For my 3D printed projects, I need S-2 Barber trucks... a lot of them. To the point it would be hard and costly to source them. About 2 years ago, I designed one in HO scale to 3D print and now the project has reached fruition.
Vitruvius, the famous Roman architect how collected in a series of books the best practices of Antiquity's architecture synthetized every design approach to three basic principles: Firmitas, Utilitas and Venustas. In the minds of the Ancients, any object failing to reach a balance between these fundamentals was considered subpar. In modern language, we would translate these principles as Solidity (robustness, durability, etc.), Functionality (usefulness, practicality, ergonomy, etc.) and Beauty (aesthetics, harmony, etc.). Thousands of years later, these evident truths hold true and I challenge you to visit any ancient culture around the globe. You'll find them applied to a myriad of objects and buildings. In my eyes, it is the greatest lesson for any person dabbling into "building stuff". Among all the modern claptrap and buzzwords our modern world love to bath itself in to give us the impression were are so "different" and "freed" from millenia of human history, they are still consciously and unconsciously applied to judge any built (virtual or real) things around us. Isn't it ironic that cultures known for their love of flourishes in their own designs would still be able to streamline a complex thought process to just three poetic words?
So, with the history lesson behind us, how does this apply to a S-2 Barber truck?
Firmitas: these trucks must be sturdy and a limitation of 3D printing is the use of resin which is, by nature, brittle. Not good for a truck that must be pried open to insert wheelsets and which takes a lot of abuse during running sessions. I could only play with two parameters: finding a decent resin that isn't brittle and designing the part to be able to sustain use and abuse. I addressed the last issue by making the sideframes thickness than what you generally see on plastic trucks. I got the idea from trucks manufactured by Rapido. It prompted me to look at prototype drawings and it became quite evident I could make them thick enough to be stronger (and look better). A mistake I made though was to make the bolster fancy and full of voids to save on resin. Unfortunately, it made the truck prone to break at the junction with the sideframe which was an important failure. Finally, I settled on a solid rectangular bolster... keep it simple!
|Bottom: original design, Top: new simpler design|
Resin was another problem. After experimenting failure with trucks printed by a friend with Elegoo Maroom resin, I was encouraged by Dave Bedard to try my hand at Siraya Tech Fast Grey resin which is far less brittle. I got good results, but after a while, I thought printing black trucks would make painting easier later and if I ever sold the gondola kit, people wouldn't have to paint trucks. The only black resin I could get my hand on was Elegoo, which was brittle... Fortunately, I discovered Siraya Tech offered a clear resin called Tenacious. Having printed parts with this resin, I can assure you can bend it quite a lot without failure. However, I find it isn't the best thing in town when it's time to print high quality details. However, the good thing is that you can mix Tenacious into regular resin to improve them. Most people recommend about adding 20% of Tenacious to a given volume of regular resin. And it works well. Certainly, it doesn't make the Elegoo resin bend that much, but it is far less brittle and print beautifully. I found out it was as strong as my custom mix of Siraya Fast Grey + 20% Tenacious, meaning that it was a well-balanced mix.
Utilitas: The trucks have to be free rolling, easy to print/clean and be NMRA compliant as much as possible. Free rolling was achived by following NMRA standards then scaling parts at 101% to take into account resin shrinkage during curing. It may sound strange, but 3D printing with hobby grade printer isn't magically precise. Discrepancies happen and are normal. You must often tweak perfectly scaled dimensions to take into account shrinking. As for ease of print and cleaning, I had to find the right printing orientation and supports to make it be possible. I won't list everything I did, but let's just say it took several weeks to find something I was comfortable with. Honestly, I'll all good
|Details did matter and had to print well|
Venustas: Trucks had to be as close as prototype as possible. It meant, having the cast lettering of the sideframes and perfectly printed roller bearing details. All these things were easy to model in 3D, but required a lot of experiment to make them print neatly. Add supports in the wrong place and kiss goodbye your details... Another major aesthetic point was the resin color. I once painted grey trucks in black and weathered them only to find out later the paint started to rub off with handling, making them unrealistic and ugly. If a truck is already black, if the weathering wear off, it is less noticeable. Also, I have to take into account many modellers aren't into weathering. Offering black trucks is much more versatile and make assembly and painting much straight forward. As you remember, I recently commented on how designing something for others greatly reduce your level of tolerance to unacceptable compromises.
At this point, I think you can get a grasp that dealing with the 3 principles of design can't be done in silo. They all inform each other and each decision is a compromise between two or even three of them. The result is never "perfect", but need to be a harmonious sum of all parts involved, which Ancient Greeks used to call Symmetria... a much more complex idea than the modern "Symmetria" means nowadays (which is basically dumbed down to mirror effect).