Live in Bakersfield: 3D-Printing Freight Cars at Home

By the way, if you've been following my stories about 3d-printing the Hart convertible gondolas, flat cars, and those 1902-era Battleship gondolas, note that you'll get a chance to hear about them in person.

I'll be giving a clinic on 3d-printing freight cars at the NMRA Pacific Coast Region's annual convention in Bakersfield this month. If you've been reading the saga so far, you'll be familiar with what I've been up to. However, you're still likely to enjoy the specific stories about what went well and what went badly. I'll also bring many of the models so you can see the 3d printed cars in person.

Jack Burgess is also offering a clinic on Saturday morning with a nuts-and-bolts description of using SketchUp software and Shapeways print-on-demand service to print out detail parts.

The PCR's convention is April 19-23 at the Doubletree in Bakersfield; there's more information about the convention at the PCR web site. My talk will be Friday, April 21 at 2:30.

Hope to see you all there!

Showing off the 3d Models

I’ve obviously been writing lots about the 3d printed freight cars over the last several months. Apart from showing them to the local model railroad lunch group, I’ve had few chances to show them off in person, show off what 3d printing can do, and share models of otherwise unavailable freight cars.

Last weekend, I went off to the Bay Area Prototype Modelers meet. BAPM is a yearly get-together for sharing models and discussing techniques. BAPM is arranged as show-and-tell; they provide tables, you put down models. Unlike NMRA meets, there’s no contests or judging, no explicit demands for lengthy write-ups describing the prototype - just modelers coming together to share what they’ve been doing. BAPM isn’t unique; there are prototype meets like this elsewhere in the U.S., giving modelers a chance to share. The meets also tend to attract folks interested in specific prototypes, and in modern (1980 and later) models. (See BAPM’s photos from the meet, or read Tony Thompson’s review of the event.)

This sounded like a great crowd to see the freight cars - even if my models aren’t perfect, I suspected folks would be interested in using 3d printing for making specific prototypes. So I hauled a bunch of my freight cars off to Richmond, spread the cars out with a bit of information on how they were made, and had some good conversations.

I went in with a bit of an agenda - the same one I’ve shared here often enough. I wanted to show that a home 3d printer (ok, a pricey home 3d printer) could make models that were approaching the quality of injection molded kits. I wanted to highlight that the technology worked really well for making lots of cars, both because printing a new car was easy, and because I’d end up with lots of “good enough” test prints as I was working on my design. I wanted to show that designing the 3d model was tedious, but possible for folks who were novices at making CAD drawings. I wanted to stress the race between having enough models, and finally getting the design with all the detail I want.

Folks heard that message loud and clear. Harry Wong, one of the organizers, walked up early in the day, and asked “which of the cars was 3d printed”? I waved at all twenty cars laid out on the table. “All of them.” (Pro tip: when showing off 3d printed models, always bring a whole bunch of models to stress that you can make these at will.) Tony Thompson, who wrote the SP freight cars books I used for source material, loved seeing SP prototypes that weren’t available commercially.

I also shared how the 3d printer made it easy to make all the little parts for set dressing - lug boxes, drying flats, piles of sacked prunes. Those parts might not be cheaper than the commercial ones, but it’s nice to be able to make new ones whenever I’m in a set dressing mood.

I also broke one of the prime directives of BAPM. In violation of all the “don’t touch the models” signs, I brought a handful of 3d printed parts for people to touch and examine so folks could get a real feel for 3d printing. (I explicitly had an area on my display to hold the “ok to touch models”, and marked them all so it was obvious what was touchable.) A couple folks noticed the slight warp I’ll get in some of the flat cars (sometimes fixable with careful drying in the sun, sometimes not). Others could feel that the 3d printed cars could be robust enough for operations, or get a sense for the level of details on the models.

Several others asked about what it took to make a 3d model, and whether their particular model could be printed easily, either at Shapeways or on the Form One. One modeler scratchbuilding wind turbine blade loads for flatcars asked about 3d printing some of the odd-shaped mounting hardware that the real railroads use to hold the windmill blades. His particular pieces were perfect for 3d printing - small, slightly odd shapes, with enough bolts and other details to make for an interesting model. Some folks were asking about boxcars; I mentioned my one try at a boxcar and that the 3d printer didn’t do perfectly flat surfaces as well as styrene sheet.

