Project-Insanity

The calibration plate below was made by Chris at Blue Ox CNC: http://stores.ebay.com/chrisclub1?_rdc=1 The calibration plate, as I like to call it, is 4cm x 4cm square. The edge of the plate, when butted up against your stock, is exactly 10mm offset from the sides. When I started down the probing road, I had a hell of time getting my Arduino not to trip the probe constantly. I ended up adding a 100nf 50V ceramic cap between the Arduino ground and A5 pin and a 10K ohm resistor at the end of the probe. The probe wire is shielded and the braided shield is grounded to Arduino ground. Literally a full day of trying different combinations! Ug. Anyway, once I had it up and running, I followed after these fine gents to setup a fully automated XYZ zero in Universal Gcode Sender. Martin Barfoed: https://www.youtube.com/watch?v=0_tiq… and Charley Thomas: https://www.youtube.com/watch?v=thmX5… Also thanks to Kyo for inspiring me to build this amazing CNC based on his Sphinx design! https://www.youtube.com/user/KyoShino… To calibrate all three axis at once, center the probe just above the cal plate and hit the macro button in UGS. The code below automatically sets work X, Y and Z zero. Some of the settings work for my plate and bit size. You'll have to play around to get it work for you.

Copy and paste the following command string into a macro in Universal Gcode Sender: G38.2 Z-15 F100; G92 Z2.8; G91 G0 Z3; G91 G0 X-30; G91 G0 Z-6; G38.2 X15 F100; G92 X-13.175; G91 G0 X-3; G91 G0 Z6; G91 G0 Y-30; G91 G0 X30; G91 G0 Z-6; G38.2 Y15 F100; G92 Y-13.175; G91 G0 Y-3; G91 G0 Z6

Below I'll try and explain the Gcode so you can understand and modify for your own cal plate and preferences:

G38.2 Z-15 F100 G38.2 is a probe command which means, seek until the probe circuit is closed (Arduino ground to pin A5). Z-15 means drop the Z axis down a maximum of 15mm (metric in my case). Of course, this travel should be interrupted by probe contacting the plate surface. F100 is the probe travel speed. You may want to slow yours down, but I find 100 works fine.

G92 Z2.8 Now set Z work zero (not machine zero). Compensate by 2.8mm, the thickness of the calibration plate. In other words, the actual stock top.

Semi colons separate command sets (not sure if that is the right nomenclature.)

G91 G0 Z3 G91 G0 I believe is a rapid move, the Z axis 3mm up or positive direction.

G91 G0 X-30 Then rapid move 30mm left, or negative X direction.

G91 G0 Z-6 And drop Z down 6mm in preparation for X probing.

G38.2 X15 F100 Now probe for X side of the calibration plate.

G92 X-13.175 Set X work zero. Add the thickness of the calibration plate (the edge of the cal plate to the wood stock is 10mm), then add the radius of the bit (half the diameter) 3.175mm. (1/4“ dia bit = 6.35mm). X zero is now set to the left edge of the stock minus half bit diameter.

G91 G0 X-3 Pull bit away from the cal plate 3mm.

G91 G0 Z6 Raise bit up 6mm. (I have since eliminated raising the Z up for this move to the front of the plate)

G91 G0 Y-30 Move toward front of the plate 30mm.

G91 G0 X30 Move right, in the X positive direction, 30mm.

G91 G0 Z-6 Drop the bit back down 6mm in preparation for Y probing. (Also eliminated.)

G38.2 Y15 F100 Probe Y axis.

G92 Y-13.175 Set Y work zero to thickness of front of the calibration plate (again, 10mm), plus radius of bit (3.175mm). Y work zero is now set to edge of stock minus half bit diameter.

G91 G0 Y-3 Pull forward off work, 3mm

G91 G0 Z6 Raise bit 6mm.

Now, when you hit the “Return to zero” button in UGS, the bit will sit on your stock with the bit perfectly centered on the front corner. Of course if you like to set work zero to the back corner, you'll have to change things around a bit.

Project-Insanity

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