Losing zero point when changing bits

I’ve been experiencing losing my zero point when changing bits. When I’m doing layered text projects that are detailed and have 3 tool bit changes in one layer going from 1/4" to 1/8th" then finishing with a 1/16th" for fine detail, I find that the 1/16th" usually ends up being out of register or off center. Your advise or observations would be greatly appreciated.


Brian, what are you doing to set your XY zero at the start of the job?

What are you doing to set your Z zero at the start of the job and after every bit change?

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If just the X or Y are out, perhaps one or more of the machine’s axis are slipping a little during the other operations, in which case you might need to slow things down a little for those toolpaths or inspect your machine for mechanical soundness.

Or maybe the X&Y zero was never correct (maybe because your endmills are not exactly 1/4" or 1/8") and the error only really manifests when you get very small. You could try setting the zero with the tiny endmill instead.

I’m using the bitsetter for Z zero after every tool change.


Will do Gerry…thank you!



Is this a new problem… has this happened before on other projects?
Were you seeing this flaw in the simulation?

I ask this because I had a similar problem… I found that it was in the way I was designing.

the machine was following the toolpahts that I gave it.
in the simulation Id have other marks digging into my other layers. That was until I went to using the same line to create a new tool path.

before… I was layering new lines into of my old ones to make new tool-pahts from… I found this to be a No-No

When you are probing, are you using the “pins” or the bit?

If you are using the bit the possibility exists that the flute is causing a small amount of error.

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Any chance you are moving the router when changing bits? It won’t move easily, but it can move.

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Thanks David for your reply…
After all the great suggestions and input from fellow cnc’ers on the subject, I believe my problem was exactly what you mentioned. I normally tighten my bits in the collet pretty tight. When I go to change them I do make a noticable movement on the router. So between that and using a much smaller bit size to set X,Y,Z position when starting a project, the problem of keeping a zero point has been all but eliminated.
Thanks so much for the input…I’m always learning.


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