Auto Z offset mod for Snapmaker 2.0

Uses a limit switch to automatically set the z offset, making autoleveling fully automatic with no manual intervention.
This is designed for Snapmaker 2.0 A350 3d printers, but can be modified to work with other printers.

Hardware:
x1: KW12-3 Micro Limit Switch
AliExpress: https://tinyurl.com/4h9t37vt
x2 M2x12 bolts and nuts


The Z offset has to be set up once and must be reset if you change the printbed.
To set the z offset

(Clean the nozzle first if you have a nozzle cleaner)
1. Set absolute Positioning (G90)
2. Move the nozzle over the limit switch (G0 X339)
3. Move it down until it triggers the switch G38.2 F100 Z0
4. Record the Z height. (M114) - switch_Z
5. Move the nozzle over the center of the bed G0 X160 Y176
6. Set the Z offset the way you normally do
7. Record the Z height (M114) - bed_Z
8. Calculate the Reference Height (switch_Z - bed_Z)

To run autoleveling, run these G-code commands
M190 S{bed temp} ; Heat Bed & Wait
G1029 P{Grid Size}