Taking the Gm-17 out of Nop...

Reducing the vitamin content of the Mk I Nutjob extruder...

These past few months have been very frustrating for me vis a vis Reprap. My day job has got intense to the point where there is little time for Reprap and worse still, the little time there is finds me mentally exhausted and incapable of working efficiently on Reprap work. In a less stressed time I could have designed and built the Mk I Nutjob over a couple of weekends. As it is, I've been working on it for since the New Year. Focussing has been hard.

Last weekend, things began to come together. I now have an assembled polymer pump using a nut as the threaded pump and it appears to work pretty well.

The pump has no problem biting into and moving ABS, HDPE and homopolypropylene. With the 228:1 standard gear ratio it moves a bit over 7.3 mm/minute. If I reduce that to 51:1 using the Dietl gear kits that Solarbotics sells it appears that I can extrude at a rate of 15-20 mm/sec.

Nophead's GM-17/tin can stepper hack really delivers the power. I ordered four more GM-17s and the Dietl Rome gear sets to work with.

Having done that I looked at what Nophead's hack was actually costing. The GM-17 costs about $5-6, the Dietl gear set about $4 and the tin can stepper from Jameco about $7. Figure $17 dollars to get a lightweight, powerful, stepper-driven gearmotor. I can get a NEMA 17 that does the same job for that price without a lot of trouble. It's heavier, but hey?

That got me to thinking about the GM-17 gearbox. I don't use the little coreless electric motor. I'm paying $10 for a gearbox with about as much plastic in it as one joint of my little finger.

Quite some time ago, I was milling small gears and racks. They weren't very good. Since then, I've got a lot better at milling, but I haven't gone back to milling small things again. Before work this morning I decided to see if I could do a better job with my increased know-how.

In fact, I could.

What you see is a pinion gear suitable for pressing onto the 2 mm drive shaft of the tiny tin can stepper used in Nophead's hack. The cylinder under it is a piece of 3 mm filament. The pinion has a pressure radius of 5 mm.

Looking at the success of Nophead's hack, it is obvious that it is best not to have a lot of mass in the initial, high-speed gears in a gearbox. While my 10 mm pinion gear isn't as tiny as the GM-17's, it weighs a small fraction of a gram. It is also the hardest gear to mill.

I did some partial cuts of pinion gears with higher cut quality. My z-axis on T2 is a bit cranky this morning, however, and I wasn't able to successfully complete them before I had to quit for work.

Interestingly, gears of this size and thickness only take a few minutes to cut.

I will be using the GM-17/tin can stepper hack to work the bugs out of the Mk I Nutjob. Afterwards, however, I will be taking a very hard look at taking the GM-17 gearbox out of the vitamins column of Tommelise 3.0 Sampo.