Incorrect cut depth

Machine is cutting .1" deeper than it should. Zero height is set to stock bottom. Stock is 1.5" thick. I even surfaced in .005" increments, 3 passes on each side (was 1.53" thick). Project is two clam shell boxes cut out of the same board. After the 4 pockets were cut I measured them all at 1.1" deep, should have been 1". Then the male/female lip was .6" deep, should have been .5". I figured “At least it’s symmetrical” and let the machine continue to run. Problem occurred when the cut out for the first box was being finished. I had a rough cut (with tabs), then a finish cut (also with tabs). It didn’t occur to me that the +.1" on each cut was leaving only .02" on my tabs, so on the finishing pass things went south. Whole box broke free from its tabs and jammed up the works. DOH! Took the stock off the spoil board and put it the fire wood bin, and then I noticed deep cuts in the spoil board, about .1" according to my calipers.

I’m wondering if my bit setter is wonky. As the bit descends on the bit setter button, it hits the button and button moves down slightly (maybe .1"?) before the green light comes on. Additionally, when you look at the machining marks on the rough cuts the first pass is twice and deep as the following cuts. Its as if the machine thinks the bit is shorter than it actually is.

CCP file:
Bowl 03.c2d (516 KB)

Let me know what I’m missing here, and as always, I really appreciate the help from y’all.


Any chance your bit pulled out of the collet just a touch, like maybe .100". Sometimes those deep contour cuts will do that to a bit. If your bit is still in the spindle / router you can verify that by rechecking where Z zero is. If it’s .100" off, that’s what happened.


Whelp. That was it. Z was off by exactly .1". I feel a bit silly. I really thought I gave it the beans when I tightened it. So many lessons to learn…

Thanks @Ed.E


I have been busy at work and went out to mountains for a few days so haven’t had time to contemplate this more.

As I start to wrap my head around it more I have some thoughts.

That collet was VERY tight. In fact, before I started the cut I was fussing around with bit length and sweepy options and forgot to tighten the collet more than hand tight. When it started cutting there was clearly something wrong. Hit the stop button and quickly realized my mistake. Re-set everything, inspected everything, and really gave the collet a good tightening. The bit must have slipped in the first pocket cut because every cut was the same .1" too deep. Is a DOC of .1" too much for a 1/4" bit? Also, I noticed when inspecting the collet after the “incident” that there was some oil on it. Didn’t occur to me at the time but I’m guessing they oil them from the factory and that should be cleaned off before use?

Thanks again!

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