Initial cut way too deep

CNC Machines Shapeoko 5 Pro
1

Hi All–

I’ve run this file four times now, each time carefully setting the Z height and, after the first one, doing the rapid jog to 6 mm above the surface to test the setting, which was correct. Three times using the Bitsetter and once manually using the paper technique. In each case the bit dove into the piece to a depth of ~3mm on the first pass. Subsequent passes increased depth by the expected sub-millimeter increment. If I hadn’t hit the stop button it would have continues to cut into the part of the workpiece that I want to keep even though it was supposed to stop a mm short of the surface. (I’m planing off the plug side of a vcarve inlay.)

Is there anything in the file that is making this happen? Or has the Z-axis on my machine gone wonky? Haven’t had a chance to try a different bit yet.

I re-initialized the machine between attempts 3 and 4, same result.

241013 surfacing.c2d (284 KB)

2

Since your move to 6mm is OK, it would appear your CM setup is correct.

Is there any chance that the bit is pulling out of the collet? Over time a collet can wear out, and lose its gripping power.

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3

Can you post your gcode, or at least the first 30 lines or so?

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4

Ive had bits walk out due to dirty collets. I always blow them out with and air gun and once in a while they get a bath in acetone for good measure. Also clean the collet seat on the spindle with a rag and acetone. Seems to solve the problem

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5

I haven’t found the issue, but possibly some insight:

Your depth per pass is set to 0.381mm. The depth of the pocket is 3mm and the simulation preview shows 8 lines to get to the bottom.

3/8 = 0.375mm which is slightly off from your DOC (0.381)

8*0.381 = 3.048

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I’m not sure how DOC is handled in software when there is not enough stock left to do another full DOC, but obviously we end up at our desired depth. The simulation also doesn’t show any deviation in the rapids or toolpaths so this points to a mechanical issues as other have suggested. Certainly nothing I can see that points to a 3mm plunge.

Just to state the obvious, did you check your zero height? Your file posted here is fine.
but maybe it got switched → Just saw your 6mm test

6

If the last pass is less than the Depth per Pass, the remaining depth is used for Depth per Pass.

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7

So, after a night’s rest (and complete power down of all components) everything is back to normal today without touching the bit, the file cuts as it is supposed to. (as did the other things I worked on today)

I really don’t think the bit was slipping. The bits and collets are only a couple weeks old, I do clean them, and it would be really bizarre if it managed to slip exactly the same amount on only the first pass of four successive cuts. Plus, if it had slipped that much it would have been pretty obvious by the end.

Unexplainable weirdness I guess.