Our Shapeoko was working just fine until a couple of days ago. But now, when we tried to cut 1/8" polycarbonate, it went through the entire material on the first pass even though the tool path had it starting at a much more modest depth. We reset the machine and restarted the cut a number of times. Sometimes it starts out fine and then the cut depth suddenly increases without reason. A couple of times the depth increased so much that the bit cut into the MDF. We use a bit setter, so this should not happen.
worn lead-screw/anti-backlash nut needs to be adjusted
Best test is to jog the machine to the center for all axes, then up/down, then with the machine at the center and powered up, grab the tip of a probing pin installed on the tool and try to shift it in all directions — investigate anything which allows it to shift.