Second Toolpath is Offset -0.5" along X-Axis

I bought a Shapeoko 3 XXL. Assembly and Hello World worked fine. I’m trying to cut two identical chair parts out of redwood stock with a #201 end mill (1/4"). There are two toolpaths. The first does a few pocket cuts and the second cuts the parts from the stock with a contour. No tool changes. The first toolpath cuts fine. If I pause and measure the positions of the pocket cuts, they’re accurate and match the design in CC.

The second toolpath, however, is offset -0.5" along the x-axis. The width/height of the part are correct, just shifted left. The feed rate is 60"/min, RPM is 18000, and plunge rate is 12"/min. There’s no vibration/wobbling/excessive noise while the machine is cutting.

The simulation in CC looks correct. I read some other troubleshooting steps to check that V wheels are tight, that set screws on the motors are tight, and that belts are tight. These all look fine.

Anyone have other ideas to try?

A couple of considerations here:

  • cutting a slot as narrow as the endmill results in near constant 100% tooling engagement — best practice is to add geometry and cut as a pocket down to tab depth at least:
  • leaving a roughing clearance and taking a finishing pass will help with final dimensions
  • if you haven’t calibrated for belt stretch, doing so will help with the evenness of parts:

Thanks for the tips. I haven’t done belt stretch calibration, I’ll do this next. I’ll update my design to add an offset pocket, then a second cut. I’ll post back here with the results.

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Also double-check that the machine does not hit the left or right rails during that final cutout, which would result in lost steps on the X axis, shifting the rest of the cut along X by the same amount.

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