Inconsistent trigger heights



  • I am trying to understand the inconsistent trigger heights when probing around by bed "P3 Steel with Bltouch", I am getting consistent results when just probing the centre of the bed several times though, so the probe seems ok.

    BLC 2.147 BRC 2.244
    Mid 2.130
    FLC 2.051 FRC 2.244

    First layer is always high on the back right side of the bed with mesh bed leveling unable to compensate correctly.
    I am quite new to 3D printing and don't quite understand this, I guess mechanical issue, any insights?

    Config.g; Configuration file for Duet Ethernet (firmware version 1.20 or newer)
    ; executed by the firmware on start-up
    ;
    ; generated by RepRapFirmware Configuration Tool on Wed May 09 2018 17:32:07 GMT+0100 (GMT Summer Time)

    ; General preferences
    G90 ; Send absolute coordinates...
    M83 ; ...but relative extruder moves
    G21 ; Work in millimetres
    M83 ; ...but relative extruder moves
    M555 P2 ; Set output to look like Marlin
    ; M575 P1 B57600 S1 ; Comm's parameters for PanelDue
    M912 P0 S-7.7 ; calibrate CPU temp

    ; Network
    M550 PP3 Steel ; Set machine name
    M552 P192.168.1.90 S1 ; Enable network and static dynamic address
    M586 P0 S1 ; Enable HTTP
    M586 P1 S0 ; Disable FTP
    M586 P2 S0 ; Disable Telnet

    ; Drives
    M569 P0 S1 ;C65972 ; Drive 0 goes forwards
    M569 P1 S1 ;C65972 ; Drive 1 goes forwards
    M569 P2 S1 ;C65972 ; Drive 2 goes forwards
    M569 P3 S0 ;C65972 ; Drive 3 goes backwords
    M569 P4 S1 ;C65972 ; Drive 4 goes forwords
    M584 X0 Y1 Z2:4 E3 ; X uses driver 0, Y driver 1, Z drivers 2 and 4, E driver 3
    M350 X16 Y16 Z16:16 E16 I1 ; Configure microstepping with interpolation
    M92 X160 Y160 Z803:803 E827 ; Set steps per mm

    M671 X300:-50 Y190:190 S2 ; leadscrews at left, right
    M204 P400 T1000 ; Lower accelerations when printing though
    M566 X600 Y600 Z24:24 E900 ; Set maximum instantaneous speed changes (mm/min) Max Jerk
    M203 X6600 Y6600 Z800:800 E3000 ; Set maximum speeds (mm/min)
    M201 X2000 Y2000 Z100:100 E3000 ; Set accelerations (mm/s^2)
    M906 X1100 Y1100 Z930:930 E1100 I30 ; Set motor currents (mA) and motor idle factor in per cent
    M84 S30 ; Set idle timeout
    M572 D0 S0.05 ; pressure advance
    M207 S1.2 R0 F2700 ; firmware retraction
    M208 S0 F600 ; set retraction recover speed / adjustments

    ; Axis Limits
    M208 X10 Y5 Z0 S1 ; Set axis minima
    M208 X270 Y229 Z214 S0 ; Set axis maxima

    ; Endstops
    M574 X1 Y1 S3 ; Set active high endstops, use sensorless homing
    M915 X Y S30 R2 F1 ; set X and Y to sensitivity 30, pause when stall, filtered

    ; Z-Probe
    M307 H3 A-1 C-1 D-1 ; DISABLE HEATER 3, FREE UP pwm CHANNEL 3 BLTOUCH

    M574 Z1 S2 ; Set Z endstop controlled by probe
    M558 P9 H5 F80 T2000 ; BLTOUCH Set Z probe type to unmodulated and the dive height + speeds
    G31 P5 X-31 Y-37 Z2 ; BLTOUCH Set Z probe trigger value, offset and trigger height, ;INCREASE VALUE WILL LOWER NOZZLE CLOSER TO THE BED, DECREASE THIS VALUE WILL RAISE THE NOZZLE FROM THE BED
    M557 X15:270 Y15:229 S45 ; Define mesh grid
    M376 H10 ; Set bed compensation taper

    ; Heaters bed
    M301 H0 S1.00 P10 I0.1 D200 T0.4 W180 B30 ; Use PID on bed heater (may require further tuning)
    M305 P0 T100000 B3950 R4700 ; Set thermistor + ADC parameters for heater 0
    M143 H0 S120 ; Set temperature limit for heater 0 to 120C