Meanwhile, I also got to see some great models. Along with lots of traditional modeling, I saw three or four other folks building with Shapeways. Jason Hill of Owl Mountain Models had a Shapeways master for the Southern Pacific F-50-4 flat car he intends to make as an injection molded kit. (I spent a good ten minutes comparing my model and his to see what detail I left off; Jason's crawled all over the similar Union Pacific flat car at the Orange Empire Railroad Museum, so he's matched the prototype much better than me.) Other folks were using Shapeways to make specific boxcar doors that weren’t available on production models. There were also a ton of great, traditional models; Jesus Pena showed off the huge fleet of UPS trailers he’s been building for his Free-mo Richmond intermodal yard - at least forty trailers, with plans to double that number for realism.

BAPM is definitely a great meet, and worth attending; it also got me fired up to do the next set of refinements on my models. Next year, BAPM will again be in Richmond on Saturday, June 18, 2016. I’m hoping I’ll have some new models to show off there!

Printing a Freight Car: Southern Pacific CS-35A Flat Car

I’ll admit it. I’m not a freight car modeler. Sure, I’ve had an appreciation for appropriate freight cars from my era, and I’ve built a lot of resin kits for the Vasona Branch. But I’m not one of those folks who could argue the difference between the different patent pressed-car ends, or could tell you what percentage of B-50-14 boxcars had Bosendorfer side doors, or would argue about the appropriate underframe for a stock car. But, hey, all that goes out the door when I decide to print freight cars on the 3d printer.

My list of potential 3d-printer projects has always included a few freight cars. As popular as the Southern Pacific may be, modeling the 1930’s means building a lot of resin kits, searching eBay for old kits, or finding a lot of stand-ins. One example would be the Hart convertible gondolas, frequently used for dumping ballast on railroad tracks. Another would be flat cars - Southern Pacific’s 1930-era flat cars look much more fragile than the typical 1950’s plastic flat car kit that’s available, and tended to have a very specific look. More importantly, I needed flat cars for the Vasona Branch - lumber coming from the sawmill at Laurel needed to come down the hill to the lumberyard at Auzerais St.

I’d hoped my first-generation Makerbot was going to help me with freight cars, but it couldn’t print something that looked good at HO scale - the layers in the plastic were too obvious. The Makerbot could only print within a 4 inch cube - not big enough for even a smaller flatcar. The Form One, though, was getting big enough. At 125 mm x 125 mm x 165 mm, the printer could print a 36 foot freight car diagonally, or a longer car if I tilted it up on end. So, soon after I’d gotten the Form One up and printing, I tried a couple flat cars. Here’s the details on that first flat car.

The Prototype: Southern Pacific CS-35A Flat Car

In 1903, the Southern Pacific decided to experiment with freight cars built completely of steel. Two plans appeared that year: the CS-35 car (36 feet long with 40 ton capacity) and the CS-35A car (40 feet long, 40 tons). Both these CS (Common Standard) cars represented first attempts at a flat car with a steel under frame: a pair of 15 inch I-beams along the center, and pressed steel sides tied together by a 19 inch deep C-channel. The two designs were apparently in a bake-off; both designs date from October 1903, but only the CS-35A got the green light. SP had 1,000 of the 40 foot cars built by the Pressed Steel Car Co. in Chicago.

The CS-35A, designed during the Harriman era, differed from later flatcars such as the F-50-2 by having only nine stake pockets on each side compared to eleven or twelve on later cars. Other spotting features was the lack of rivets on the bottom edge (unnecessary in the stamped forms of the early cars, but needed in the fabricated side frames of later cars) and twelve rivets on the side at each truck bolster.

These flat cars definitely looked different from the other standard SP freight cars - relatively shallow sides, no truss rods, and longer than most of SP’s flat cars. Compared with modern freight cars, they look positively wispy and fragile. They also lasted a long time, with Tony Thompson’s SP Freight Cars book showing the cars still in common use in the 1920’s, both for revenue service and for maintenance.

Of course, there’s no models of the CS-35A available, whether as a resin kit or plastic model, so it was a great first try for 3d printing.

The Model

The first question was how to build the model - do I try to print the whole freight car in a single piece? I’d seen models on Shapeways where only the metal parts were 3d printed; the wooden deck for the flat car was done with laser cut wood. That seemed great; the wood deck would be more realistic, and I could print the model upside down on the build platform. (That didn’t work; more later.) I tried doing a couple models where only the frame of the flat car was printed, with big openings below. That didn’t work - the printed piece ended up being too thin to print, and wasn’t strong enough to survive removal. I ended up building the model so the top was solid and 6mm thick; the wood deck would be glued onto that surface.

I did the initial drawing for the CS-35 in SketchUp. I started out sketching the rough shape, extruded it as a 6 scale inch thick slab, then started adding details - first the frame and ends, then more and more detail. I scaled the sides so they were 6 inches thick and printed more reliably. For details - stake pockets and patterns of rivets - I often drew the objects in a separate SketchUp model, then made the object into a group and pasted copies into the final model. I learned that 1” diameter cylinders, 1 inch high, made great rivets. I also marked the holes for grab irons by drawing a 1.5 inch diameter hole.

