Configuration for the BitProbe V2 thickness

I don’t think this is quite the same question that has been covered by other threads, but it might be related.

I have a BitZero V2 probe on a Nomad 3. I put it on the top of the MDF board (which is flat and clean) and run the probing cycle. I rest my finger gently against the corner of the probe holding it onto the corner, because that appears to make X and Y probing more consistent. I let the probe cycle run.

Then I remove the probe and manually jog the probe pin to the surface, with a 0.05mm thick scrap of baking paper in between, I’m still at Z=+0.17mm when the paper grabs. It looks like there is a Z bias of 0.12mm. This is consistent between repeated experiments and also consistent with the error in depth I’m able to measure in machined pockets.

The zero reference surface is being estimated very slightly below where the actual surface is. This means that the software thinks the probe is very slightly thicker than it actually is.

I measure the thickness of the probe, ignoring the lip, as 13.10mm. It is consistent everywhere across the probe face.

Is there any way to see what Carbide Motion thinks the V2 probe thickness should be, and is there any way to tweek this value to remove the bias I’m measuring?

Nit picking would appear to be my special subject. I know I’m close to the machine resolution, but I’d still like to get the full accuracy the Nomad can provide.

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Please contact us at and we’ll work out how this should be handled.

My V2 probe does the same on my Nomad 883 Pro. For me, it’s not accurate enough for engraving purposes with respect to Z.

For Z on metals, I first do a Z-only probe with the BitZero, then turn the BitZero on its edge so it is in contact with the metal. Then I jog down until the endmill hits the metal stock, at which point the BitZero light turns on.

edit: The BitZero v2 measurement is always short by 0.175mm or just about, so using it as a probe first lets me get down to near the surface quickly to do the probe-light method.

Gerry, it sounds like the bias you are seeing is the opposite sense to mine. Just out of interest, could you measure the thickness of your V2 probe with calipers. Is it 13.10mm, the same as mine?

Hallo Mark,

I will do.

For clarity/review, my BitZero v2 always sets the zero to be around .175mm above the surface of the material.

Your zero is set below the surface?

Yes, below the surface.

When I try to manually jog to the surface it’s still 0.12mm when I hit. (Strictly, it is 0.17mm when I hit the 0.05mm paper).

So if your probe is 13.4mm thick, it will all make sense.

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Mine is 13.1mm at the thin part, but I was using the thicker part for the Z-only test, where it’s about 15.5mm or thereabouts.

I have a good quality imperial dial caliper and on that it shows the thick part to be 0.61" …

None of these measurements seem like ones people would pick for a design (the BitZero v1 was a nice 25mm), so I think it is supposed to be 0.6 of an inch but it isn’t.

Perhaps the plastic bottom, which is screwed on, might compress depending on how tight the screws are affixed, and therefore affect the accuracy?

The BitZero v1 was solid metal which I think is better in this regard but suffers from not being able to probe metal surfaces.

Well, there goes that theory. (BTW my V2 is 15.6mm high when including the lip, using a metric dial caliper)

The V2 probes are consistent with the lip 2.5mm high.

So if you are using this “thick mode” for the Z-only test, I would have expected your reference zero to be close to 2.5mm above actual surface, not just 0.175mm. Now I’m completely at a loss.

Pretty confusing - I’m not sure what’s going on either.

Perhaps it should be 1.524mm (0.6 of an inch) at the thickest part… though of course if yours is 15.6mm it would mean your probing would be too high like mine, no?

It’s a shame CM doesn’t let you specify the height of the probe - I can see why they don’t (to force people to buy their probe and not make one) but a small adjustment of a few mm would be great. It would let you put tape or something on the V1 to help it with metals.

The Z-only probe takes into account the 2.5mm lip since you are supposed to put the whole thing on top of the material for that probe.

Ah. I see.

I’ve only done the corner thing.

I thought of another approach to this measurement, so this morning I decided to repeat my tests.

I installed the original 1/2" MDF wasteboard on the base plate.

I used a corner probe cycle using the V2 probe, with a top surface 13.1mm above the MDF.

The probe cycle then parked the probe tip at (10, 10, 19), directly above where it just completed the Z part of the probe cycle. Now without changing anything else, I manually jog the probe down in 1mm steps to Z=14, and then in 0.025mm steps to the point where the contact LED turns on.

This SHOULD be at 13.1mm. Instead the contact LED turns on at 13.000mm, off again at 13.050mm. I can cycle between the two heights turning the LED on and off, so there is a little hysteresis there. The problem is that it should be at 13.1mm, not 13mm.

But the really interesting thing is that this time the virtual zero surface is now above the actual surface, not below as I was seeing before. I can check this. I take the probe out of the way and manually jog to (20,20,15) clear of the mounting hole in the SW corner. Then I jog down to (20,20,0).

This should be touching the surface of the MDF, but I can easily slip the 0.05mm paper under the probe tip. I jog down in 0.025mm step until the paper starts to grab at -0.175mm. That says the surface is 0.225mm below zero. This measurement is less accurate than the previous one because I’m looking at a local patch of MDF.

If I do the same thing starting at (30,30,15), the paper touch is at -0.275mm. I go back to (20,20,15) and paper grab is still at -0.175mm, back to (30,30,15), still at -0.275mm. (I’m doing the microjogging blind BTW, using the keyboard with my right hand but looking at the probe and wiggling the paper with my left. I only look at the Z position readout after I’ve decided where the paper is grabbing).

So, the MDF surface height can have at least 0.1mm ripple on it, based on a two spot test. This is not a great surprise, but it means that probing heights straight onto that surface is not going to be super accurate.

The probe flat body should kind of smooth this out, but in a biased way. It doesn’t sit on the average height but rather on the high points of the MDF. The test using the probe LED showed the probe top sitting 0.1mm below the expected height, but the MDF spot checks were 0.175 or 0.275 below the expected position. I believe the probe is sitting on the high spots of the edge of the MDF, where it has slightly swollen due to humidity.

I suspect that my initial results (when I started this thread) were biased the other way because my MDF was more distorted than I thought it was.

Result One: don’t try precision measurements based on MDF

Next I removed the MDF and put the probe directly onto the corner of the base plate and probed the corner. Repeating the height measure of the probe I still see two click (0.05mm) hysteresis centred on 13.00mm (12.975 to 13.025). Doing the paper test at (20,20) it grabs at -0.05mm, so the plate surface is at Z=-0.1mm. This is consistent with the bias on the LED probe top surface.

Result Two:

Now I think that internally, the CM probing process assumes that the V2 probe is 13mm thick, where as it is actually 13.1mm thick. This puts the reference zero surface 0.1mm above the actual surface the probe was sitting on. When we then manually jog to the probe surface we touch it 13.0 mm above the reference surface. Or if we manually jog to the base plate surface we find it 0.1mm below that reference. ie

------ top of probe


------ virtual zero
------ actual base plate surface

I hope this shines some light on the whole Z probing issue that seems to appear in different forms in different threads. I’d be interested to see if others can repeat the V2 probe to base plate measurements and verify Result Two.


Result Three,
The Z-only probing assumes the probe is 15.5 +/- 0.025 high. It’s actually 15.6mm, so there is still a 0.1mm bias using Z only probing.


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