Z-offset with BL Touch



  • Hi all,

    I've tried to find answers to this from other questions but am still unsure so thought I'd better ask..

    I'm having trouble with my z offset (BL touch probe). I'm currently using manual bed levelling and no mesh calibration.

    So I get my bed levelled manually by probing with G30, then sending G1Z0 at the corners and centre of the bed (glass) and using thumbscrews to adjust the bed height. I then repeat this process a couple of times to ensure all locations are as close to 0.1mm from the bed as possible.

    Then I start printing and instantly the nozzle crashes into the bed and I have to raised the bed using the baby height adjustments to around 0.8mm. I don't understand what is causing this problem. Hopefully the following system files and print g-code should help identify the issue?

    config.g

    ; Configuration file for Duet WiFi (firmware version 1.20 or newer)
    ; executed by the firmware on start-up
    ;
    ; generated by RepRapFirmware Configuration Tool on Wed Mar 07 2018 10:07:16 GMT+0000 (GMT)
    
    ; General preferences
    G90                                                                            ; Send absolute coordinates...
    M83                                                                            ; ...but relative extruder moves
    M555 P1                                                                        ; Set firmware compatibility to look like RepRapFirmare
    
    ; Network
    M550 Pxxxxxxx                                                           ; Set machine name
    M551 Pxxxxxxx                                                              ; Set password
    M552 S1                                                                        ; Enable network
    M586 P0 S1                                                                     ; Enable HTTP
    M586 P1 S0                                                                     ; Disable FTP
    M586 P2 S0                                                                     ; Disable Telnet
    
    ; Drives
    M569 P0 S0                                                                     ; Drive 0 goes backwards
    M569 P1 S1                                                                     ; Drive 1 goes forwards
    M569 P2 S1                                                                     ; Drive 2 goes forwards
    M569 P3 S1                                                                     ; Drive 3 goes forwards
    M350 X16 Y16 Z16 E16 I1                                                        ; Configure microstepping with interpolation
    M92 X80 Y80 Z400 E199.99                                                       ; Set steps per mm
    M566 X480 Y480 Z12 E120                                                        ; Set maximum instantaneous speed changes (mm/min)
    M203 X9001 Y3000 Z600 E3000                                                    ; Set maximum speeds (mm/min)
    M201 X800 Y800 Z100 E5000                                                      ; Set accelerations (mm/s^2)
    M906 X760 Y900 Z760 E1500 I30                                                  ; Set motor currents (mA) and motor idle factor in per cent
    M84 S30                                                                        ; Set idle timeout
    
    ; Axis Limits
    M208 X0 Y0 Z0 S1                                                               ; Set axis minima
    M208 X190 Y200 Z175 S0                                                         ; Set axis maxima
    
    ; Endstops
    M574 X1 Y1 S0                                                                  ; Set active low endstops
    
    ; Z-Probe
    M307 H3 A-1 C-1 D-1 ;
    M558 P9 H5 F160 R0.250 T2000 A3                                                ; Set Z probe type to bl touch and the dive height + speeds
    G31 X41 Y-47 Z3.25 P25                                                         ; Set Z probe trigger value, offset and trigger height
    M557 X18:182 Y18:182 S25                                                       ; Define mesh grid
    
    ; Heaters
    M301 H0 S1.00 P10 I0.1 D200 T0.4 W180 B30                                      ; Use PID on bed heater (may require further tuning)
    M305 P0 T100000 B3988 C0 R4700                                                 ; Set thermistor + ADC parameters for heater 0
    M143 H0 S120                                                                   ; Set temperature limit for heater 0 to 120C
    M305 P1 T100000 B4725 C0 R4700                                                 ; Set thermistor + ADC parameters for heater 1
    M143 H1 S280                                                                   ; Set temperature limit for heater 1 to 280C
    M307 H0 A90.0 C700.0 D10.0 S1.00 V0.0 B1                                       ; PID tuning - set automatically (M303) and moved from config-override.g
    M307 H1 A458.2 C201.5 D3.2 S1.00 V24.0 B0                                      ; PID tuning - set automatically (M303) and moved from config-override.g
    M307 H2 A340.0 C140.0 D5.5 S1.00 V0.0 B0                                       ; PID tuning - set automatically (M303) and moved from config-override.g
    M307 H4 A340.0 C140.0 D5.5 S1.00 V0.0 B0                                       ; PID tuning - set automatically (M303) and moved from config-override.g
    M307 H5 A340.0 C140.0 D5.5 S1.00 V0.0 B0                                       ; PID tuning - set automatically (M303) and moved from config-override.g
    M307 H6 A340.0 C140.0 D5.5 S1.00 V0.0 B0                                       ; PID tuning - set automatically (M303) and moved from config-override.g
    M307 H7 A340.0 C140.0 D5.5 S1.00 V0.0 B0                                       ; PID tuning - set automatically (M303) and moved from config-override.g
    
