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.

Next Project?

So the Mendel printer's almost done. What's on my list of potential projects?

• Build a model of a railroad handcar, using the Makerbot to print all the cast and fabricated metal parts, but using wood for the parts that would be wood on the real thing.
  
• Print some large railroad wheels, either for the handcar or for some other project. How large can I go?
  
• An HO model of a 1950's style burger stand (like this Dairy Queen
  
• More ergonomic throttle case for the model railroad throttles I use.
  
• Print a full railroad car in HO. (Requires the Mendel so I can print a 6" long piece.)
  

RepRap Mendel Printing!

Once I'd printed all the parts for my Reprap Mendel printer, I thought I was close to done. In reality, it took me another two months to finish: getting the stepper motors, tuning the mechanism, and (finally) making a new extruder for squirting out the plastic. The last step was the hardest; the Makerbot plastruder won't fit on the Mendel, and the new heater barrel needs to be longer than the Makerbot one.

After a bunch of assembling, machining, and cursing, I finally had my Mendel printing tonight. The X axis is still slipping a bit and I'm having problems with dimensions (probably because of friction on the X carriage), but I printed several of the 20 mm test cubes in a row, so it looks like the Mendel's printing.

Woohoo!

Details:


For the Mendel itself, it's mostly built as described in the instructions, but I did make two changes. I was going to use the Mendel's long drive gears for the stepper motors, but filing flats on the stepper motor shafts was too time-consuming. I instead went to nophead's Mendel pulleys, drilling each to be a press fit on the stepper motor shaft. So far, they've worked fine with no slipping. Each required a little cleanup with a grinding bit in a Dremel moto-tool to clean up extra plastic on the gear teeth. I also ended up fabricating the X axis motor bracket from sheet plastic (1/2" thick) because of problems printing the part.

For the extruder, I used Zaggo's Printruder II with a Makerbot gear motor, homemade printer barrel, and homemade gear pulley. I turned the pulley from brass rod on a lathe, cut the teeth with a file, and drilled and tapped a hole for a set screw. The teeth weren't large enough to grip the filament at first, but some coarse filing resulted in ugly, but very functional teeth. I used a spare Makerbot heater barrel and a new insulator barrel turned from PEEK rod for the heater. The insulator barrel needed to be two inches long (as compared to 35 mm/1.3 inches) to reach through the Mendel's X carriage. Turning the PEEK was remarkably easy; it machines easily and doesn't melt too quickly. It's also expensive at $30/foot, but I much prefer being able to make my own insulators whenever my Makerbot breaks. I couldn't find screws long enough to reach from the heat shield to the printruder body, so I took more brass rod, drilled and threaded it through, and the used two 1.5 inch 4-40 screws to hold the heat shield and pull the barrel to the printruder body.

I've only printed so far with the Mendel using the Makerbot's electronics. If it looks like it's printing well, then I'll take the plunge and buy another set of the Makerbot electronics. I had to solder extra-long wires on all the stepper motors and buy new Molex plugs to fit the Makerbot stepper motor drivers. The extruder controller seemed like it wanted to be closer to the Mendel, so I mounted it as shown.

What do I think of the Mendel so far? It's a mixed bag. I'm really pleased I got this running, and that I was able to fabricate many of the parts (heater barrel, extruder gear, etc.) I'm really curious to see how it does at printing large objects. The Mendel's generally quieter than the Makerbot. On the minus side, the Z axis is a lot slower than the Makerbot because of the large gears at the base of the Z screws. It's difficult to get to some parts; removing and reattaching the extruder (at least with a Makerbot-like heat shield) is more work than on the Makerbot. I also missed the Makerbot's exposed Z axis belts, for it makes minor height adjustments when printing the raft easier. It's possible to adjust the height by spinning the Z screw gears, but they're hard to reach and turn.

More as I get some experience with the new printer.

When in Doubt, Build a Mendel

Okay, I don't know why I'm doing it.

I've been having fun with my Makerbot. I've had occasional interesting projects, and occasional uninteresting projects. I've been a little frustrated by the maximum size the Makerbot can handle, but not that frustrated. I also tend to be annoyed at the people who use machine tools only to build handy tools for machining.

But for some reason, when I saw Spacexula's Mendel Production Set, I thought, "Hey, that'll be fun, let's try printing parts to build another 3d printer!"

Now, to be fair, I was interested in how he'd packed several parts onto each print. When all my Makerbot prints have been 45 minute waits for a single part, it was pretty cool for the first print to give me seven or eight decent parts. From there, I just kept going, slowly filling a shoebox with the completed parts. Then I ordered the various hardware, and... well, now, I've got the mechanism for a Mendel almost done and I'm kind of curious what I'll do with it.


