Friday, December 18, 2009

I Trust My Makerbot / Making Model Buildings

Makerbot's much more fun when you trust it enough to leave it alone for 30 minutes.

Last weekend's experimentation made a huge difference; with the cable to the extruder replaced, I'm having every print work fine. The Brio train track was one of the first things I tried, and I was amazed that the first print went perfectly. The Brio track's also interesting because it uses a lattice structure on the lower layers to minimize warping. When there aren't lots of uninterrupted threads of plastic, shrinkage won't cause the part to curl.

With such good luck, I moved on to one of the projects I'd bought the Makerbot for: could I use it to build model buildings for my model railroad? Specifically, I wanted to print out Spanish Revival style building facades. The curves and layers would be difficult to do by hand, and much harder to do repeatedly, but easy to do with the Makerbot.

Here's a quick look at my first print. The print is 90mm (3.5 inches) across and 70 mm (2.75 inches) deep, and was intended to be around 3 mm thick. It's getting close to the maximum width for the Makerbot; the stock build platform is 100 mm square, but the raft for this print - the crosshatched layers of plastic put down first to hold the model to the surface - is 102 mm. I found my machine could move 110 mm, so I cut a new build platform out of Plexiglas to do larger objects. My first two prints for the building facade failed quickly; the pieces warped horribly within a few layers, and usually bumped the nozzle as they moved around. Bad.

But the Brio track hadn't warped. I wondered if I could break up the long side pieces so that the top layer couldn't pull across the piece to cause the warp. Back in SketchUp, I made the piece twice as deep, and cut some wedges out of the thickened back side perpendicular to the warping.

The new design printed perfectly - no warping, and very little problem with the print. I even managed to print four more over the next couple days. Each print took around 35 minutes, and used 10cc of plastic (or about 20c worth). Best of all, these were the first prints I'd done on the Makerbot where I felt like I could walk away for several minutes without worrying if the printer had stalled and was spewing out hot plastic at one spot.

Warping parts is a big deal in the Makerbot community. The warping occurs because the styrene plastic shrinks about 2% as it cools, pulling at the lower levels and causing the part to cup and pull away from the build surface and first "raft" of plastic laid down. In the best case, the parts end up with a rounded base; the lower levels warp, but later levels get affected less by the warping and build up new flat surfaces. In the worst case, the part curls enough to foul the machine. There have been lots of potential solutions. Some think that changing the plastic used will help. Others are experimenting with heating the build platforms to 60 degrees Celsius so less shrinkage and warping occur. My experiences make me wonder if some simple tweaks to the design might be enough.

My printed building fronts are for a 1920's drive-in market. These weren't the drive-your-car-in markets of the fifties, but the predecessors of modern strip malls - inexpensive buildings put up on corner lots along the new roads leading out to the suburbs. The markets had a pretty standard format: one market, one greengrocer, one butcher, a baker. Each was an independent business with an individual space, but together they were just the place to stop for groceries on the way home. Like many 1920's and 1930's buildings, they often used some extra architectural detail to draw in drivers, and Spanish Revival was a popular style back then. Longstreth's book shows pictures of drive-in markets around Los Angeles, but they appeared elsewhere in the U.S., and were certainly seen in the San Francisco and San Jose area that I model. (The old photo, in fact, is of a drive-in market on Telegraph Ave. in Berkeley, CA. It's long-gone, or at least remodeled.)

I'm planning to glue the building fronts together to make an "L" shape to fit the lot space, and my usual model building supplies for the back walls. The Makerbot surfaces are still pretty rough, so I'm planning on using spackle to fill in the rough spots and simular plaster. Some of the detail, such as the sawtooth row above the arch, will stay to simulate some of the details found on the actual buildings.

Sunday, December 13, 2009

Better Luck

I spent the day trying to figure out what might be causing my hangs during printing. I started by trying to print a simple object - a leg for the Makerbot. Like the maker of these legs, my power supply had a fan pointing down, so I needed to raise the Makerbot up a bit to get air to the power supply. My legs are shorter than pattywac's; I didn't want the Makerbot raised up so high.

