Probe / mill safety feature for upgraded X Controller

Hi everyone,

I’ve been working on designing and building my upgraded X Controller for awhile now and just today I had an idea that is simple, but effective for preventing something terrible. Maybe I’m more a düfus than most, but on more than one occasion I’ve gone to mill a PCB after probing and forgotten to disconnect the alligator clip on the V bit. It will be child’s play to program a controller to disallow the activation of your router/spindle if the probe pin is at logic LOW. In fact, I’m of the opinion this should be default in the Inventable’s distro of GRBL. My 2¢.

Clip on the bit should be connected to ground, not an input pin?

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That, actually, does solve a problem or two. I’ve read here and there that if you connect probe to the bit you can have a problem with false trigger. The router/spindle body can be either ground or neutral, so some people have said disconnecting your router is a way to make that work. Connecting the probe pin to the workpiece and DCCommon (please don’t actually use ground) to the bit solves that problem.

@PhilJohnson, it’s of course your call when to say “this is safe enough.” It’s just happened to me at least 2 or 3 times, I’d rather spend 10 minutes programming something clever like “if you see the machine probing and then it stops moving for >1 minute, turn off the stepper motor power until I press HOLD FEED button twice to indicate I’ve removed the probe clip”. And you certainly can bubble wrap the world :wink:


Get yourself a dust shoe. Best insurance against it I’ve run into. Can’t fit the shoe on with the clip in place!