    ;Hotend
    M307 H1 A373.1, C193.9, D4.2 S1 ; PID settings
    M305 P1 T100000 B4725 C7.060000e-8 R4700 ; Set thermistor + ADC parameters for heater 1
    M143 H1 S280 ; Set temperature limit for heater 1 to 280C

    ; Fans
    M106 P0 H-1 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P1 S1 I0 F500 H1 T45 ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P2 S1 I0 F500 H0 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

    ; Epilogue
    T0 ; select first hot end</redacted>

    ; Miscellaneous
    M501 ; Load saved parameters from non-volatile memory

    Bed.g, for Z axis calibration
    ; bed.g
    ; called to perform automatic bed compensation via G32

    G29 S2 ; to clear the height map before Z homing

    M400 ; make sure everything has stopped
    M913 X100 Y100 ; XY motors to 100% current
    G28 ; home
    M401 ; deploy Z probe
    G30 P0 X10 Y125 Z-99999 ; probe near a leadscrew
    G30 P1 X235 Y125 Z-99999 S2 ; probe near a leadscrew and calibrate 2 motors
    M402 ; retract probe

    M401 ; deploy Z probe
    G30 P0 X10 Y125 Z-99999 ; probe near a leadscrew
    G30 P1 X235 Y125 Z-99999 S2 ; probe near a leadscrew and calibrate 2 motors
    M402 ; retract probe

    G28 ; home all axes
    G29 ; Mesh bed leveling

    Results single spot probe
    M98 P"0:/macros/Repeat Z probe test"
    G32 bed probe heights: -0.019 -0.025 -0.020 -0.030 -0.036 -0.040 -0.031 -0.030 -0.032 -0.026 -0.039 -0.027 -0.026 -0.030 -0.027 -0.027 -0.027 -0.020 -0.020 -0.024 -0.016 -0.020 -0.019 -0.012 -0.014, mean -0.026, deviation from mean 0.007



  • Try adding B1 R0.1 A5 to your M558 command.

    That will turn off the heater during a probe move to eliminate any possible interference, pause 0.1 seconds between probes to allow the probe to settle completely, and probe up to 5 times until two consecutive probe results are within 0.03.

    That might help get some more consistency out of the BLTouch.

    You may also want to take the pin out of the housing by removing the set screw on the top of the BLTouch. Sometimes they need a bit of cleaning. It may also be possible the set screw is loose or out of ideal position. The set screw is what provides the electromagnet with a ferrous source to attract to.



  • Thank you for your help, I have also adjusted the height compensation which has sorted it out using G32, is it possible to do the same with G29 mesh bed levelling?

    ; Probe the bed at 5 points
    G30 P0 X40 Y20 Z-99999 H-0.104 ; define 4 points in a clockwise direction around the bed, starting near (0,0)
    G30 P1 X40 Y180 Z-99999 H0.035
    G30 P2 X210 y180 Z-99999 H0.165
    G30 P3 X210 Y20 Z-99999 S-0.039


  • administrators

    If the trigger height varies consistently with bed position, that suggests that the entire print head is tilting by an amount that varies with bed position. The tilt changes the relative heights of the probe and the nozzle, leading to an apparent change in trigger height.



  • " First layer is always high on the back right side of the bed with mesh bed leveling unable to compensate correctly. "

    If you place something known to be flat on the bed (glass is ideal) can you level the bed at all 4 corners, manually?

    Is this a machine where the bed moves horizontally for the X or Y axis (i3 style)?

    If so and if one corner is always high/low when leveled manually it sounds like one of the two linear guides the bed rides on could be bowed, or out of alignment with the other.

    I had this exact problem with one of my printers. This was a DIY build that somewhat resembles a CR10. I had originally used 2 parallel vlot slot extrusions as linear guides for the bed.

    One of the two V slot extrusions was bowed. This caused the front right corner of the bed to be low, when moved to the nozzle. Adjusting it would then make that corner of the bed high, when moved away. Solution in my case was to remove the bowed rail, and just use the good one.

    Hope this helps.



  • Yes it's an "P3 steel" i3 style printer and it does look like my X axis rods bow as I have now rotated them 90 deg and this has in turn has moved the pattern of low/high spots on the bed, so it looks like new rods and bearing are needed, I also checked for tilt as dc42 suggested but this seems ok.
    Than you guys for your help in diagnosing this issue as I am new to 3D printing and this is my first build.



  • @boldnuts Glad you got it sorted out. 3D printers will always provide new ways to tinker.


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