4 POINT LEVEL MENU - dennislia/Marlin-2-0-x-Anycubic-i3-MEGA-S-Fork GitHub Wiki
4 Point Level Menu:
Before selecting on the Special Menu:
- you may need to adjust the Z Adjustment Screw, so that the bed's Z limit switch doesn't prohibit the bed from being manually raised with the leveling screws during 4 Point Leveling or automatically raised under program control during Probe Z-Offset calibration. To do this, first loosen the Butterfly Nut and lower the Adjustable Screw, so that the limit switch won't be tripped when the bed is raised to it's maximum height. Then raise the bed to its maximum height by adjusting the bed leveling knobs. Next programmatically move the Nozzle down to touch a piece of paper on the bed, using the Z height controls on the TOOLS | XYZ LCD display. At this point raise the Adjustable Screw to almost trip the limit switch, and tighten the Butterfly Nut.
Lower the Adjustable Screw (allow the bed to go higher):
Raise the Adjustable Screw (limit the height the bed can go):
- next, you may need to adjust the bed to it's lowest level, using the bed leveling knobs, so that you have room to make subsequent programmatic nozzle adjustments when calibrating Probe Z-Offset.
NOTE: The maximum Z adjustment range of the bed is about 6.5mm and the worst case BLTouch probe Z-Offset could be as much as 6.6mm, which is more than the bed can move to compensate. Fortunately the probe Z-Offset is typically 2 to 4mm. However, a complicating factor is that each time the probe is homed Marlin re-defines the probe trigger point to be at zero height (Z=0). From there the bed must be moved up by the probe Z-Offset so that the nozzle touches a piece of paper on the bed. If, for example, the bed has been previously adjusted up 3mm and the probe Z-Offset is 2mm, the bed will need to be adjusted up to a total of 5mm (which is ok because it is less than the 6.5mm range). But next time, if the bed isn't adjusted down, the bed is at 5mm and the bed will again need to be adjusted up 2mm to 7mm (which is outside of the maximum bed adjustment range). So be aware.
From the Special Menu select 4 Point Level Menu:
Select each point A to D and adjust the Bed Leveling Screws so that the nozzle just brushes the paper.