More adventures in 3D printing - Santa Fe tank cars by Tom Madden

Some of you may remember that ATSF Tk-G, -H, -I & -J wasp-waisted company service tank car clinic I presented at Cocoa Beach a few years ago. It used 3D printed cores for the tank and domes, with Avery adhesive label overlays for the circumferential courses and dome wrappers and Archer rivets for surface details. At the following Prototype Rails Richard Hendrickson and I lobbied Frank Angstedt on behalf of the East Coast Santa Fe Modeler's Group to see if InterMountain was interested in producing the cars, and I redid my 3D CAD designs for injection molding. IM wasn't interested, but the redesign let me work out some issues on where to split the tank, how to attach the running boards, and generally make it simple to mold and easy to assemble. In 2012 I updated the clinic and presented it to the East Coast Santa Fe group, but the hardware part of the project remained in limbo until earlier this year. (I was stuck on how best to design the very complex underframe so it could be cast, and I wasn't really happy with the overall "softness" of the look of the Avery/Archer tank shells.) Tank Earlier this year I redesigned the tank parts yet again, for resin casting. Here are design photos of the upper and lower tank shells: The parts were run lying flat (stereolithography again) and, as expected, had lots of stairstepping. Here's a photo of that unsatisfactory upper tank shell:

Then a breakthrough. We activated the "high fidelity slicing" mode on our Viper hi-resolution stereolithography 3D printers. Why we hadn't done so earlier is a long story, but the change gave parts with incredibly smooth side walls. I jumped at the chance to demo (demonstrate, not demolish) my tank shell parts. We ran them standing on end, and the results were spectacular.Here is a photo of the actual upper tank shell. The part was lightly sandblasted to break the gloss, then primed to seal the surfaces. Archer rivets were added, then the part was primed again to seal the Archers. NO OTHER FINISHING WAS NEEDED! No hand sanding, nothing. Everything except the rivets was built as part of the shell. Everything. Here: Here's a shot of both tank sections, with closeups. Note the absence of stairstepping. Getting the Archer rivets in between the longitudinal ribs was easier than I expected:

Underframe With the start of a good tank pattern in hand I decided to design the rest of the parts and have Shapeways fabricate them in their Frosted Ultra Detail material. The center sills were done on our PolyJet machine several years ago, so I designed the underframe around them, as a flat casting. There were three iterations, adding more detail each time. Here are a couple of screen shots of the final one piece underframe design: The triangular webs on the end sill braces are 1/2" (.006") thick. You can't see them unless the car is upside down, but they're pretty neat! The crossbearer halves on the near side have grooves for placing the train line, and the train line holes in the bolster webs are spotted for easy drilling. The upper crossbearer halves are separate pieces. Shapeways did a beautiful job all three times. Everything built - poling pockets, side bearing supports, tank band anchors and all. The parts needed final cleaning in hot water in an ultrasonic cleaner to

remove wax residue, and non-orthogonal surfaces need light hand finishing to remove roughness and eliminate minor stairstepping. Then it was sandblast, prime, Archer rivets (on the faces of the bolsters and within the end sill and side sill channels), and prime again. Here is the result, with the center sills added: Domes Three different domes are required to cover the four classes of cars. Here are screen shots of the design with all three domes and a couple of passenger car parts as one assembly. The Tk-G uses the small dome, the Tk-J, the large dome, and the Tk-H and -I the mid-size dome :

Shapeways charges by the amount of material in the part, thus the gridded support. Here's the actual Shapeways part, and the mid-size dome after Archer rivets were added. (The dome hatch cover was made several years ago by PolyJet at the same time as the center sills): Running boards and all the fiddly bits The prototype running boards were mounted on brackets attached to the tank supports: That arrangement is clearly too flimsy for an HO model, so I came up with a "ladder" design which traps the running boards between the upper and lower tank shells. Here's the design as sent to Shapeways, and a photo of the finished part. The design includes with a whole bunch of small parts attached in the openings. Shapeways charges by the part, and this is all one part. The running board ladder was designed for flat casting so all the detail shown is on the underside:

Assembly The moment of truth.... Here is a photo showing all the major castings. The ends were also done by Shapeways but weren't a challenge. The cleanout plugs at either end of the upper tank are old Kemtron castings: And here's a photo showing everything dry-fitted, including one of Jason Hill's (Owl Mountain Models) beautiful twin safety valve casting:

Comments This is about the creation of the parts by 3D printing, not about the design, and is intended to show what's possible when you stay within the capabilities of whatever 3D printing process(es) you use. I used PolyJet, stereolithography and MultiJet (Shapeways) to make these patterns. Much remains to be done before the castings shown above become production masters. Most of the "fiddly bits" are done but need Archers applied. I'm very pleased with how it's gone so far. Tom Madden 7/19/2013