Project cut too deep into spoilboard, and I don't know why

Shapeoko rookie here.

This afternoon I milled some hold-down clamps out of plywood. I thought I was being real clever in my approach (:slight_smile: ) by setting Z-Zero on the spoilboard, which is something I’ve never done before. The thinking was to avoid cutting anything more than a shadow into the spoilboard, which I confirmed to be flat and level. I broke the job into two separate G-Code exports. One was for everything that didn’t cut all the way through the stock, which was just pocketing. The second was for all the through-cuts.

For the through-cuts, two tools were involved. The #102 cutter went first and the depth was perfect. I was then prompted to switch to the #201 cutter, which I did (I have a bitsetter). The resulting cuts were ~1.5mm too deep. I tightened the #201 cutter nice and tight, and the collet nut was still tight at the end of the job.

The only things I can think of that could have gone wrong are 1) The bit wasn’t tight enough and vibrated out of the collet just a bit, 2) Something went wrong with the bitsetter. I’m sure there are other things as well, but I’m not knowledgeable enough to have thought of them yet.

The machine is a Shapeoko 4XXL. Attached are the c2d and G-Code files.

Any thoughts or ideas will be much appreciated.

Thank you!
Holddown clamps.rev02.c2d (699.6 KB)
Clamps Rev 2 (192.2 KB)

There’s nothing like that in the file:

Possible causes:

  • electrical issue — check the wiring and connectors
  • mechanical issue — check the machine mechanically

Thanks for checking out those files, Will. Just prior to this carve I did a project with an Advanced V Carve toolpath and everything worked fine. Immediately after I did a project with V Carve, Advanced V Carve, and Pocket toolpaths, and again everything worked fine. With that it seems an electrical issue isn’t likely, nor an overarching mechanical issue. I’ll pay closer attention for tool slippage, perhaps by placing a mark with a Sharpie on the shaft of the tool so I can tell if it’s moving out of the collet.

When you switched to the #201, were ALL the cuts with that bit 1.5mm too deep or did the depth change during the cut. If the depth changed that is evidence suggesting a bit-slip. I (unfortunately) have had my share of bit-slips. The last two have been upcut bits and after inspecting the collet I blamed myself for not making sure the collet wasn’t jammed with dust.

Dust just stacks up on the very top of your bit (inside the collet) and when you remove a bit the dust just dumps into the collet.

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Good question, and good idea! I didn’t think to check that, but I’ll measure. Thank you for pointing that out.

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