[BUG]

[campbellollie]

Hi everyone,

I'm trying to finally resolve an issue that has plagued me for a long time regarding BLTouch and my Anycubic i3 Mega configuration. It seems no matter what I try I'm unable to get the Z-offset correct when using my BLTouch and "AUTO_BED_LEVELING_BILINEAR".

Some background:

• The BLTouch is installed and when retracted the needle is about 2-2.3mm above the nozzle height.
• I'm using this firmware.
• Homing the printer brings the nozzle level with the bed.

The problem:
Whenever I print after a G29 levelling, the nozzle is always 4-5mm above the bed.

My levelling process:

• From a freshly flashed (and rebooted) printer
• Check the X gantry is level and homing correctly.
• Check that both Z-axis end stops are trigged at the same time
• Check that the nozzle is level with the bed when homed
• Manually level the bed with a piece of paper
• G28
• G29 (using the built in Special Menu automatic bed levelling)
• Save to EEPROM (Using the built in Special Menu)
• Move the nozzle to 5 cm above the centre of the bed
• M211 S0
• Manually jog the Z axis down until it catches a piece of paper
• M114 to get the Z-offset
• M851 Z with the result from the step above
• M500
• M501
• Reboot the printer
• Try and print

The only configuration changes I make to the Marlin config are:
*PID values for the hotend and heated bed

• Calibrated motor steps
• Offset settings for the probe:
  #define X_PROBE_OFFSET_FROM_EXTRUDER -2 // X offset: -left +right [of the nozzle]
  #define Y_PROBE_OFFSET_FROM_EXTRUDER -23 // Y offset: -front +behind [the nozzle]
  #define Z_PROBE_OFFSET_FROM_EXTRUDER -2

Here's my start code:

G28 ;Home
;M501 ;Load bed levelling settings
M420 S1 ;Use bed levelling settings
G21 ;metric values
G90 ;absolute positioning
M82 ;set extruder to absolute mode
M107 ;start with the fan off
G1 Z5.0 F9000 ;move the head 5mm up for clearance
G92 E0 ;zero the extruded length
G1 F200 E3 ;extrude 3mm of feed stock
G92 E0 ;zero the extruded length again
M117; Printing...
G5;

I've followed numerous guides, YouTube videos etc etc and still seem to have the same problem.

[DeadSix27]

Are you still maintaining this repo? I face the same issue as the above person.. I tried testing out various Z offsets just out of pure frustration .. M851 Z-8.9, M851 Z8 neither going very high or low rly has an effect.. the needle is always quite far up..
do we have to actually turn the screw on the bltouch? but even then.. why would the zoffset not have a big impact, surely if u ramp it up to like -10 or +10 it should be way above the bed or scratch it?