First print scrapes bed?



  • I've set the z stop and bed height so that on homing Z the hot end nozzles are the thickness of the Duet business card away from the buildTak surface.

    However, when I try and print, the head scrapes hard into the surface of the buildTak - nearly wrecking it. I can't understand why. Are you supposed to enter the height after homing as the Z offset?



  • When you home your machine, do you have to move the Z axis to get it where you want or are you homing to Z0?



  • I click home all, it goes to the right place. The bed is just the thickness of a card below the hot ends after everything stops.

    This is where I'm a bit confused, does the duet now think it's at Z0, when in fact the hot ends are above the bed?



  • Can you post your home all and homez configs?



  • homez:

    [[language]]
    ; homez.g
    ; called to home the Z axis
    ;
    ; generated by RepRapFirmware Configuration Tool on Fri Feb 16 2018 16:17:02 GMT+0000 (GMT)
    G91                 ; relative positioning
    G1 Z5 F480000       ; lift Z relative to current position
    G1 S1 Z-195 F180000 ; move Z down until the switch triggers
    G92 Z2.5            ; set Z position to trigger height
    
    ; Uncomment the following lines to lift Z after probing
    ;G91                ; relative positioning
    ;G1 Z5 F8000        ; lift Z relative to current position
    ;G90                ; absolute positioning
    
    

    home all:

    [[language]]
    ; homeall.g
    ; called to home all axes
    ;
    ; generated by RepRapFirmware Configuration Tool on Fri Feb 16 2018 16:17:02 GMT+0000 (GMT)
    G91                       ; relative positioning
    G1 Z5 F480000             ; lift Z relative to current position
    G1 S1 X-205 Y-205 F180000 ; move quickly to X and Y axis endstops and stop there (first pass)
    G1 X5 Y5 F480000          ; go back a few mm
    G1 S1 X-205 Y-205 F25200  ; move slowly to X and Y axis endstops once more (second pass)
    G1 S1 Z-195 F180000 S1    ; move Z down stopping at the endstop
    G90                       ; absolute positioning
    G92 Z2.5                  ; set new Z position
    ;G1 Z5 F8000              ; uncomment this line to lift the nozzle after homing
    
    

    I have bought DC42's probe but not fitted yet (need to first print the chimera mount!). So I'm a bit confused by lines like the G92 there. Do I need to change that value to the real height above the bed after homing?


  • administrators

    According to your homing files, your Z homing switch triggers when the nozzle is 2.5mm above the bed. Is that the figure you measured?



  • No, not sure where that figure came from.

    I manually levelled the bed after homing z so that it would be the thickness of Duet card (that came in the box) away from the buildTak as I seem to remember from using buildTak a long time ago that was the recommended distance.

    Should I enter that height in place of the 2.5mm?

    This is just to get a first print of the chimera probe mount - after that I'll use the probe hopefully to get the bed height correct!



  • Yes, change that to G92 Z0. If you really want Z0 to be the nozzle touching the bed and not paper then it will need to be G92 Z.1 (assuming you used a standard piece of copy paper)



  • @tjb1:

    Yes, change that to G92 Z0. If you really want Z0 to be the nozzle touching the bed and not paper then it will need to be G92 Z.1 (assuming you used a standard piece of copy paper)

    Not certain I understand. Buildtak say we recommend using the thickness of a standard piece of office paper (or about .1mm) for ABS and a piece of card stock (or about .2mm) for PLA.. So to get that I home Z, then manually level the bed to the thickness of a piece of card away from the nozzle. And finally in my homez file I put:

    [[language]]
    G92 Z.2
    
    ```Is that right?

  • administrators

    The value in those G92 commands should be the height at which movement stops when homing Z. So:

    1. Home Z.

    2. Read off the Z height in DWC (which should be 2.5), call this height#1

    3. Jog the head down until it is just touching the bed or just gripping a piece of paper.

    4. Read off the height again, call this height#2

    5. The correct value in those G92 commands is height#1 - height#2.



  • Brilliant - thank you!


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