Saturday, May 3, 2014

First Prints: Guggenhime Freight Door

The big advantage of having a 3d printer handy? Quick iteration.

If I need to be perfectly honest, the main job for the new printer was printing out some unusual freight doors for a model I was building. Here are some of the Guggenhime and Company packing house freight doors, 3d printed and temporarily glued on my J.S. Roberts packing house model.

Model with new printed freight door

Original door, Guggenhime packing house, San Jose

Over the last week, I've already done three tweaks of the 3d model for the door. I figured out Tuesday that the model had areas that were too thin to print, and so thickened the base, the handle, and the brackets which hung the door from the tracks. I also found the door was too small for openings I'd cut in the model, so I lengthened the door to ten feet tall. Wednesday's part kept having the track break off during removal, so I added a support piece to protect it. (The doors in the picture are Thursday night's prints.) Friday night, I added a door stop to the left side, added a weather strip above the track to match the photos. (Friday night's prints aren't painted or photographed yet, just wait.)

The real Guggenhime packing house also had two doors, each sliding open in a different direction. With the 3d model, it was trivial to flip one print to make a mirror image. I'd also be able to print some O (1/48) scale doors by scaling up my HO (1/87) model if I wanted to build some larger models.

All these tweaks over three days compared to a month and two rounds with Shapeways telling me, quite correctly, that my original model was too thin to print reliably. Getting told that by a web page that a print won't work is one thing; seeing the warped or incompletely printed details makes the lesson more convincing.

[Photo of Guggenhime & Company freight door from John C. Gordon collection at San Jose State University.]

Thursday, May 1, 2014

First Experiences: Form 1 Resin Printer

I’ve been looking for a printer to help with small model railroad details for a long time. When I'd bought Makerbot's first 3d printer, the Cupcake, back in 2010, I'd hoped it would be useful for making parts and details for my model railroad. My early cupcake was still too coarse and tempramental. I've also sent parts away to Shapeways for printing in their Frosted Ultra Detail. Those parts came out beautifully, but waiting multiple weeks to see whether a design worked is annoying.

My new 3d printer, a Form Labs "Form 1", is a lot closer to what I've wanted for model-making. It has between 3 and 10 times the resolution of the filament-based printers and starts getting close to injection-molded detail. It's got drawbacks: even small parts take a long time to print, designing detailed 3d models requires a new set of skills, and its print material is expensive and easy to mess up. But I think I've found a 3d printer that will be more useful for HO scale modeling.

The Form 1

The Form 1 is a resin-based 3d printer. It uses a photo-sensitive resin to make the parts, shining a laser on the part to harden new material as the partial object is pulled upside down out of the resin bath. Each layer on the Form 1 can be 0.1mm, 0.05 mm, or 0.25 mm thick (.004 in, 0.002 in, 0.001 in). Layers are visible to eye in final object, but are small enough so they can't be felt on the final model. Unlike the ABS extruder printers (Makerbot, etc), layers are made optically, so the Form 1's prints don't have the characteristic ridging caused by plastic squeezing out under the heated nozzle. Layers are anywhere from 3-10x smaller on the Form 1 than the ABS extruder printers.

The experience is completely different. The Makerbot Cupcake was a wonderful DIY project made from laser-cut plywood, but the nice wooden box made the printer particularly noisy, resonating as the stepper motors moved the object and print head.

Form 1 printer. Mine isn't in as clean a setting.

The Form 1, by contrast, feels like a solid professional tool with a very cool modern look. It has an aluminum case with a orange plexiglass box covering the print area and protecting the resin from stray night. The printer has a single button for control and a large display showing the name of the print, time left, and layers to do - information that was on the computer on the early Cupcake. The Form 1 is also quiet, with the only real sound coming from the stepper motors peeling the layer, and even that is quiet. Unlike the Cupcake, I can imagine working in the same room with the printer. (To be fair, the Form 1 is also four times the price of my original DIY Cupcake, and comparable in price to Makerbot's latest professional printers.)

