Probe Feature
Before probing make sure the probe circuit is working. Send the ? character from a serial terminal to get the current status. If your gcode sender does not show you the raw status response, you may need to use a simple serial terminal. The status response will show you any active inputs like the probe.
It will look something like this with no switches active...
<Idle|MPos:0.000,0.000,0.000|FS:0,0|WCO:0.000,0.000,0.000>
and something like this with the probe switch active...
<Idle|MPos:0.000,0.000,0.000|FS:0,0|Pn:P|Ov:100,100,100>
The Pn: section is for active input pins and the P indicates the probe is active.
You do not want to see the probe active when it is not touching and see it active when it is touching.
Use the $6 or $Probe/Invert setting to flip the logic if your is reporting backwards.
Here is a typical gcode sequence for a Z probe. There are other ways, but this one I feel is the most accurate. Many senders have this feature built in, including the WebUI, the question gets asked a lot.
Typically it is done in the Z direction, but any direction could be specified.
- Send...G38.2 Z-5.0 F50 This tells Grbl to probe a maximum Z distance of -5mm at a speed of 50mm/min
- Receive...[PRB: 0.000, 0.000, -15.621] This is a typical response after touching the plate. This was the machine space location when it touched. The current location is probably a tiny bit lower due to the deceleration.
- Send...G53 G0 Z-15.621 This tells Grbl to move to the actual probe location in machine space. This corrects for the overshoot.
- Send...G10 L20 P0 Z3.00 This tells Grbl to zero the current work coordinate system (P0) to the thickness of your touch plate (3.00mm).