Z probe fails - BL Touch - print continues

  • I’m hoping I have answered my own questions below but have a long print running so can’t test for some time.

    I have just begun to get occasional cases of a report of ”Z probe failed” during homing.
    This typically happens when the z axis is quite high at the start and is reported well before it gets close to the bed.
    I suspect electrical noise from the hotend fan and/or heatbed as I don’t recall seeing it on a cold start print. My hotend fan automatically runs if hotend > 40C
    I moved bed heating to after homing with no effect.
    I’ll try disabling the hotend fan as well, just concerned about heat creep jams if I do.

    Do others report same thing?
    Not sure why it’s only just started happening.

    My main question though is why does the print continue in mid air after this reported failure?

    Could it be because in my start G code I have an M92 Z0 then G1 Z5 to ensure the BL Touch has enough height before homing?

    I.e does calling G28 clear the previous home position and put all axis in an unhomed state when called ?

    Or would the correct procedure be to use M564 S0 H0 before lifting the head and then resetting it to M564 S1 H0 before homing.

  • Moderator

    G28 will set everything to unhomed, but If you're using G92 Z0 in homeall.g, you're basically telling it the z axis is homed and at 0.

    Usually the head would be lifted with G1 S2 Z5 which would allow movement without being homed for that move only. Then XY home, and then move to bed center for G30 probe.

    Please post your config and homing files.

  • @owend
    Edit: Should read G92, not M92

  • Moderator

    Right. i got your meaning.

  • Actually just noticed that I had commented out the G92 in the start G code as I had put the lifting code in homeall.g

    The contents of that is below and uses the G1 S2 method you mention.

    Print is finished now, so trying to reproduce.
    Of course it's not doing it 😡

    ; homeall.g
    ; called to home all axes
    ; generated by RepRapFirmware Configuration Tool v2 on Sun Jan 06 2019 15:30:47 GMT+1000 (Australian Eastern Standard Time)
    G91                     ; relative positioning
    M280 P3 S160 I1		; Alarm Release and Push-Pin UP
    G1 S2 Z10 F6000           ; lift Z relative to current position
    G1 S1 X-210 Y-210 F1800 ; move quickly to X and Y axis endstops and stop there (first pass)
    G1 X5 Y5 F6000          ; go back a few mm
    G1 S1 X-210 Y-210 F360  ; move slowly to X and Y axis endstops once more (second pass)
    G90                     ; absolute positioning
    G1 X90 Y95 F6000         ; go to first bed probe point and home Z
    M558 A1 F300			; Set single probing at faster feed rate
    M98 Pdeployprobe.g      ; deploy mechanical Z probe
    G30                     ; home Z by probing the bed
    M558 A5 S0.03 F60			; Set multiple probing at slower feed rate
    ; Uncomment the following lines to lift Z after probing
    G91                    ; relative positioning
    G1 S2 Z5 F100          ; lift Z relative to current position
    G90                    ; absolute positioning
    M98 Pretractprobe.g     ; retract mechanical Z probe

  • Moderator

    @owend said in Z probe fails - BL Touch - print continues:

    M98 Pdeployprobe.g ; deploy mechanical Z probe
    M98 Pretractprobe.g ; retract mechanical Z probe

    This isn't necessary for the BLtouch when using M558 P9 probe type and firmware 2.0 or later. The Duet will keep track of the deployed state of the probe and manage it as needed during probing.

    Everything else looks good.

Log in to reply