Z offset issue



  • Trying to run my first test print after programming a duet for my first time. Using a BLtouch which is working perfectly for homing etc.
    Problem is when I go to print the nozzle is too close to the bed. I have to raise it up clicking on the offset button under the print job to about .7. I have tried changing my Z offset on G31 line raising it up from the initial 1.75 that was calculated when installing the bltouch, now it is up 2.25 and it still is not changing.

    Something in my code must be overiding it or conflicting.

    ; General preferences
    M111 S0 ; Debugging off
    G21 ; Work in millimetres
    G90 ; Send absolute coordinates…
    M83 ; ...but relative extruder moves
    M555 P2 ; Set firmware compatibility to look like Marlin
    M208 X0 Y0 Z0 S1 ; sets the minimum values for all axes
    M208 X300 Y300 Z400 S0 ; sets the maximum values for all axes

    ; Endstops
    M574 X1 Y1 S1 ; X home to min. Y home to min. Normally Closed limit switches.
    M574 Z1 S2 ; Define Z to use Probe. Home to Min
    M558 P5 H7 F200 T4000 X0 Y0 Z1 ; Set Z probe type/mode 5. H=Dive Height. F=Speed the bed moves
    G31 P25 X-38 Y-8 Z2.25 ; Z probe trigger value, offset in relation to nozzle. And trigger height adjustment
    M557 X20:280 Y20:280 S80 ; Define mesh grid

    ; Drives
    M569 P0 S0 ; Drive 0 goes backwards
    M569 P1 S0 ; Drive 1 goes backwards
    M569 P2 S0 ; Drive 2 goes forwards
    M569 P3 S0 ; Drive 3 goes backwards
    M350 X16 Y16 Z16 E32 I1 ; Configure microstepping with interpolation
    M92 X80 Y80 Z400 E202.2 ; Set steps per mm
    M566 X1200 Y1200 Z24 E300 ; Set maximum instantaneous speed changes (mm/min)
    M203 X30000 Y30000 Z600 E5000 ; Set maximum speeds (mm/min)
    M201 X500 Y500 Z100 E5000 ; Set accelerations (mm/s^2)
    M906 X800 Y800 Z700 E800 I30 ; Set motor currents (mA) and motor idle factor in per cent
    M84 S30 ; Set idle timeout

    ; Heaters
    M143 S265 ; Set maximum heater temperature to 265C
    M305 P0 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 0
    M305 P1 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 1

    ; BLTouch - Heaters
    M307 H7 A-1 C-1 D-1 ; Disable the 7th Heater to free up PWM channel 5 on the Duex board

    ; Tools
    M563 P0 D0 H1 ; Define tool 0
    G10 P0 X0 Y0 Z0 ; Set tool 0 axis offsets
    G10 P0 R0 S0 ; Set initial tool 0 active and standby temperatures to 0C

    ; Network
    M550 PCR10SDuet ; Set machine name
    M552 S1 ; Enable network
    M586 P0 S1 ; Enable HTTP
    M586 P1 S0 ; Disable FTP
    M586 P2 S0 ; Disable Telnet

    ; Fans
    M106 P0 S1 I0 F500 H1 T50 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P1 S0 I0 F30 H-1 ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned off - have 2 Blowers parallel
    M106 P2 S0.5 I0 F30 H-1 ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned off - have 2 Case Fans parallel

    ; Custom settings
    M912 P0 S-13 ; calibrate MCU Temp

    ; Miscellaneous
    M501 ; with PID Tune data
    T0 ; Select first tool

    ; homeall.g
    ; called to home all axes
    ;
    ; generated by RepRapFirmware Configuration Tool on Sat Oct 28 2017 00:02:03 GMT+0200 (Mitteleuropäische Sommerzeit)

    ; Relative positioning
    G91

    ; Course home X and Y
    G1 X-305 Y-305 F3600 S1

    ; Fine home X and Y
    G1 X-305 Y-305 F3000 S1

    ; Move away from the endstops
    G1 X50 Y50 F3000

    ; Homez.g
    ; Move away from the endstops
    G1 X150 Y150 F6000
    G30 ; Do a single probe to home our Z axis
    G91
    G1 Z20 F3000 ; Rapidly move the Z axis to Z=20

    And here is my start code in Cura:

    G28 XY ;Home XY
    M561
    G1 X104.5 Y130 ; Move Probe to middle of bed
    G30 ; Do a single probe
    G1 X30 Y30 F9000 ;Go to purge start position
    G1 Z0.2 ;Drop to bed
    G92 E0 ;Reset E position
    G1 X50 E25 F1200 ;Draw purge line
    G1 X200 F7200 ;Wipe out
    G92 E0 ;Reset E position



  • How do I permanently disable using mesh bed leveling to eliminate that from the equation? i have a glass bed with solid mounts so i dont see the need for that anyway.



  • @57buick said in Z offset issue:

    M558 P5

    For the BLTouch you should be using probe type P9.

    I can't quite tell from you rpost, but does your homeall contain the homez portion to home the z axis, or is that seperate and only used in homez?

    It doesn't look like you have a G29 anywhere to run mesh compensation or load a saved heightmap, so I don't think it's being used. You can check by sending M122 to get a diagnostic read out, and look for where it says Compensation used: none/mesh. Plus you have M561 in your Cura start code which should clear any compensation if it were active.

    I think it's a little odd to use G30 in the Cura start code. You should probably just have your homing script setup in homeall and use G28 to home all axis before the print.

    I think it would help to know exactly how you went about measuring the Z probe trigger height in the first place, as this could explain where the discrepancy is coming from.

    A few tips to remember:

    • Make sure the point you are measuring the trigger height is the same point you will use when homing, and ideally it should be in the center of your bed.
    • When measuring the trigger height both your nozzle and bed should be at temperature so that the effects of thermal expansion/warping are taken into account.
    • Because the BLTouch is offset from the nozzle, if your bed has any tilt or warp, the trigger distance between where the nozzle is and the probe touches could be different, so ideally you should set Z0 with the nozzle touching the bed, and then move the probe over in X and Y so that it's directly over that same point when you use G30 S-1 to measure the trigger height.


  • I used these instructions to setup the bltouch and find my Z offset which came out to a 1.75 offset. So i put 1.75 on my G31 line. I have since changed that line to 2.25 and still not getting in change in nozzle height.

    https://betrue3d.dk/bltouch-on-duet-wifi-configuratio-and-usage/

    per your comment I eliminated the following lines from my Cura start code and I will see what happens
    G1 X104.5 Y130 ; Move Probe to middle of bed
    G30 ; Do a single probe



  • @57buick Hey if you want to lift the nozzle after calibration, your trigger height must become smaller, not bigger.
    So maybe try something like Z1.65 or 1.61



  • @nightreaver said in Z offset issue:

    @57buick Hey if you want to lift the nozzle after calibration, your trigger height must become smaller, not bigger.
    So maybe try something like Z1.65 or 1.61

    Ill try it, but the instructions specifically say with a probe like the BLtouch the offset will go positive? but maybe I misinterpreted that, ill give it a try though, thanks



  • @nightreaver said in Z offset issue:

    @57buick Hey if you want to lift the nozzle after calibration, your trigger height must become smaller, not bigger.
    So maybe try something like Z1.65 or 1.61

    OMG! @Nightreaver I feel like an idiot, you were right I needed to go more negative. Everything I read on how to setup the bltouch and configuring the offset seemed to indicate I needed to go positive to move the nozzle up and also on the job status page on the web interface I had to click "positive" up in .05 increments until filament could come out so it was very misleading. Thanks for your help, my first print is running now we will see how it comes out


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