Auto Zero Touch Plate and Z Height

Hi, everyone.

I’m tagging @_Michael and @NeilFerreri, and @gwilki because, well, frankly, I’m a total newb both to this forum and CNC in general. @_Michael has given me excellent guidance in the past, and now I’m back for more.

Here’s the issue I’m having: Recently, I’ve noticed that when I use the Auto Zero Touch Plate it is deadly accurate (in terms of outcome) on the XY. But whenever I run the probe, the Z ends up about a millimeter above the surface of the blank. Is this some kind of offset thing? I’ve been doing a lot of “test dummy” carves lately, in advance of actually figuring out what the heck I’m doing, and I’m missing something in terms of the logic of the Z height. I understand the concept of a retract height for rapids, but I don’t know why the Auto Zero Touch Plate is giving me that Z position when I probe.

Any insights?

PS, I’m using Rhino 7 for the 3D modeling and MeshCAM for the CAM stuff and gSender for the g-code.

I don’t have an Auto Zero Touch Plate, but I believe when the probing sequence is done it intentionally moves to X0 Y0 Z1. You wouldn’t want it going to Z0 and potentially touching the surface of your stock.



Yeah, that makes sense, and I didn’t have problems with it before I noticed it and started monkeying around with it. For example, on my latest “test dummy” bass body carve, I used the probe to get the XYZ and didn’t monkey with the Z height at all, and the neck and pickup pockets were dead on.

I think I know what I’m doing wrong. Let me know if this makes sense. When you use the Auto Zero Touch Plate to get XYZ, it’s going to record the exact machine coordinates relative to the blank. What I usually do at this point is set those machine coordinates for XY to 0, so I can return to the exact same spot without having to re-probe. I probably screwed up not understanding why the probe moves the Z to Z1, so if I set that Z1 to Z0, I’m guessing my carve is going to end up a millimeter short in terms of total depth of carve? Because now I’ve told the machine that Z1 is actually Z0. I think I’ve managed to mess up in the other direction as well, so that the carve is slightly too deep.

That’s what the probe does though…it sets your work zeroes.
Are you changing your work zero and trying to go back later on?

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So, like if I’m going to be doing a rough pass then a finish pass, I use the touch plate to get the XYZ coordinates of the blank. Then, I use the “Set to” button for the XY, so that if I need to hit the “Go to XY Zero” button, it will return to the “relative” coordinates of the blank. So, I’m relying on the probe for a consistent and repeatable XY, and that has gone great. But I think I’ve misunderstood the fundamental thing you mentioned: The probe sets the Z a millimeter above the blank, just to be safe. And I’ve been messing around with that setting instead of trusting it. So, generally, no. I don’t change the work zero (thanks for that term, by the way; it captures it). But like a dolt I started messing with the Z, and that’s where everything has been going wrong in my carves.

The second part of this where you use the “Set to” button is not needed and possibly detrimental. The probe sequence already does the “Set to” part for each axis that was part of the probe sequence. Also it doesn’t really matter where the bit is located at when it finishes the probe sequence. What does matter is where the zero’s are.

To confirm that the probe is setting the zero’s correctly I would run the probe sequence then remove the probe from the area. Then jog the bit just off the work in XY and hit the “Go Z” button. The end of the bit should be at the same height as the stock. Then you can raise the Z 1mm and hit “Go XY” and the bit should be in the correct XY position. When everything is working right you can just “Go to” for each axis but I suggested moving off the work before checking Z in case something is wrong and it goes too low.

One more thing is that if you are using multiple bits on a job is that you only need to probe Z after the first bit, assuming you use the same start position for all jobs. The X and Y stay the same and you just probe Z for the new bit.

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To clarify and verify everything said so far - the probe routine already sets the zeroes. The movement at the end (and this is consistent across both AutoZero and standard touchplate) goes to XY 0 and Z (some value) which is above the workpiece to prevent dragging/issues. For Autozero, it’s 1mm, for standard, it’s a bit more than that. There is no need to set any more zeroes on any axis.

If you want to verify the height, use the Go To Z 0 button - as Michael mentioned it should be just touching the workpiece.

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Thanks, everyone! I think that solves my issue and I’ll use your advice for the next carve!

@The_Unknown_Bassist As your issue is resolved, I’ll close the topic.