    ; Fans
    M106 P0 S0 I0 F500 H-1                                                         ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
    M106 P1 S1 I0 F500 H T45                                                       ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P2 S1 I0 F500 H T45                                                       ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned on
    
    ; 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
    
    ; Automatic saving after power loss is not enabled
    
    ; Custom settings are not configured
    M572 D0 S0                                                                     ; Disable Pressure Advance
    
    ; Miscellaneous
    T0                                                                             ; Select first tool
    

    homeall.g

    ; homeall.g
    ; called to home all axes
    ;
    ; generated by RepRapFirmware Configuration Tool on Wed Mar 07 2018 10:07:16 GMT+0000 (GMT)
    M280 P3 S160 I1         ; Z probe alarm release
    ; M280 P3 S10 I1          ; deploy Z probe
    G91                     ; relative positioning
    G1 S2 Z5 F6000          ; lift Z relative to current position
    G1 S1 X-205 Y-205 F6000 ; 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-205 Y-205 F600  ; move slowly to X and Y axis endstops once more (second pass)
    G90                     ; absolute positioning
    G1 X59 Y147 F6000       ; go to probe point - centre of bed
    G30                     ; home Z by probing the bed
    
    G1 Z5 F100.             ; uncomment this line to lift the nozzle after homing
    

    homez.g

    ; homez.g
    ; called to home the Z axis
    ;
    ; generated by RepRapFirmware Configuration Tool on Wed Mar 07 2018 10:07:16 GMT+0000 (GMT)
    M280 P3 S160 I1    ; Z probe alarm release
    ; M280 P3 S10 I1     ; deploy Z probe
    G91                ; relative positioning
    G1 S2 Z5 F6000     ; lift Z relative to current position
    G90                ; absolute positioning
    G1 X59 Y147 F6000  ; go to probe point - centre of bed
    G30                ; home Z by probing the bed
    
    G1 Z5 F6000        ; lift Z after homing
    

    print_file.gcode

    ; G-Code generated by Simplify3D(R) Version 4.0.0
    ; Jun 2, 2018 at 3:33:59 PM
    ; Settings Summary
    ;   .... abbreviated for brevity
    G90
    M83
    M106 S0
    M140 S55
    M190 S55
    M104 S215 T0
    M109 S215 T0
    G28                                    ; Home all
    M561                                  ; Clear any bed transform that might be in place
    ;G29 S1                               ; Load bed mesh analysis
    G1 Z5 F6000                     ; Move Z to 5
    G1 X5 Y5                            ; Move Head to front left
    G92 E0                               ; Zero Extruder
    G1 F200 E4                        ; Prime the extruder
    G92 E0                               ; Zero Extruder
    G1 E-2.0000 F3000
    G1 Z0.180 F1002
    ; process Process1-1-5
    ; layer 1, Z = 0.180
    T0
    ; tool H0.200 W0.528
    ; skirt
    G1 X84.105 Y87.840 F9000
    G1 E1.8000 F900
    G1 X105.895 Y87.840 E0.9566 F720
    G1 X107.160 Y89.105 E0.0786
    G1 X107.160 Y110.895 E0.9566
    G1 X105.895 Y112.160 E0.0786
    ....

  • administrators

    Check that the trigger height of the bltouch remains constant when you probe the bed multiple times in the same spot using G30 S-1. If it doesn't, then you may need to reduce the probing speed (F parameter in the M558 command).


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