of my journey, both cars 878000 and 879000 have reached a level at which they can be manufactured decently. I also have designed a neat Barber S-2 truck which both look good and runs smoothly as can be. Many compromises have been made since two years ago when I redrawn that project for the first time. Back then, the model would have been cast in resin, provided with plastic trucks and brake wheel, and made use of several photo-etched part. However, change in technology, rise in cost and other factors have made this no longer viable. I'm not that much onboard with 3D printing, but at this point, it is a decent solution that can make this dream come true for me and many others. Maybe it will one day spark the interest of a major manufacturer, who knows.

Meanwhile, another challenge will be securing rights to use the CN logo for the decals. It shouldn't be to hard, but it could be a lengthy process.

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