Monday, September 14, 2020

Keeping Up with Jason: 3D Printing Beet Racks

If you've been following Jason Hill and his Owl Mountain Models, you might see that some of my personal projects have mirrored his commercial projects. He cut molds for his injection-molded F-50-4 flat cars; I 3d-printed the earlier CS-35 flat cars. He's done steam locomotive parts (3d printed and otherwise), I experimented with a 3d printed boiler for a C-11 Pacific. He's experimented with Harriman passenger car customization, and I've 3d printed some C-60-1 bodies.

Some of our overlap isn't surprising. We've got similar interests; we're interested in the steam era on the SP. We're both likely working from the easily-available plans in some of Tony Thompson's SP books (at least until we get curious enough about details to wander up to Sacramento and the California State Railroad Museum library and archives to see the actual blueprints.) We're interested in making lots of particular models - commercially and injection-molded in Jason's case, and for my own use and 3d printed in my case. We've also just been talking lots and comparing parts produced by each other. Many of my conversations with Jason about interesting models and manufacturing encouraged me to try building various models.

The Tony Thompson freight car book on flat cars had more than plans for early SP steel flat cars to inspire us both. He also included photos and plans of the various temporary sides and sugar beet "racks" that the SP used to make the flat cars useful for occasional traffic. Sugar beets were a big commodity on the SP, often seen up into the 1970s going from the fields to the various sugar beet processing plants located in the Bay Area, Salinas Valley, and Central Valley. SP track diagrams from the 1960's even show a track in Mountain View labeled "sugar beet dump" - about where the Microsoft, Google, and LinkedIn shuttle buses pick up folks at the Mountain View station... or at least where they picked up employees in the days before COVID-19.

Sugar beets were heavy, large, and were shipped in huge volume during the harvest season, so the SP needed a cheap and easy way to ship them. The crop was too seasonal to deserve dedicated cars, too bulky for low-sided gondolas, and too low-cost to deserve anything too nice. So during the first half of the 20th century, the SP would build latticed sides out of two-by- lumber that they could put on any ratty flat car, dump the beets in the top, and open the sides to let them pour out at the sugar refinery. When those cars got too worn in the 1950's, the SP took steel gondolas, then added wooden sides to increase the capacity to haul more of the relatively-light sugar beets. The early cars with the latticed sides are much cooler in my opinion than the later cars - the airy, slatty cars always looked a bit jury-rigged, and battered and worn enough to give a modeler lots of weathering fun.

Close-up of beet rack

Jason and I chatted long ago about the beet racks and how they make interesting cars. Since then, Jason took the effort to cut injection molds for his Blackburn patent beet racks, sized to fit his F-50-4 flat cars. They're beautiful models, with much finer detail than I can get with my 3d printer. All those conversations also encouraged me. I went after similar cars a couple years back, 3d printing a few beet racks based on an earlier, non-patent design also in Tony Thompson's book. If you want a few beet racks for your layout, I'd go buy some of Jason's. I'd still like to tell you about mine because they say a bit about what's easy and hard with 3d printing.

Jason's beet racks are separate plastic parts sized to fit his existing flat car models. Injection molding's good for that; it's a reliable process for high numbers of parts, and parts keep the same dimensions. To keep costs low, making parts flat, thin, and consistent thickness makes the molds easier to cut and run, and minimizes warpage of completed parts. For the beet racks, that means that making the slides as four flat pieces is easiest and the most inexpensive. In contrast, large 3d structures are hard to do with injection molding. Trying to print the flat car and the beet racks simultaneously would require large, deep molds with several pieces that need to slide together to close the mold - a challenge for the major hobby manufacturers, and near-impossible for the garage manufacturer.

3d model arrangement in the printer: bodies printing vertically, with rack ends as a separate part.

With 3d printing, the rules about what's hard and easy are completely turned around. Because of printer miscalibrations, a printer might have slightly different scale in different directions, making it hard to keep parts the same size unless they're printed in the same orientation or axis. Printing thin, flexible things can be hard with the Form One because the part will flop during all the movement as each layer is printed. As I've mentioned before, my Form One's temporary support structure relies on many little sprues to hold up the part and form the surface it begins to print from. Where a part starts printing is often roughest because of these supports; the best detail is usually much better in the middle and top of the parts. I like to think of it as "the 3d printer doesn't like to start new parts". If I can print a new layer that's well-connected to the previous layer and requires no outside support, I'll have better quality and more successful prints.

I'd started trying to do the beet racks as separately printed parts, but found that didn't work at all. The resulting parts were floppy, inaccurately sized, and rough where the supports attached. I ended up redoing the model so that the beet rack sides were part of the flat car model, and the ends were separate parts printed on a separate support structure. I also printed the models vertically, again omitting part of one end so that the support structure wouldn't join to a visible face, and then 3d printed a separate part with two feet of deck and the car end. As a result, I only needed supports along a short edge of the beet racks rather than along one of the longer edges. The attachment to the car body also stiffened the lattice structure.

As always, detail that's close to the plane of major parts is easy to apply and comes out fine. The hinges and door latches are just embossed designs raised up or lowered relative to the rest of the design. The slats printed well as long as the board was well supported, and connected back up to posts frequently. Rather than trying to fiddle to get posts and stake pockets to match, the single-piece body made it easy to have everything look realistic and fitting well.

The beet racks also showed how 3d printing works great for variants. For Jason, cutting a new version of a flat car often means designing and cutting new molds from scratch. With 3d printing, it's much easier to borrow the flat car model, combine it with the beet racks, and print a combined model. It also made for an easier model to assemble, without any need to get the beet rack sides and flat car body aligned correctly, or to figure out how to trim posts to make sure the sides matched the stake pocket locations.

The area I model around San Jose, Campbell, and Los Gatos never had sugar beets as far as I know. All the local sugar beets were grown in the flat lands around Moffett Field, rather than further south in the Valley. For example, Henry Mitarai, a Japanese-American farmer, grew acres of sugar beets on his farm off of Mathilda Ave. in Sunnyvale during the 1930's. Dorothea Lange photographed him in his fields in 1942; shortly after, he and his family were sent off to the Heart Mountain internment camp in Wyoming for the duration World War II. Mitarai didn't return to Sunnyvale after the war; he and his family stayed in Utah and grew sugar beets.

Even if the sugar beet cars aren't appropriate for my orchard layout, they're cool cars. They're also a nice reminder of the history of the Santa Clara Valley: we grew many crops besides fruit orchards, our current urban towns had agrarian beginnings, and we made money in some interesting ways before social networks.

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