Friday, May 28, 2010

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.



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.

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