BLTouch for LK1/LK4/LK4 PRO/LK5 PRO Leveling

BLTouch for LK1/LK4/LK4 PRO/LK5 PRO Leveling


This article is to help the LONGER LK and LK Pro series 3d printers users who want to upgrade with auto bed leveling sensor, like BL-TOUCH, etc. More information about senor please refer to the sensor datasheet.




  • LONGER FDM 3D Printer LK or LK Pro series
  • BL-TOUCH or other similarsensor
  • Sensor attached wires(5pin)
  • Sensorattached screws and nuts(2 pairs)
  • Sensor mount(printed .stlmodel)
  • USB cable
  • Pronterface or other serial port communication software
  • 50k ohm or 100k ohm resistor(LKx series users only)
  •                                                                                                                                             LK Pro series needs electrical tape to cover the +5V pin. as the picture shows.





  1. Switch-off the printerpower
  2. Find the position of motherboard, then screw down the mother board cover. 
  3. Unplugthe Z-MIN wire(2 pin) in board
  4. 4.Hook up the sensor and the motherboard. LKx series users need parallel a 50 or 100 k ohm resistor between 5V pin and PWM pin as the picture showing below
  5. Screw up the mother boardcover

 bl touch mainboard

                                                                                                                                                                                                                                     LKx series board wiring need extra resistor

LK4 PRO/LK5 PRO mainboard wiring

                                                                                                                                                                                                                                                                                             LKx Pro series board wiring


  1. Removethe Z axis end stop switch as picture showing below


                                                                                                                                                                                                                                                                   Remove the z min end stop switch

2. Screwdown left 2 screws of head module

3. Mount BL-TOUCH as picture showing below 

mounted bltouch to 3d printer

                                                                                                                                                                                                                                                                                                                   Mount sensor

 Power on

  1. Confirm BL-TOUCH wiring and mounting iscomplete
  2. Switch on the printer power
  3. ConnectPC and printer with USB-cable
  4. Flash BL-TOUCH dedicated firmware .Check the firmware update manual if you need.
  5. Open pronterface software, select serial port(115200 baudrate). and connect to printer


Adjusting z-offset

  1. Clean up bed and nozzle, and ensure no materials stick on 
  2. Send M851 Z0 to reset Z offset value  
  3. Send G28 to homing XYZ axis
  4. Send G1 F60 Z0 to lower Z axis to the software origin 
  5. Send M211 S0 to inactivate software endstop function
  6. Place a sheet of paper (or other block of 0.10mm approximately) on the bed and use the pronterface to lower the nozzle 1mm by 1mm then 0.1mm by 0.1mm until you feel a friction on the sheet of paper (the paper is not to be jammed but not too free either). Then remove the sheet.
  7. Send M114 to get current Z height value(usually negative). the value is the z-offset we need.
  8. Send M851 Z x.x to set z-offset(x.x is the value of previous value)
  9. Send M500 to save current settings.
  10. 10.Send M211 S1 to re-activate software endstop function 
  11. Send G28 Z0 to homing Z axis
  12. 12.Send G1 F60 Z0 to test if Z axis could back to the actual Z origin by checking the clearance between bed and nozzle if is about 0.1 mm (thickness of a sheet of paper). If not, please repeat step 1 to 11.


Adjusting auto leveling

1.Send G28 to homing XYZ axis.
2. Send G29, and waiting for bed tilt measurement to complete.
3.Send M500 to save measurement values of previous step.
4.Send M420 S1 to activate auto leveling function.


    Replace GCODE

    1. Replacewith new START GCODE(in appendix section) in your slicer software(Cura, Slic3r, Simplify3D, )
    2. Have fun! :)


    G21 ; metric values
    G90 ; absolute positioning
    M82 ; set extruder to absolute mode
    M107 ; start with the fan off
    ; confirm BL-touch safety
    M280 P0 S160 ; BL-Touch Alarm release
    G4 P100 ; Delay for BL-Touch homing
    G28 X0 Y0 ; move X/Y to min endstops
    G28 Z0 ; move Z to min endstops
    ; reconfirm BL-touch safety
    M280 P0 S160 ; BL-Touch Alarm realease
    G4 P100 ; Delay for BL-Touch
    ; bed leveling
    G29; Auto leveling
    M500 ; save data of G29 and M420
    M420 S1 ; enable bed leveling
    ; prepare hot-end
    G92 E0 ; Reset Extruder
    G1 Z2.0 F3000 ; Move Z Axis up little to prevent scratching of Heat Bed
    G1 X0.1 Y20 Z0.3 F5000.0 ; Move to start position

    G1 X0.1 Y150.0 Z0.3 F1500.0 E15 ; Draw the first line

    G1 X0.4 Y150.0 Z0.3 F5000.0 ; Move to side a little

    G1 X0.4 Y20 Z0.3 F1500.0 E30 ; Draw the second line

    G92 E0 ; Reset Extruder

    G1 Z2.0 F3000 ; Move Z Axis up little to prevent scratching of Heat Bed

    G1 X5 Y20 Z0.3 F5000.0 ; Move over to prevent blob squish
    ; -- end of BL-TOUCH START GCODE -- 



    Files Download:

    PC Software: >>pronterface-windows<<

    Mouted Bracket: >>Bracket<<

    The firmwares has been codeed by LONGER, you would download the firmware and upgrade directly:

    >>For LK1(U20)<<

    >>For LK1 Plus(U20 Plus)<<

    >>For LK4(U30)<<

    >>For LK4 PRO(U30 Pro)<<

    >>For LK5 PRO<<


    If you have install dual blower kit, use dual blower kit Mouted Bracket: >>Bracket<<, and download below firmware and upgrade directly:

    >>For LK1(U20)<<

    >>For LK1 Plus(U20 Plus)<<

    >>For LK4(U30)<<

    >>For LK4 PRO(U30 Pro)<<

    >>For LK5 PRO<<




    If there's any question or need assistance from us on the upgrade, please feel free to contact us at, LONGER support team will follow up and reply you ASAP.


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