I ended up trying to print 13 legs, and 8 were usable. My first four prints went great, then things went downhill from there. The two conditions I tested were (1) turning off the fluorescent lights above the workbench, and (2) using a real Ethernet cable for the motherboard-to-extruder cable, rather then the home-crimped cable I had been using. I also routed the extruder cable away from the USB line and the Z stepper motor wires.

Results: with the lights off and the cable replaced, I had three of four prints go fine, with the fourth hanging at the 13 minute mark just as the piece finished printing. When I switched back to the old extruder cable, I got an immediate failure, then two successes. Turning on the fluorescent lights caused a couple of immediate failures, but things didn't improve after the cable and light were replaced. I wondered if something was overheating after several prints, but couldn't find any unusually hot pieces.

Still, I had pretty good luck today. Here's pictures of my Makerbot legs, sitting on their own. I modeled these in SketchUp Pro, then used Blender and skeinforge to convert them to a printable form.

I also tried printing building fronts as a model railroad project. The Makerbot did a great job with the curved lines of a Spanish Revival building, but the piece warped pretty quickly and eventually jammed the extruder nozzle. I even tried printing on a piece of 0.060 inch sheet styrene, but the extruded plastic only stuck a bit better than on the acrylic.

Saturday, December 12, 2009

Makerbot Hiccups

It's interesting reading the Makerbot list at Google Groups, because you find out that some people seem to be having no problems at all with their Makerbot, and others seem to be having no end of problems. My particular problem has been builds hanging while the extruder keeps extruding. I've seen different guesses at the cause:

  • #1: The USB/serial cable can't send data quickly enough (supposedly solved by printing to the SD card on the Makerbot motherboard).
  • #2: The ReplicatorG control panel is up, so it's constantly polling the extruder for the current temperature (or the "monitor temperature" setting in ReplicatorG's preferences is set); closing the panel or un-checking the setting supposedly solves that. I've also guessed at a few.
  • #3: The computer sleeps or slows down, and loses contact, solved by turning off sleep.
  • #4: Electrical noise on the USB or extruder cable causes the Makerbot motherboard and extruder to lose contact.
  • #5 Noise on the USB cable causes problems. (In both cases, move the cables away from the higher current stepper motor wires.)
  • #6 Too close to fluorescent lights. (This might actually be an issue. My first few prints worked fine, and most of my problems have been with the Makerbot on my workbench underneath a fluorescent lamp.)

None of these has made much of a difference for me. My first print usually goes well, and then I'm fiddling around trying to get another good print. Tonight's adventure was printing these legs for the Makerbot. Each is about a 12 minute print; to get four good ones, I did around twelve total prints tonight, some failing late in the print, others hanging within a minute or two. I still don't have a handle on what's going on, but I'm going to keep looking.

I did have one bit of good news. I'd had problems in the past because a well-adhering part could actually bend the 1/8" plexiglas build surface and cause the part to warp. I hold the plexiglass to the wooden build platform with double-stick tape, but several pieces of tape weren't enough to keep the plexiglass from bending.

Luckily, I found a scrap of 1/2" clear plexiglass at our local plastic shop, cut it down to 110 mm square (or 10 mm bigger than the default build surface!), and started printing. The leg models I was using didn't have rafts, but I found they still stuck wonderfully to the new plexiglass and gave me some nice, unwarped parts. Woohoo!

Making the new build surface was easy. I cut the new piece to rough size with a hack saw, then filed and sandpapered the edges smooth. The official Makerbot build surface has a grid of lines scratched in it, so I scratched some similar lines in my piece - a few for adhesion (which didn't seem to matter), and a pair of lines in the center of the piece so I could position the build platform at the start of the build.

Regardless of the headaches, I've got four legs for my Makerbot. I'll still need to file them down to equal height (one's a bit shorter), but they're almost done.