The Form 1 does have its own temperamental nature; I suspect it needs to be in a darker room to avoid curing unused resin in the printer. The potential for spills of resin definitely makes me banish it to the garage. The resin, gloves, and alcohol make for a slightly messier workspace; I'm waiting for some resin spills on the laptop driving it.

The software is pretty simple with few settings: load models, change orientation, add supports for delicate or overhung parts, and print. The computer model of the object downloads completely to the printer upon printing so that computer can be disconnected within a few minutes. I don't have to worry about whether the computer will run out of battery power or fall asleep halfway through a print run and mess up the print. I also can start working immediately on setting up the next model.

Post-processing is more work. Prints need to be pried off the build plate, agitated in alcohol 2 minutes, and soaked in alcohol for another 10 minutes. The resulting parts feel gummy and rubbery at first, but start feeling more like plastic after a day. Support structures can be annoying to cut off.

Design Guidelines

One of the unspoken weaknesses of 3d printers is that the 3d models often need to be redone for each kind of printer. The ABS extruder printers like my older Makerbot might not have been good at fine detail, but could make solid objects efficiently. Large internal areas would be crosshatched to provide adequate support, save plastic and print time. For best results, models needed to be designed for multiples of the extruded plastic width so details could be added with a single line from the nozzle.

The Form 1 has similar design rules that need to be followed. Resin printers aren't as efficient for large, solid objects; the resin is expensive and solid fills are slow. Hollowing models out with 3d software saves money and time.

Freight door model printed on Form 1. It took a few tries, but check out those supports holding the door to the track!

There's also the question of what detail can be shown. The Form 1 prints detailed enough that I need a magnifying glass to look at the detail, but I still found myself trying to get smaller detail than even it could print. On my sample prints, I was able to get detail down to 1 HO inch (0.015 inch) with few problems, but haven't gotten it to print sub-inch bolt and screw detail. The freight door pictured is 10 feet x 8 feet HO, not including the track extension. The track hanging the door is one inch wide, and its long length seems to have some problems printing straight and complete. Bridging empty space is a challenge; the original door handle and track hangars on the freight door wouldn't print correctly until I made them a bit thicker. Again, I needed the magnifying glass to check out the detail.

Seth Neumann's lights, printed on Form 1 with supports. Cutting the part off was not fun.

For pieces with overhangs, the PreForm software can automatically build a model with supports. The supports and "raft" that sticks to the build platform can be bulky - around 15 cc for some of the parts, which is much larger than many of the parts I'm building. Using supports also means that the part needs to be carefully cut from the supports. It might be easier in some cases to redesign the part to reduce the need for supports.

Parts that printed well at Shapeways might not do as well with the PreForm supports. For example, my friend Seth needed 1990's era industrial lighting for warehouses on his model railroad. He's made a compact sprue of parts that prints well at Shapeways. However, the multiple layers of parts (diffusers and small lights) cause problems for the supports. Printing the part flat also means lots of support nubs to file off when preparing the part.

One solution to the support problem is to print objects straight on the build platform, which can work for parts with large flat surfaces and without overhangs. I've been printing most of my parts this way because many are already flat pieces. Printing on the bare platform works for smaller pieces like the freight door. I've heard concerns about warping from the extra laser light to secure the first bits of resin to the build platform, but the baggage doors were doing reasonably well. Building without support structures does mean that you can't have detail on the "wrong" side.

