zprobing followed by printing crashes bed



  • I am having a lot of difficulty with zprobing followed by printing.

    bottom line - when printing, the head crashes into bed by a mm or so (enough to gouge aluminum bed and rip 3m tape but still tries to print)

    where am I going wrong ?
    Is this probing saved somehow ?
    Does Reboot lose probing info.

    Pics available if needed

    Many Thanks

    Pete

    Info

    I have a homemade delta with a duet wifi.
    400mm H x 220mm x 220mm.
    Very solid construction (all aluminum 40x20 - no play in carriages / hotend)
    DuetEthernetFirmware-1.18.1stable
    DuetWifiFirmware-1.18.1stable
    JohnSL type probe connected to probe connector

    I calibrate the zprobe per Calibrate the Z probe trigger height.
    I zero out Z in G31 in the config.g
    jog the head to touch a piece of paper (this is at 0.1mm z height)
    send a G92 Z0
    Head up 10mm
    send G30 S-1 multiple times
    This results in a g31 value -0.451 consistently
    I then put this value into config.g like so
    G31 X0 Y0 Z-0.451 P250 ; set the zprobe height and threshold

    Then I run G29
    145 points probed

    then I send a M500

    Then I try printing and the head crashes the bed
    (i guess by about a mm)
    primary layer height 0.2500mm
    first layer height 59%

    here are what i think are the relevant bits of my files

    config.g
    ;*** Machine Specifics
    M665 R220.1 ; delta radius
    M665 L454.2 ; diagonal rod length
    M665 B205 ; printable radius
    M665 H402 ; homed height
    M666 X0 Y0 Z0 ; endstop adjustments

    ;*** Z Probe and Compensation
    M557 R135 S20 ; define mesh grid
    M558 I1 P5 X0 Y0 Z0 H6 ; a switch not used for homing (johnsl three-pin to zprobe connector)
    G31 X0 Y0 Z-0.451 P250 ; set the zprobe height and threshold

    M208 S1 Z-4.0 ; minimum z
    M501

    from config.g.bak
    ;*** Machine Specifics
    M665 R220.1 ; delta radius
    M665 L454.2 ; diagonal rod length
    M665 B205 ; printable radius
    M665 H402 ; homed height

    ;*** Z Probe and Compensation
    M557 R135 S20 ; define mesh grid
    M558 I1 P5 X0 Y0 Z0 H6 ; a switch not used for homing (johnsl three-pin to zprobe connector)
    G31 X0 Y0 Z0 P250 ; set the zprobe height and threshold

    M208 S1 Z-4.0 ; minimum z
    M501

    from bed.g

    ; Auto Calibration For Delta Printer

    M561 ; clear bed transform
    G31 X0 Y0 ; don't want probe offset
    G28 ; home printer
    M104 S210 T0
    M109 S210 T0
    G4 S5

    ; 13 points, 6 factors, probing radius: 177, probe offset (0, 0)
    G28
    G30 P0 X0.00 Y177.00 Z-99999 H0
    G30 P1 X113.77 Y135.59 Z-99999 H0
    G30 P2 X174.31 Y30.74 Z-99999 H0
    G30 P3 X153.29 Y-88.50 Z-99999 H0
    G30 P4 X60.54 Y-166.33 Z-99999 H0
    G30 P5 X-60.54 Y-166.33 Z-99999 H0
    G30 P6 X-153.29 Y-88.50 Z-99999 H0
    G30 P7 X-174.31 Y30.74 Z-99999 H0
    G30 P8 X-113.77 Y135.59 Z-99999 H0
    G30 P9 X0.00 Y88.50 Z-99999 H0
    G30 P10 X76.64 Y-44.25 Z-99999 H0
    G30 P11 X-76.64 Y-44.25 Z-99999 H0
    G30 P12 X0 Y0 Z-99999 S6

    G1 X0 Y0 Z100 F15000 ; move head up to 100

    from the start of my Simplify3d sliced calibration xyz cube
    ; G-Code generated by Simplify3D(R) Version 4.0.1
    ; Aug 10, 2018 at 5:49:26 PM

    G90
    M82
    M106 S0
    M140 S60
    M190 S60
    M104 S190 T0
    M109 S190 T0
    G28 ; home all axes
    G92 E0
    G1 E-1.0000 F1800
    G1 Z0.147 F1000
    ; process Process1
    ; layer 1, Z = 0.148
    T0
    ; tool H0.250 W0.400
    ; skirt
    G1 X24.600 Y-21.776 F4800
    G1 E0.0000 F540
    G92 E0
    G1 X24.600 Y21.776 E2.8971 F1980
    G1 X24.509 Y21.997 E2.9130
    G1 X21.997 Y24.509 E3.1493
    G1 X21.776 Y24.600 E3.1652
    G1 X-21.776 Y24.600 E6.0623



