BLTouch P9 mode retracts the probe to late ?

  • I am using a BLTouch. This z-probe is mounted onto my main X-carriage. The offset between the z-probe and the two nozzles (left and right of the z-probe, magnetic pickup system) is more (negative) than the offset normally used by the BLTouch 8.3mm (not the trigger height), I use -6.0 here as trigger height:

    M558 P9 H8 F100 T1000; Set Z Probe to type bltouch
    G31 P25 X0 Y0 Z-6.00 ; Set Z probe trigger value, offset and trigger height - bltouch

    I put the hotends in parking position (left & right of the bed) when z-probing to be able to probe the bed without crashing the nozzles into it.

    When running the "Run Mesh Grid Compensation" it does this at the moment:

    • Move to first x/y probe point and z height (z=8)
    • Deploys probe
    • Moves downward until probe triggers (probe stays automatically retracted by the bltouch for around 1sec.
    • Moves upward while the probe stays in retracted state for the 1sec mentioned above
    • During upward move the probe gets deployed again (1sec is reached)
    • Probe reaches z=8 again
    • Probe gets retracted again
    • Now it continues the procedure by moving to the next x/y position to probe

    What I expected it to do:

    • all the steps above but: retract the probe right after the probe got triggered (automatically retracted by the bltouch on probe contact)
    • beeing able to define the z probe z-starting position independently of the dive height, no need to raise it to z=8mm all the time, but I need it to travel down that far to be triggered.

    I know I should be able to fix this by printing a new BLTouch holder so it is at its z offset from the nozzle to the bltouch casing where it should be: 8,3mm and defining the nozzles z-offset (tool definitions) from this z-point.
    But this isn't fixing the retract timing issue, the retraction command is currently run after moving back to the z-height, where it should be run directly after the probe was triggered.

    My current tool definitions:
    G10 P0 X-35.9 Y9.80 Z-1.3 ; Set tool 0 axis offsets - e3d
    G10 P1 X37.0 Y9.00 Z0 ; Set tool 1 axis offsets - e3d clone

    I am running Firmware 2.0RC6

    Okay, mounting the BLTouch to the position where it should be and you won't notice the retraction problem as the z position is reached before the bltouchs internal 1sec redeploy timer.
    New config:
    M558 P9 H2 F100 T1000; Set Z Probe to type bltouch
    G31 P25 X0 Y0 Z1.00 ; Set Z probe trigger value, offset and trigger height - bltouch - bowden
    G10 P0 X-35.9 Y9.80 Z-2.35 ; Set tool 0 axis offsets - e3d
    G10 P1 X37.0 Y9.00 Z-1.25 ; Set tool 1 axis offsets - e3d clone

    Sorry for the long post

  • administrators

    I am fairly sure that retractprobe.g is run as soon as the trigger is registered; but I'll check tomorrow.

    I am aware that the bltouch deploys and retracts twice instead of once per probe point. On the work list for firmware 2.01 is an extra parameter to the M280 command, which I hope will resolve this issue.

  • administrators

    I have confirmed that the code starts running the retractprobe.g file as soon as the probe has been triggered, concurrently with starting the move to raise the probe. But I am also aware that several users have observed the probe re-deploying and re-retracting. Investigating this is on the work list for firmware 2.01. I already have a theory about why this is happening.

  • Thank you for investigating this.
    I don't use the bltouch anymore so I can't give a fast feedback if you have found a fix.
    I can mount the bltouch again for testing it, but that may take a few days then.

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