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Archive for April 29th, 2013

Makergear M2: Z-minimum Switch

The best orientation for the Z-minimum switch seems to be slightly angled back:

M2 - Z min limit switch

M2 – Z min limit switch

I used an M4x0.7 socket head cap screw for the height adjustment, with a Nylock nut below the stage:

M2 - Z min limit screw

M2 – Z min limit screw

The assembly instructions show a hex head screw, but the item numbers don’t match the BOM listings. The SHCS lets me hold it firmly in position with the ball-end driver provided in the M2 tool kit while adjusting it:

  • 1/4 turn (the handle is square-ish) = 0.7/4 = 0.175 mm
  • 1/6 turn (the shaft is hex) = 0.12 mm
  • 1/12 turn (you can do it!) = 0.06mm
  • less than that is probably fooling yourself.

I printed a pair of tomlombardi’s  7 mm wrenches, which work well for adjusting the Nylock nut underneath the Z axis stage:

M2 - 7 mm wrenches

M2 – 7 mm wrenches

The left end of the top wrench didn’t adhere to the glass plate, but the business end of the wrench came out OK.

I adjusted the screw to trip the switch with the nozzle 1.0 mm above the platform, then feed that offset in using a G92 Z1.0 instruction in my customized Start G-Code.

However, the most accurate way to set the switch height involves measuring the as-printed thickness of the skirt extrusion around the object. The average value should be 0.25 mm (for my current slic3r settings, anyhow) and all sides should be equally thick: adjust the screw to change the average and adjust the platform screws to remove any tilt. You’ll quickly accumulate a pile of skirt threads, but they make good tchotchkes when you give a presentation on your new toy:

M2 skirt extrusions

M2 skirt extrusions

You could fiddle with the G92 value to make the average thickness come out right, but I favor making the machine as accurate as possible, so that the software begins from a known-good mechanical setting.

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