Issue/question on cartesian G29

DaveA

I recently updated my old FolgerTech i3-2020 from Marlin to a Maestro and things were going very well. It was setup with a BLTouch probe and I could generate a reasonable bed heightmaps.
Today I updated to a E3dV6 hot end in which I moved the probe from the left side of the nozzle to the right. The only change I made was to the config to change the x offset of the probe.

; Z-Probe
M574 Z1 S2 ; Set Z endstop controlled by probe
M558 P9 H12 F600 T6000 ; Set Z probe type to BLtouch and the dive height + speeds
;G31 P500 X-34 Y0 Z2.80 ; Set Z probe trigger value, offset and trigger height
G31 P500 X29.5 Y0 Z2.80 ; Set Z probe trigger value, offset and trigger height
M557 X0:200 Y00:200 S20 ; Define mesh grid

Now when I do a G29 it starts probing the bed but generates several warnings such as:

2/9/2019, 7:41:04 PM Warning: Skipping grid point (20.0, 180.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 180.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 200.0) because Z probe cannot reach it
Warning: Skipping grid point (20.0, 200.0) because Z probe cannot reach it
2/9/2019, 7:40:16 PM Warning: Skipping grid point (20.0, 140.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 140.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 160.0) because Z probe cannot reach it
Warning: Skipping grid point (20.0, 160.0) because Z probe cannot reach it
2/9/2019, 7:39:28 PM Warning: Skipping grid point (20.0, 100.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 100.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 120.0) because Z probe cannot reach it
Warning: Skipping grid point (20.0, 120.0) because Z probe cannot reach it
2/9/2019, 7:38:40 PM Warning: Skipping grid point (20.0, 60.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 60.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 80.0) because Z probe cannot reach it
Warning: Skipping grid point (20.0, 80.0) because Z probe cannot reach it
2/9/2019, 7:37:52 PM Warning: Skipping grid point (20.0, 20.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 20.0) because Z probe cannot reach it
Warning: Skipping grid point (0.0, 40.0) because Z probe cannot reach it
Warning: Skipping grid point (20.0, 40.0) because Z probe cannot reach it

I'm assuming that the coordinates shown are X and Y position on the bed. I can G1 over to all these points and do a G30 with no problem so I'm not sure what "probe cannot reach it" is trying to tell me.

Any ideas?

aidar

This means exactly what it says - probe cannot reach it. Yes you probably can G1 over these points, but this is with nozzle, not with probe. As you probe x is 29.5 and you want to probe at x0, that means your x axis minimum limit should be at least -29.5 . So do some math and adjust your M557 values.

DaveA

Thanks, I can do that. I thought I read that the firmware would handle it and would position the probe accordingly. Why tell it the offset of the probe from the nozzle?

aidar

@davea said in Issue/question on cartesian G29:

Why tell it the offset of the probe from the nozzle?

Because let say you want to probe at X10 Y10. Firmware knows (after homing of course) where your nozzle is, but it does not know where you probe is if you dont tell it probe offset.
You can always define your probe offset as X0 Y0, but then actual probing point will be offset from point you want to probe by physical probe offset parameters.
I hope this make sense.