Sunday, July 18, 2010

Two Makerbot Side Notes

1) Tricking out a Makerbot is insanely easy. Cold cathode lights intended for lighting PC cases are dirt cheap ($6 at Fry's), and the 10 inch tube lights fit neatly in the Makerbot case. They were too long to fit in the build area, so I drilled holes in the panel between the build chamber and power supply, and stuck the lamps up into the build chamber as far as they'd go. I used blue and white lights because that's what's available, and they both trick out the Makerbot nicely and provide some decent light to see the model being built.

2) I had a lot of problems getting my Mac laptop configured correctly for printing to the Makerbot. Part of that's my own fault; that laptop has been used with three devices expecting a USB->serial converter. I use the JMRI model railroad software to configure the decoders in my model railroad locomotives. I've installed USB->serial drivers to get a Cricut computer-controlled paper cutter working. Finally, I've got the Makerbot and its serial interface. Most of my problems were caused by JMRI expecting the various Java libraries for controlling serial ports to be installed with the default Java installation on Mac OS X, but both ReplicatorG and the Cricut software ties the drivers to the Mac application.

So this weekend, when I needed to get the JMRI software running, I found the Makerbot configuration was somehow messing things up. I finally got it working after deleting all the various serial port jars and jnilib files from different directories, but kept having problems until I finally got rid of a Java jar file in some directory that I'd renamed from "RXTXcomm.jar" to "RXTXcomm.jar.unused". It looks like Java ignores the file extension, and if there's a file that looks like a Jar file, Java will read it in. Next time, I move all the unneeded files well out of the way.

Tuning the Mendel, and comparing it to Makerbot

"Two three-dee printers? You don't think he's planning on breeding them, do you?"

Sorry, I've been waiting a long time to be able to use that punch line; I'd seen it on a for-sale ad for a maligned Sequent mainframe that had one taker from a university that already had one of the beasts, and the idea that someone *wanted* two of them really frightened the seller. But it's true - I've now got two working three-dee printers in the house. Luckily, they're not breeding, as we're cramped for space as it is.

The Mendel's running, and it's printed some useful stuff. It's still not perfect; model heights are still too short, and there's no place for the power supply. But it's been an interesting experience getting it running, and it's been interesting for me to compare the Makerbot and Mendel experience.

First, details of what I've done with the Mendel. First, like the Makerbot, I'm using 0.5 inch plexiglass for the build surface; I find the ABS sticks well to this cold as long as it's clean, and the completed prints come off decently with a putty knive or chisel. I'm using the Mendel without a heated build platform, and my 6 inch wheel I tried last weekend did warp pretty quickly. I'll have to try some anti-warping tricks (like the lattice base on the Brio track model on thingiverse) if I want to build larger models.

I'm also using standard Makerbot electronics for compatibility with my Makerbot. One annoyance is that the Mendel is intended to be driven from an external single-voltage power supply, but the Makerbot electronics come standard with a 20 pin PC motherboard plug. The Makerbot has that nice box to hide the power supply, but the Mendel has no place to hide the power supply. For now, it sits to the side of the Mendel.

It's hard to adjust the Z axis height on the Mendel; on the Makerbot, I'm used to tweaking the Z axis pulleys or belt to adjust the printhead height. A Z axis knob (like this) is a necessity.

That brings me to philosophy. Getting the Mendel running has been a fun experience; it's freeing to know that I can basically build and tweak all the different parts of a printer (including making a new extruder based on the Makerbot parts, and figuring out how to get it to fit in the existing Mendel). I'd realized when building the Makerbot that there's nothing particularly sophisticated about the mechanism for the 3d printer; all the magic really is in the software that figures out where to move the extruder, and how fast to move it. Beyond that, the mechanism is pretty simple, with reliability being the only big concern.

But building the Mendel also pointed out that while the mechanism is easy, there were all sorts of design tradeoffs that the Makerbot team made. The smaller print surface makes for a nice enclosed box design and minimizes the problems with warping. The enclosed box style provides a place to hide a standard and cheap power supply. The placement of the power supply and various Makerbot circuit boards seems easy, but when I had to figure out placement and wire length constraints when assembling the Mendel, I realized someone had to think hard and long about how to arrange the Makerbot, and where to run wires, and how to avoid boards getting in the way of the mechanism. The design of the Z axis makes it really easy to move the printhead large distances, moving it up when disassembling the print head or trying to get things set up, and moving it quickly down to build surface height to start a build. Makerbot's removable build surface simplifies getting a putty knife under a sticky print, but with Mendel, I need to be careful the build platform doesn't move as I pry.

Someone had to think of all those little details on the Makerbot, and they did a pretty good job. I'm happy I've built my Mendel, but I think the Makerbot's still going to get more of the work just because it's easier to put on top of the bench, and easier to adjust.