Monday, January 25, 2010
Getting there with herringbone rack and pinion
I finally hit a break in my day job and after sleeping the clock around beginning Friday afternoon was able to get back to my Reprap work. I'd been working with herringbone rack and pinion design and had begun writing Art of Illusion scripts to generate this kind of technology. I'd done most of the rack script a few weeks ago, but I needed to be able to design herringbone gears a bit more efficiently.
Finally, on Sunday the scripts for the racks and gears began to come together. After a considerable amount of feeling around I found that I could reliably print an 8 mm radius, 12 toothed gear. Connecting such a pinion directly to a 1.8 degree step NEMA 17 gives me a 0.25 mm/ step on the axis without microstepping. I then designed a 32 toothed gear which let me get that resolution down to 0.094 mm/step. You can see the layout here...
The NEMA 17 turns the 12 toothed pinion at the top of the picture. It turns the 32 toothed gear which shares an axle with a second 12 toothed pinion which engages the rack. It's simple, easy and quick to print and doesn't backlash if you apply just a slight bit of compression to the gear train. My next task is to design a printable axis assembly to house it. My goal is to get rid of the skateboard bearings, too.
The scripts are in a lot better shape, but they're still not really ready for prime time.