It took about two weeks of printing to get almost all the parts done, with several prints on weekends and (if I was lucky) one or two complete prints during the week. I had remarkably good luck; maybe 60% of the prints worked fine the first time. I had some other problems with prints curling and jamming the print head. Some of the larger parts such as the lower carriage went really badly, with too much plastic at screwholes jamming the printer. I even resorted to using a failed print on the carriage when I couldn't complete a full print.

I assembled the Mendel this weekend after making a big parts order to McMaster and the bearings here. Both shipped immediately and arrived quickly. I still am waiting on the stepper motors (which I'm getting from Alltronics - I'll let ya know how that goes), and once those are running, I'll see how my mechanism works.

Helpful hints for building a Mendel:

• The Nyloc locknuts are a bear to work with, hard to put on and a pain for disassembly. I ended up falling back to regular M4 nuts for connections that didn't look like they were liable to shake loose. If I do have problems, I'll either add a second nut or a Nyloc nut.
  
• The ground steel rod is hardened, and my hacksaw wouldn't scratch it. I ended up using a Dremel moto-tool with a cutoff wheel to cut the hardened outside layer of the bar, then used the hacksaw to cut the bar.
  
• I ended up needing to drill out all the screw holes to get the screws in. When screw holes need to line up in parts, I used the machinist trick of drilling out the top piece separately, clamping all parts together, then using the top piece as a jig to keep the holes aligned.
  

It's also been interesting to compare the Mendel to the Makerbot. If I had to choose Makerbot or Mendel, I'd go for the Makerbot - assembly was quicker, it feels more robust, and various design points just feel better. The plastic bushings and guide rods for the X and Y axis require much less tuning, and the magnetized build platform makes it easy to print, then pull the platform out to scrape the print off the build platform.

The Mendel wasn't that hard to put together, but the printed parts sometimes annoyed me because they weren't as precise as machined or laser-cut parts. The Makerbot went together much better, and feels more robust, while I keep wondering which printed parts will fail first. For places where accuracy matters (such as on the guides for the X axis assembly), a little bit of debris or extra raft material can throw off rod spacing, and makes me think I'll have problems with alignment and friction.

Well, THAT didn't work!

Definitely no luck with the homebrew heated platform. The 10 ohm nichrome wire pulled about an amp of current (not surprising for a 12 volt power source), but took 10-20 minutes to heart up. I poked a wire into the silicone between the layers of glass and dragged out the middle of the wire, and soldered a new wire on. By connecting the new midpoint to one terminal and the original two wires to the other terminal, that meant I had two wires in the platform that were half as long, and it drew (not surprisingly) 4 amps... and started heating the plastruder circuits too much. (It heated up really fast, though!) I then just connected up one side for 2 amps of power... and the glass quietly cracked.

Next step: two amps of current seemed ok for the plastruder, so if I remake the build platform (and try glass again), I'll try stretching two 10 ohm / 16" nichrome wires inside. The platform can definitely use the extra nichrome to spread out the heat source and hopefully keep the glass safe.

Heated Build Platform

After seeing some of the great results folks have had with heated build platforms (such as Hydraraptor's groups of pieces, I wanted to try one too. I'm mostly interested in cutting the warping of long parts, avoiding printing rafts, and experimenting with the nichrome wire.

Here's a photo of my build platform; I based it on Hive76's design that they're selling through Makerbot. I far as I could tell, they use a couple pieces of glass, nichrome wire, and silicone sealant to make their build platforms.

I tried the same, though I sealed all the wires between the two layers of glass with tons of silicone. I used the same 10 ohm piece of nichrome, soldered the ends to longer pigtails of copper wire. I then cut two pieces of 4" square glass with a glass cutter and straightedge. I used dots of silicone and carefully placed weights to get the wire in place. I also added a spare thermistor and wires for measuring temperature, then covered everything in silicone, added a spare piece of copper wire at the far side of the platform to keep the pieces of glass parallel (because of the soldered connections on the near side), then smushed the two pieces of glass together.

I also used a bit of Radio Shack pre-drilled circuit board for the circuitry to connect the thermistor to the spare A6 analog port on the extruder controller.

I found 16 inches / 10 ohms of nichrome wire isn't enough to get sufficient heat; it took around 15 minutes to heat the glass to 55 degrees Celsius, and while the ABS would bond to the glass at hotspots above the wires, the plastic wouldn't stick to the glass elsewhere, even if I made sure the glass was clean and free of grease.

Looks like I'll stick with my 1/2" plexiglass build platform I currently use, though I might take another pass at the heated build platform in a few weeks.

Also this weekend: my original extruder nozzle/heater died with a broken wire, so I made a new one from spare parts. The original one put in a fair number of hours. I also found that ReplicatorG version 13 (for the heated platform support) also is much quieter about moving the stepper motors - that was a nice surprise!