Help: New build homing improperly on Z axis



  • So i just finished a build based on the HEVO using a duet 2 wifi w/ a Duex5 and triple independent Z steppers. I finally have all the motion moving the right way (bed drops away from the nozzle when homing and then moves up), the bed goes up to 0 and down to 500, the issue is when i try to home it, it tries to home at 500 (the bottom of the printer) even tho when it homes it will set that to 0.

    ; Endstops
    M574 X1 Y1 S0 ; set active low and disabled endstops
    M574 Z2 S0

    ; Drives
    M584 X0 Y1 Z2:5:6 E3:4 ; set drive mapping
    M671 X-40:440:440 Y185:325:30 S1 ; leadscrews
    M569 P0 S1 ; physical drive 0 goes forwards
    M569 P1 S1 ; physical drive 1 goes forwards
    M569 P2 S0 ; physical drive 2 goes backwards
    M569 P3 S1 ; physical drive 3 goes forwards
    M569 P4 S1 ; physical drive 4 goes forwards
    M569 P5 S0 ; physical drive 5 goes backwards
    M569 P6 S0 ; physical drive 6 goes backwards

    ; homez.g
    ; called to home the Z axis
    ;
    ; generated by RepRapFirmware Configuration Tool v2.1.8 on Wed Mar 11 2020 21:21:21 GMT-0500 (Central Daylight Time)
    G91 ; relative positioning
    G1 H2 Z5 F6000 ; lift Z relative to current position
    G1 H1 Z505 F3600 ; move Z up until the endstop is triggered
    G92 Z0 ; set Z position to axis minimum (you may want to adjust this)

    ; Uncomment the following lines to lift Z after probing
    ;G91 ; relative positioning
    ;G1 Z5 F100 ; lift Z relative to current position
    ;G90 ; absolute positioning



  • @Holyman92 said in Help: New build homing improperly on Z axis:

    G1 H2 Z5 F6000 ; lift Z relative to current position

    Your homing moves are backwards. Increasing Z makes the nozzle/bed separation larger. To make that spread larger on a HEVO (and other moving bed CoreXY), the bed drops as Z increases.

    You want -5 on this move and -505 on your endstop move. Moving Z to smaller numbers (negative relative moves) moves the bed closer to the nozzle; in other words, up.



  • @Danal said in Help: New build homing improperly on Z axis:

    You want -5 on this move and -505 on your endstop move. Moving Z to smaller numbers (negative relative moves) moves the bed closer to the nozzle; in other words, up.

    now it moves up towards the nozzle when i home but when u add 5 to the z it moves up instead of down


  • Moderator

    @Holyman92 said in Help: New build homing improperly on Z axis:

    Your first 5mm move is correct as positive. The 505mm move must be negative.



  • Correct. I forgot the first move is to move it away from everything.

    Also, the -505... it is sort of tradition to do -999999 or similar. This makes it very obvious that this move is a home move, and the switch will end it.

    Also, if your bed ever happened to be beyond 505 down (crammed into the bottom, for whatever reason), homing would fail with a -505, and frustratingly enough, fail JUST before it touched the switch!

    Anyway, that's the two reasons for -999999


  • Moderator

    @Danal said in Help: New build homing improperly on Z axis:

    Anyway, that's the two reasons for -999999

    That's a little extreme. If the switch fails your axis will grind away for the entire duration of the move. Maybe something a little closer to the axis length but still longer. 600 maybe?


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