There were also details I didn’t model. I didn’t add brake gear to my initial model. I planned on using wire grab irons, and grabbed brake wheels from my scrap box. I did need to model the brake cylinder for the car; it’s obvious on all the real photos I’ve seen. I started using the Tichy Train Group’s K Brake kit, and bought a half dozen at my local model railroad shop, but found I was only using the brake cylinder. I ended up building a 3d model for the brake cylinder, and printing the brake cylinder myself.

One of my other surprises when building this was the question of what exactly to build. Any model has compromises - I might not want to add all details, or I might need to change a dimension, or I might tweak the model to fit a model railroad coupler. Figuring out these differences between the model and the real thing is the hard part of making a model, whether by hand, with a 3d printer, or when designing an injection-molded kit. For the CS-35A, I had to decide whether to add some of the underbody beams and braces (no), or what detail to add to the ends (minimal.) I also had to choose between scale dimensions and a reliably-printing model. I ended up making the center I-beam much thicker than in real life so it would print more reliably. Instead of 1 inch, I made all the walls 2 inches thick. I also drew it with slopes inside the I so there wasn’t a difficult transition from thin to full-width.

Flat car and support structure. Support structure holds car at 30 degree angle to avoid any horizontal slice through the middle being too large.

I also had hiccups. I had problems printing the final model because of extra hidden faces; I used Netfabb Basic to clean up the models and prepare them for printing. Even that didn’t work reliably. Because of the Form One’s resolution, making a “watertight” model (no holes or gaps between faces) was critical. On the Makerbot, the low resolution meant holes would usually be ignored when breaking the model into layers. With the tinier resolution, even a small hole could convince the Form One software that you intended the model to actually be hollow. I also found that pieces thinner than 2 scale inches (0.020 inches, or 0.5mm) didn’t print reliably. (The design rules from Shapeways for their frosted ultra detail material have similar limitations.) I found I couldn’t print the freight cars flat on the build surface either without layers failing to bond. Formlabs, the maker of the printer, suggests that large flat prints be done at an angle so that any individual printing layer doesn’t cover a large area. Doing so gave me more reliable printing, but doubled print time. I also found I needed to be careful about cleaning the model - I’d been leaving the finished prints in direct sun to cure, but had problems with warping. Keeping time in the sun short, and making sure both sides were exposed to the sun helped limit warping.

Initial model. Note messed up corner caused by deformation when printing near edge. The other cars weren't this bad, but all cars printed with the long edge tipped had a bit of deformation.

The overall process for printing the flat cars was something like this. First, I’d print a couple models over a day or two. Like all the 3d models, I’d pull them out of the printers, remove them from the build platform, and soak them in isopropyl alcohol to wash away the extra resin. I’d remove the support structure added to print the model, then leave the models in the sun for 10-20 minutes on a side. Another day, I’d spray paint the models (Scalecoat boxcar red in a spray can). I’d drill out holes for the screws holding on the trucks and couplers, then attach both with plastic screws, and cut the screws off flush with the top surface. I’d then add a wood deck using individual 2x8 wood boards stained with india ink and alcohol, gluing them on with contact cement. I decaled the cars, then then drilled holes for wires representing grab irons and superglue them in place and touched up the paint on the grab irons. A final spray of Dullcote sealed the decals onto the model.

I made a couple embarrassing mistakes with the model. On my first try, I used the plans in Tony Thompson’s “Southern Pacific Freight Cars” book to build the CS-35 36 foot car. That model turned out well (and the 3d model is available on Thingiverse). When I went to decal the model, I looked for the car numbers for the 36 foot cars… and realized there were none listed - SP never built any. I'd been printing the Loch Ness Monster of SP flatcars.

To correct my mistake, I stretched the design out to make a 40 foot car. In SketchUp, this wasn't too challenging; I'd select the portions of the flat car from the bolster out, then use the move tool to drag these out the appropriate distance. After I printed a few of the longer cars, I compared them against photos, and realized the model didn’t look right - the wheels were set closer to the center of the cars. The CS-35A looked a bit like the ends of the cars were unsupported. I went back to SketchUp, and moved the truck bolsters in.

The final model requires about 15 cubic centimeters of resin and prints in three and a half hours. The resin cost about 15 cents a cubic centimeter, and about half gets lost during printing and cleaning, so we’re talking about $3 in resin per freight car. Compared to Shapeways, which would charge around $30 for a similar part, it’s not a bad deal. On the other hand, I went through a lot of prints for testing - probably 10 to 12 pieces. Once I got the design and printing settings done, it was easy to print more flat car castings on demand.