Operating costs

So how much are all those nice parts costing me? The Form Labs resin costs $150 for a liter bottle, or around 15c/cc. For the small parts, a non-trivial amount of resin ends up washed off the model or disappears in cleanup, so perhaps double that price. Machine time is the bigger factor for expensive equipment. Models appear to take about 30 minutes to get initial layers done (one minute per layer), with subsequent layers going much faster (sometimes seconds between peels.) Models with rafts take lots more time and space - a simple raft for Seth’s modern lights model took 20cc of plastic for a 3 cc piece, but the piece did print pretty flawlessly. At $3000/machine, and assuming I get 1000 hours of use out of the machine, that’s $3/hour to run the machine for a 3-4cc piece. Overall, that means that the Form is somewhat cheaper than Shapeways ($5.00 for setup and $2.39 per cc for frosted ultra detail), but not by a significant amount. I suspect I'd still use Shapeways for printing lots of parts when I'm pretty sure the parts will print well, and where I can wait a couple weeks for the part to arrive. The Form 1 will be much better for testing potential designs, for making masters for other ways of making parts (resin casting, perhaps), or when I want a part tomorrow.

Comparing The Form 1 Against Shapeways Frosted Ultra Detail

I've used Shapeways, a 3d printing service, to print parts for my model railroad. Shapeways's frosted ultra detail material is a perfect product for model railroad parts, showing lots of detail and being solid enough to use in real models. Their behind-the-scenes video suggests they're using a 3D Systems ProJet 3500-HD printer, which is a $90,000 machine. Like the Form 1, the ProJet hardens a resin with a bright light to make the model; unlike the Form 1, the ProJet prints the resin with an inkjet-like head, and shines a light over the part to harden it. It also has a nice feature of also printing out wax to support overhanging portions of the parts. The wax support makes the ProJet better for multiple layers of parts or parts with significant overhangs.

Shapeways part on left, first try at part from Form 1 on right. Warping and thinness is my fault; just notice that detail is close.

Here's an direct comparison of a first attempt at printing my Victorian stick-style details against the part at Shapeways. I printed this part badly; I should have made it a bit thicker to help it stand up to being printed from the build platform, but it's still possible to see the detail is comparable. The Shapeways part with frosted ultra detail is a better part without any of the needed cleanup work, but it did have a multi-week turnaround. Having a printer handy when trying to design a part like this is really great, especially as you’re getting acquainted with the material and its limits. The freight door I showed earlier went through multiple revisions that kept getting rejected by Shapeways after a week delay - definitely not fun when trying to design in fits and starts.

Seth’s light fixtures also come out close, though the holes in the diffusers weren't fully opened, and cutting the parts off the support structure was a real challenge.

Hints for New Owners

I've done six prints so far; generally, the parts that were larger and simpler printed well, and the parts where I was trying to be clever - printing small parts on the build platform, or aiming for tiny detail - came out less well. So far, I'm feeling very good about the Form 1.

One helpful hint: you don't need to fill the tank deep to be able to print parts. When the build platform initially comes down, it fills much of the tank space and highlighting why the maximum fill mark is so low. I've been worried about the resin curing between prints in our warm weather, and keeping less in the tank gives me some confidence I won't waste too much resin if that occurs.

Future Projects

So what am I going to do with this new printer? I've got a list of projects, but I suspect I'll be adjusting that list as I find what prints well and what prints badly.

One thought: how about making HO figures? Having a "model railroad club" set modeled after my friends could be a nice example of what can be printed. The real people scanned by Fredini over at Thingiverse could serve as great source material.

I need a bunch of HO SP flat cars for the lumber business on my layout. I've been hoping to find a good plastic car, but why not print some? I'd been planning on printing something similar to a plastic kit with a solid deck, but another modeler showed a flat car model on Shapeways where he only printed the underframe and metal parts, and glued a wooden deck on afterwards to complete the model. (See the GSC flat car model at Shapeways.)

Borcher Brothers building, North First St., San Jose

And finally, I want to use the printer to make architectural details I can't buy at the hobby store. The freight doors pictured above match a particular real building, and I've got a model waiting for six of those doors. I also want to build a model of the Borcher Brothers building supply. The real building, built in 1926, had an italianate design, but the terra cotta details are impossible to model. With a bit of care, I might be able to make those parts on the Form 1.