Vee bit probe over run after zero

Yesterday I was installing my first vee bit on my Shapeoko XXL and had a bit of trouble. The project was already centered on X, Y since I had been using an end mill. So I installed my Vee bit, set the Z zero with BitZero, and went to work. Unfortunately, it went right through my 1/16 material. I verified my setting and re-zeroed with the BitZero with the same results. Next, I sent the bit to 0 XYZ. I found that the Z zero was about 1/16 lower than the surface I used the Bitzero on. I reset the Z zero by eye and had great results. This has me confused because I have used the Bitzero for the past week with end mils and have had great results. So I don’t understand why the Vee would not offer the same consistency. Any help or suggestions is appreciated! Thank you.

Hi @bojamesaei,

Any chance that when you zeroed Z only you might have had the BitZero overhanging the corner of the stock?
1/16" error sounds suspiciously close to the height of the BitZero lip. When zeroing Z only, the BitZero must be laid on the top of the stock


I see what you are saying but in that case the Z should have been zeroed higher than the stock, correct? If the BitZero is high the zero should be high the way I see it.

Yes. Was the Probe on top of your work?
If you’re zeroing Z-only, you want the whole probe on top of the stock. If it’s overhanging the corner, zero will be lower.

Nope, it’s a bit confusing but see it this way: The probing looks for the absolute Z value where the bit contacts the probe. Then, Carbide motion subtracts the height of the probe, to figure out where the Z of the stock surface is.

  • when the probe is used for XYZ probing, it is overhanging the corner, hence the distance to subtract is less that the probe height, it’s the probe height minus the lip height
  • when the probe is used for Z proving, it must be installed entirely on top, because CM expects it and will subtract the full height of the probe.

If you put the probe on the corner, overhanging, and probe Z only, your bit will alreayd be lower than where CM thinks it is, it will subtract a full probe height, ending up 2mm deep into the material


So when zeroing only Z you do not hang the lip off the edge? Sounds like I missed a step.


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Yes. CM has hints for how to position the probe (ignore the red part):


Got ya! Thank you two! That makes more sense so that you can zero the Z from anywhere on the work surface. Looks like we have a classics case of not following directions. Thank for the help! I’ll got try it now.


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