I still have some minor problems with warping, and the arrangement of the model usually causes one corner to be bent in a bit. Both they’re still fine models,and I’ll be able to make some reasonable 1930’s flat cars for my layout quickly. One potentially big problem is that the models are very light - only about 1.5 ounces with trucks and couplers, much lighter than the recommended 3.5 ounces. I’m planning to either add weight to the loads on the flatcars, or add some lead sheeting in parts of the model.

The Decals I printed and decaled one of the “wrong truck spacing” cars using a mix of leftover details; that process was amazingly painful. I tried finding some commercial decals that had the needed freight car numbers and tiny lettering, but didn’t find any good sheets at my hobby shop. I ended up deciding that custom decals might be reasonable, especially if I was going to build ten cars.

I drew up the artwork in Intaglio (a vector drawing program like Adobe Illustrator). I tried using Ben Coifman’s Railroad Roman font which I’d bought years ago, but its lettering looked a bit thinner than the stock SP lettering style. I ended up doing half the sheet using the Baskerville font available on the Mac which resembled the SP lettering, but had thicker letters. The bolder glyphs should make it easier to read the cars in my dark garage.

I sent the decals off to Rail Graphics; my 1 inch by 4 inch decal sheet cost $50 for a run of 50 decals, each with enough lettering to cover a few cars. The finest 2 inch tall lettering isn’t legible, but all the other lettering was readable and fine for my cars.

I’d never seen any hints on making custom decals, but designing my first sheet gave me a few lessons. First and most important, I made sure that the car numbers included a bunch of optional numbers that matched the real cars. For my CS-35A cars, car numbers would have been between 78500 and 79499. I added several numbers starting with 78/79, and also made sure that numbers starting with 48, 49, and 40 existed in case I wanted to do some of the other SP flat cars. I added several different car lengths and weight capacities so I could do some of the alternates. I also added the SPMW lettering in case I wanted to model any of the maintenance of way cars seen in photos.

I didn’t think about the difficulty of cutting the decal apart. The lettering on these decals was remarkably tiny; I had to borrow my wife’s Optivisor to be able to cut them apart. I put the “feature” lettering - “dirt collector”, “metal brake beam”, etc. on a single line, so it was easy to cut a strip out, then break out the individual words. For the other lettering such as the reweigh information, I did a lot of cutting out individual words. I wish I’d put most of the data for a single kind of car on a single line so I could cut that line off the decal sheet, then cut the individual pieces off separately.

Oh, and if you decal one car by hand before doing the custom decals, don’t use that number on the decal sheet.

The Final Models

So far, I’ve built six of these cars - two of the non-existent 36’ CS-35 cars, one of the CS-35A cars with the wrong truck spacing, and three of the 40’ CS-35A cars with the correct truck spacing. I also have one model that I had printed by Shapeways in Frosted Detail (the lower-quality.) They’re fine cars for my layout. They look positively fragile next to the chunkier Athearn 40 foot flat cars, and I also know that they’re historically accurate.

What’s next? I also like the look of the SP F-50-4 cars, with their narrow sides but prominent center beam. I’ll show more of my progress on those later. I’m also seeing about building models of the W-50-3 Hart convertible gondolas used in ballast service. Keep your fingers crossed that I can print those reliably.

And finally, let's check out the cars in action:

A Most Excellent Detail Casting

I'm still working towards that article on the 3d-printed flat cars. I've printed a bunch of the flat cars over the last month, and currently have seven on the layout. There's a couple of the "extremely rare" and in fact never-built CS-35 36' flat cars, a couple of 40' cars that I built from a stretched model. As I was decaling one, I realized I'd messed up the truck spacing; the true 40' cars set the wheels closer to the center than I'd modeled. After another tweak to the design, I've got two with the correct truck spacing too.

The printed models aren't necessarily a big win over buying commercial cars, nor are they museum-quality; I'm not looking for perfection, just some recognizable models that I can't get elsewhere. Each one of the flat cars requires some finishing and painting. Then the wood deck needs to be stained and glued on, details like the grab irons and brake wheels need to be added. Finally, the cars need to be decaled.

Today's story, though, is about the detailing part. I haven't been putting elaborate brake detail on these cars, but the old-fashioned K-style brake cylinder is a pretty visible detail and worth adding. I had been buying the Tichy plastic brake gear detail kits, but (1) I kept buying out the Train Shop's stock, and (2) at some point paying $3 to grab one little casting seemed wasteful, especially if I want a bunch of cars.