  • Just did a M115
    Turns out:
    M115
    FIRMWARE_NAME: RepRapFirmware for Duet WiFi FIRMWARE_VERSION: 1.19 ELECTRONICS: Duet WiFi 1.0 FIRMWARE_DATE: 2017-08-14

    No homez.g file
    No homeall.g

    But homedelta.g

    ; Home Delta Printer

    G91 ; use relative positioning
    G1 S1 X1800 Y1800 Z1800 F2600 ; move all carriages up to the endstops
    G1 S2 X-4 Y-4 Z-4 ; move carriages down 4mm
    G1 S1 X4 Y4 Z4 F200 ; move carriages slowly up 4mm to the endstops
    G1 Z-4 F2000 ; down a few mm so that we can centre the head
    G90 ; back to absolute positioning
    G1 X0 Y0 F2200 ; centre the head and set a reasonable feed rate



  • Something just struck me as odd.

    Why does the head touch a piece of paper firmly at 0.1mm z height.
    And yet the G30 S-1 report -0.451 consistently.
    Shouldn't they be roughly the same ?

    The JohnSL probe kit included 6 rubber round pads (2 for each sensor).
    These seem to make pressing on the bed feel a little dampened or "squishy".
    Is this the problem ?

    Thx

    Pete




  • administrators

    @peteihughes Thanks for the comprehensive information.

    you should calibrate the delta printer before you probe the bed for mesh bed levelling. It is not clear if you have done this yet. Basically calibrating the delta sorts out all the variables for M666 and M665 that define the geometry of the printer. You have a Bed.g with 6 factor calibration setup already so have a look here:

    https://duet3d.dozuki.com/Wiki/Calibrating_a_delta_printer#Section_Running_auto_calibration_for_the_first_time

    Once the printer is calibrated nicely, trt rerunning G29 (the mesh bed levelling) and post a picture of the heightmap here.



  • @t3p3tony
    Thx for the reply.

    This printer is a few months old.
    I have printed many fairly accurate benchys and calibration cubes with it.
    But I was never thrilled with the first layer (usually a "fraction" low in one corner),
    so I decided to go with the JohnSL for zprobing.
    Never z probed before.

    If I set G31 Z param to 0.1, even now, I get good prints.

    Prior to zprobing,
    my config.g file did not have
    G31 set to Z-0.451
    It was set to zero or not even there.

    And there was never a crash.

    Now it does, because I followed
    https://duet3d.dozuki.com/Wiki/Calibrating_a_delta_printer

    I zero out Z in G31 in the config.g
    jog the head to touch a piece of paper (this is at 0.1mm z height)
    send a G92 Z0
    Head up 10mm
    send G30 S-1 multiple times
    This results in a value -0.451 consistently
    I then put this value into config.g like so
    G31 X0 Y0 Z-0.451 P250 ; set the zprobe height and threshold.

    And every print crashes.

    So, I believe my issue is with the G30 S-1 returning -0.451,
    and me setting G31 Z to -0.451.

    I know this is not a Duet problem per-se.
    But I don't know where else to look.

    As I mentioned, if I set G31 Z param to 0.1, even now, without z-probing,
    I get good prints.

    Is this a JohnSL problem, G31 P250 threshold or what.

    I though zprobing was going to be an end to my issues, but alas.



  • If you tell the printer to move to Z0, where does the nozzle end up?

    A negative value for G31 Z means that the probe is triggering below the surface of the bed, which makes sense given that your probe has some squishy pads and depends on the bed pressing down.

    I'm not familiar with the JohnSL probe, but you may be able to increase it's sensitivity by increasing the probe speed slightly in your M558 F command or decreasing the trigger value in G31 P command.

    Right now your M558 command doesn't have a speed parameter. I'm not sure what your default Z axis feed rate is, but it may be too high or too low.

    Right now your G31 P trigger value is 250. Try 100 or 50 and repeat the G30 S-1 test and see if the value returned gets close to 0.

    Personally, I wouldn't use a piece of paper to measure the Z0 position if you can visually move the nozzle to just touch the bed for a true representation of Z0.



  • @phaedrux and @T3P3Tony
    Great info guys.

    Currently in the middle of a print, so will try all suggestions in the morning.

    Thanks Again

    Pete


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