Warning about going below zero

Today I got the warning about the machine going below zero by 1.4mm. I canceled and then checked everything, Z was exactly where it needed to be and all my measurements and top of material were as expected.

I had the probing pin in though, not the first bit. So I used the Load new Tool option and actually put the first bit in. It measured on the bitsetter and then I moved the bit to the material (actually slightly in front of) and lowered to Z. It was perfect.

I reloaded my program and did not get the error. So I assume it was using the shorter length of the probing pin and thinking that it would have to go below the machine Z capability to get to Z zero on the job.

Maybe the measurement for that warning should not be calculated until after you have put the first real bit into the collet after starting the job. I don’t usually load the bit until after starting the job.

Wording might be misleading, but it doesn’t mean it’s going below zero, it means it’s going below the bottom of the Z travel. Note: if you’re zeroing on the top of the workpiece, all cutting moves are below zero (i.e. -Z).

But you are correct, if the probe pin is shorter than the tools used for the job, and the probe won’t reach the lowest spot in your toolpath, it should issue this warning.

it knows where machine zero is (upper right rear corner). And it knows where it is in machine coordinates when you zero your part. If the current Z position minus the lowest Z in your path are lower than the machine envelope (stored in CM & GRBL), then it issues the warning.

The machine (or CM) doesn’t know if you are using the first tool or the probe pin.
If you are not using the bitsetter, (I don’t), there are no other toolchanges to trigger the bounds check.

It’s a limitation of only having one tool offset register. On commercial machines, you set all of the tool length offsets, then set the workpiece zero, then load the toolpath & it can calculate each path with the correct tool & tool length offset. It then doesn’t need to consider the probe since it isn’t used in the toolpath.

In summary, the warning doesn’t mean you will crash into the table, it means the Z axis doesn’t have enough travel to get to the lowest Z in your path.

Screenshot 2023-11-07 161825

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Agreed. Maybe said something wrong in my description. But if the warning were “true” then it would bottom out Z and lose steps which would mess the project up.

Maybe the wording could be changed to include “using the current bit” to be a little less confusing. Then people that intended to change the bit would see it but realize that it was not relevant if they planned to change.