This has happened a few times: My machine, not an OX but my own build using OpenBuild parts, is behaving erratically. Controller: Chinese all in one board, 4x170oz steppers. 2.2kw Chinese spindle with VFD Cutting area 840x780mm Design in Sketchup CAM with Sketchucam Machine control with Mach3 Belts recently retensioned. No play in gantry. If I run the code with the spindle above the wood, everything tracks perfectly, so no gcode issues. Cutting Birch Ply 18mm, Spindle speed 18000rpm, X&Y at 2000mm/min (80ipm). Cutting depth 2.5mm per pass. Cutter is a 6.35mm compression bit from Amana. So what happened: First three 'laps' of the cut following perfectly. At 7.5mm cutting depth, the spindle just goes completely off course per the pic. No obvious change in noise of steppers or spindle. So, I carefully reset the position to the start point and rerun the code from scratch (after PC reboot). Spindle perfectly tracks the previous cut, then on the 4th lap, does exactly same thing in almost the identical place. What I do know: Cutter is probably not as sharp as a new one I had cut another shape to full 18mm depth (in 2.5mm) steps slightly earlier, followed by a 1mm closer full depth cut to clean the edge. No problems. Being plywood, alternating grains will mean unlikely that the bit grabbing the grain Cut where it happened is a sweeping left curve going from across the surface grain into the line of the grain. All motors felt cool to touch Please tell me how I am getting it wrong. I am very elementary in my use of Mach3. Know enough to make the cut, is there a way to see an error log. does it get feedback from the control board or the steppers if an error occurs? Thanks for your input.