Tim Hatch

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Cartesian Robot Progress 16 Jul, 2010

I’ve started once again to work on my goal of building a RepRap which started almost three years ago when I was still in Texas. When I was there, I built half a McWire bot with Jesse’s help — the frame, and X/Y axes were finished when I moved and Palmer contributed parts from a BfB extruder.

McWire with Z axis built

Last weekend, I finished out the Z axis, with some minor changes. I went with locally-available U-channel aluminum which was thinner (1/16” vs 1/8”) than the rails ordered from McMaster. During cutting, I also managed to introduce some scuffing on the running surface which I mostly sanded out. I hope these won’t affect the friction of the PFTE bearings (but if it does, I found the 1/8” U-channel in the meantime).

The hardware mounting the Z-axis is a mix of imperial and metric, with lots of washers adapting for different size parts — mainly because I ran out of metric parts from my initial order, but also because it’s difficult to find 5/16” machine screws with a bevel head suitable for countersinking. Ace Hardware doesn’t carry any 5/16” with a bevel here, Home Depot has them but only in specific sizes, OSH only carries them >2” long, but I managed to find the best selection at the tiny San Andres Hardware on Micheltorena (they’re slotted, not phillips like the rest, but oh well).

I have a completed set of early RepRap electronics so I’ve run some quick tests and all the stages move as they’re supposed to. Excessive torque on the Z-axis will knock the nut out of the pipe clamp, which makes me wonder if it will also move over time and require re-homing even with lower torque. Next on the list is to finish some extender cables so I can put all the stepper controller boards in one place. I’m using 18-ga sprinkler wire for the stationary X and Z axes, but some super-flexible 16-ga speaker wire that Berto had leftover from a project for the Y axis (which is the only motor that moves during operation).

I’m using the stock leadscrews for now (1/4 × 20 stainless allthread) but intend to move to an alternate drive system after I get the electronics hooked up and a couple of test millings. The primary ones I’m considering are:

  • ball-chain, which I’ll cover in an upcoming post
  • wooden auger, although I’ll need to unbox my drill press
  • larger (3/8” or so) allthread, since it’s coarser (16 tpi vs 20)