Z-axis slippage

I have been trying to engrave the top of a small ring box for my granddaughter and the engraving gets less deep as the machine moves forward on the piece. The toolpath is cutting left and right and working it’s way down the piece. As it gets over halfway the engraving is noticeably less deep. The wood is not terribly hard. To insure the wood had a flat surface I did a light surfacing cut with a 1/4" end mill and can see the z-axis is getting less deep. 2 photos attached if I can. I have tightened the drive belt about as much as I dare, Checked the drive pully setscrews for tightness and that they are on the flat spot of the shaft. Have the cullet very tight. Looking for ideas on what to check next.

Hi Dave,
Check that your collet, nut, and the inside taper of the router are clean and free of saw dust. A little debris in there can prevent a “tight” collet from getting a good grip on the shaft. You can also measure the stick out before and after a cut to see if there was any slippage.


Depending on you Z axis, a belt z might be loosing position but they usually cut deeper. A Z-Plus and HDZ are not likely to slip. The next issue might be as Lester suggested your bit is slipping and moving up as the cut progresses. Be sure to check all your mechanicals like v-wheels are tight and your stepper motor screws are tight with one set screw on the flats.

Thanks for the reply. OK, I removed the collet and made sure all the dust in the collet and nut was gone. Did another test and the surface cut looked good, but the engraving still got light in the bottom 1/3. I realize now I did not clean up in the router when I had the collet out so will give that another go tomorrow. I could also get a new collet and see if that helps. Don’t have one on hand to try so that will take a couple days. Is there a specific source for the collet you can suggest? I am pretty sure I got this one from carbide.

OK, after trying the suggestions and searching around I decided to upgrade to the z-plus axis. Have ordered that today so will see if that fixes this problem too.

I started out with the belted Z-carriage and eventually upgraded to the HDZ (the Z-plus was announced but sold out at the time). The upgrade from the belt drive Z is well worth it as they aren’t susceptible to belt stretch.

Did you check your v-wheels and pulley set screws?

Depending on your router/spindle, you can find precision collets from C3D for their router or the Makita trim router. Elaire Corporation also sells a variety of them too.

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Thanks for the reply Brian. Glad to hear what you said about z-carriage. I thought even if it doesn’t fix my immediate issue it is a good upgrade for my machine.

Yes, I checked the pully and set screws and the v-wheels. The lower right hand v-wheel has a tiny bit of slack in it and tomorrow I will see if I can snug it up.

I have the C3D compact router and I am already using their “precision collet”. The ones from Elaire look like the identical style.

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