Hey, wait, don't I have a 3d printer?

So, I tried it - took some guesses at measurements, drew something up over a couple hours in SketchUp, and printed it. And it worked - the Form One did a most excellent job on a tiny brake cylinder.

So I upped the detail, adding bolt heads and even the very fine piston rod and clevis. I printed all these at the 0.025" setting on the Form One. A few hours later, I had a dozen brake cylinders, ready for the next set of cars. The photos are worth sharing; if I ever had any doubts about whether the Form One would help me in modeling, this particular piece convinced me. Zoom in to see that the clevis fork printed (though only half printed fully), and notice the bolt detail both around the top of the cylinder, and on the mounting plate at the back of the model.

As a modeler that buys a fair number of detail parts, these brake cylinders completely change the game - I'm no longer dependent on what's available from the store or what's in stock, but instead on what I can manage to draw in a 3d program.

For the folks who are curious how I drew the brake cylinder:

The first step was to get some rough measurements off one of the commercial parts and off official drawings. Once I had rough shapes, I drew a 2d cross-section of the piece's shape, and drew a circle the size of the cylinder bottom in SketchUp. Once I had these, SketchUp's "Follow Me" tool allowed me to drag that cross section around the circle, making what the high school geometry teachers might call a surface of rotation. That gave me the rough 3d object; I extruded 1" diameter, 1" tall cylinders wherever I wanted bolts. The clevis fork was similarly extruding a circle from the cylinder top, then sketching the rectangular shapes on top of that to make the clevis.

The hardest part was the mounting plate on the top of the cylinder. I did this by drawing a 10x16" x 2" thick block, and moving it so it sat on top of the cylinder. Now, this doesn't work so hot because SketchUp doesn't like figuring out the intersections between curved and flat surfaces, so it just leaves the top half of the cylinder inside the block. To make a 3d-printable shape, I deleted the top face of the mounting plate and drew extra edges at the intersection between the round and square faces, then deleted the parts of the cylinder that were stuck inside the plate.

That's pretty sweet work on a part that's less than 3/4" long, and only around 1/8" in diameter. And that part is starting to get to injection molded quality. Tichy's part is a little finer,includes the Westinghouse logo and cylinder size cast right on the side, and its ABS probably can take a bit more abuse than the Form Labs resin. On the negative side, when I look at the commercial part with a magnifying glass (and I'm using that magnifying glass a lot these days), it's easy to see that the mold was misaligned, and the two halves of the part didn't match up.

Sneak Preview #1: The Rejects

One of the unspoken parts of 3d printing is that you're pretty much testing out a production line. You need to figure out the best orientation for printing the object, do test shots, and iterate.

For example, do I need a support structure to hold the print up while printing? For my first attempts at the CS-35A flat car, I tried printing the top of the car directly on the build platform. Prints on the Form One grow layer-by-layer starting from the surface of the build platform, so I'd get a nice flat surface. I'd save resin because I wasn't spending it printing a support structure to hold the piece off the platform. I'd also have a lot less cleanup.

It didn't work - for whatever reason, the thinner areas just above the table don't always print reliably. You can see it in this pile of rejected pieces, with rotted-out holes showing where the resin didn't harden.

And that's a real CS-35A, 40 feet long just below it. More about that later.

Sneak Preview: 3d Printed Flat Car

Here's a preview for a future article: a 3d-printed Southern Pacific CS-35 flat car, circa 1903. I printed this on the Form One resin printer. The deck of flat car is individual pieces of stripwood, stained with india ink.

My obvious mistakes:

• wrong number of stake pockets (should be 8 per side, not 9).
• set of 12 rivets over trucks should be 6.
• Deck is too narrow - the wood should stick out a few inches beyond the frame.
• The CS-35 was made of fabricated steel components, and should have a hard edge on the bottom edges of the side. The curves are appropriate for the CS-35A, which used pressed steel components.
• The car never really existed, it seems.

That last point was the killer. Tony Thompson's Freight Cars book shows two sets of plans for the CS-35 and CS-35A; only after I built it did I notice that niggling detail that there was no other mention of the CS-35 in the book. The 36' CS-35 was never built; instead, the SP went with the similar 40' CS-35A. Making a design for the CS-35A involved selecting each end of the car in SketchUp, and dragging it out to the proper length.

It's also been a pain to figure out how to print these reliably - to fit on the build platform, each is printed while leaning 20 degrees to the side. But I've now got castings for both the 36 and 40 foot cars. Once I've added a bit more detail on the underside, I can print enough freight cars to keep the Santa Clara Valley Mill and Lumber mill on San Carlos Street busy.