BitZero V2 precision

CNC Machines Nomad
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What is the expected accuracy of the BitZero V2? (used with a Nomad, with the probing tool)

I started wondering, because my Nomad consistently cuts slightly into the wasteboard after setting the Z zero using the probe. Not by much, and this isn’t in itself a serious problem, but this got me thinking about what I can actually expect from the probe. The accuracy gets much more important when I intend to cut something in an existing design, rather than from raw stock.

Also, is there a way to calibrate the probe?

For all probing (especially) I’m always holding it with my hand, pressing so that it doesn’t move.

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In general you can calibrate a Z probe like this:

  1. Face a piece of stock with an endmill, you now know that the endmill is precisely 0mm away from this face.
  2. Probe the stock.
  3. The height at which the probe triggers above the stock is the exact height of the probe.
  4. Optionally, repeat steps 2 and 3 and average the result (and also get an idea of repeatability).
  5. Store the measured height offset.

However I’m not sure whether Carbide 3D offers the ability to use a custom offset. You could almost certainly do it manually in G-Code, something like this:

; First:
; - Face stock
; - Manually move endmill within 10mm of stock

; Probe at most 10mm with a feedrate of 100mm/min
G91 G38.2 Z-10 F100
; Set the reached point as <height of stock> above zero. 
G92 Z<probe height>
; Retract
G91 G0 Z10

Other G-Code senders can handle it too. @neilferreri wrote this for cncjs.

Regarding the accuracy of the BitZero specifically, Carbide 3D is generally pretty sparse on specs, so I wouldn’t expect a whole lot from it. If you want precision, I’d buy something else that specifies it. Personally, I like this one which is specified to 10µm but mine seems closer to 5µm.

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The first place to check is the actual thickness of the stock. That is the issue most of the time in situations like what you’re describing. That is the single pitfall of using the top of stock… final thickness or any thru cuts being too high or low.

If final thickness or thru cut depth is the main objective, then I would suggest using the bottom of stock. With the V2 I probe Z only on the wasteboard or fixture plate. Then I’ll put the stock in and probe XY.

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In all jobs where I intend to cut through the stock, I set my Z zero to the wasteboard, not the stock top.

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Perhaps the wasteboard isn’t flat?

Given that you describe it going slightly into the wasteboard, and that when you are cutting through the stock you set the zero to the wasteboard, the implication is that you are putting the BitZero onto the wasteboard… if I understand correctly, that is.

After zeroing, do you attach your stock? Or do you zero to a part of the wasteboard that doesn’t have any stock on it?

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