Failed touch probe

Can someone tell me why when I have a failed touch probe operation (like forgot to attach clip to bit or or was too far away) I have to start all over and reinitialize my xxl? Why can’t a failed probe attempt just fail and let me try again? Very frustrating. I’m on latest versions of both products.

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I absolutely agree. I would love to have an additional button that reads:
“I started probing too high, everything is fine.”

I was carving a box top about 2 hours ago and I set the X & Y manually on the center of the project and then used the touch probe to set Zero. I set the bit too far above the touch probe and it failed and made me reinitialize the machine. I did not think it too big of a deal but since the probe had not set any thing why not let you re-probe instead of initialize?

In the first case, @bennesh1 & @MadHatter the machine doesn’t know if it lost steps due to the bit hitting the probe without properly ending the cycle.

In the second case, @gdon_2003, the software should know that it simply timed out instead of bottomed out, but programmers will be programmers.

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How would it know that in the case of a malfunctioning probe?
This the behavior of the machine control software, GRBL. It’s not handled by Carbide Motion.


Hmmmm … are you saying that CM is not in control of the probe zero function? I thought gcode was generated to perform this function.

What is the GRBL command to start a zero probing function?

The command is G38.2 as in:

G38.2 Z-26 F100

which translates to:

  • G38.2 — probe command
  • Z — along the Z axis
  • -26 — down 26 units in the current measurement system
  • F100 — at a speed rate of 100 units per min. in current measurement system

Carbide Motion sends the probe command and waits for a response from Grbl — in the absence of a hard real-time OS, we have to yield control to Grbl.

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CM generates the probe gcode and sends the gcode, but grbl does the interpretation and controls the machine behavior.

I understand (from the being safe and preventing damage to the machine aspect) the idea of homing when the probing cycle fails, I just wish that I could have an option to not go through a full homing and bit-setting cycle when I set my bit too high before beginning a Z-probe.

I would like the ability to tell the software “No, something is not wrong with the machine - this error was an organic error - please continue.”

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Allowing homing mid-state also potentially confuses the internal program state — I think I’ve found a bug where dimensions will be off after doing a manual homing — which in retrospect, was a stupid thing to do (fortunately, it was cheap stock) — and if the bug is accepted, I’m sure it’ll be low priority.

So, grbl returns an unknown error code for CM to operate on?

No, grbl returns a probe error AND enters an alarm state. The only way to recover from that is to home or unlock.
So, I suppose CM could allow the user to make that decision. I’m not sure if grbl actually loses track of position in that alarm stop, though. For example, let’s say your probing is set to probe down for a max of 25mm and you don’t reach your probe because it’s 28mm away. I don’t know if grbl decelerates to -25mm or just gets to -25mm, throws its hands up, and goes into alarm without further tracking of movement.

There’s also the G38.3 probe which just won’t error at all.

I think CM is doing what’s safest for the machine. With the new Z and the HDZ, one can definitely do some damage on a bad probe.


Thank you for the explanation, @neilferreri. I know this has gotten down into the weeds, but it is at least educational to know the details. (I’ve done a bit of and am now piddling with some programming, thus my interest in the “weeds.” :smiley: )

It is frustrating at times to have to do a dance while someone else is choosing the music. :smiley:

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So the moral of the story is to have your probe and bit properly placed and you wont need to go through the alarm state and reinitialize to recover. I had stated earlier that I was probing for Z but since I got the bit setter I do not use the touch probe too much and I just forgot about the distance that the bit must be above the probe. There have been tremendous changes in CC and CM. Getting used to the changes has been problematic for me. You get used to working one way and then you are up ended. I am not complaining about the changes because they have all been good but we are creatures of habit and changes in habit are disconcerting.

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