How can I change the starting z-height when performing manual bed leveling?

[JHP]

I want to change the starting position of the Z height of the 3D printer head when performing manual bed leveling.

I want to add a MDF board, approximately 2cm thick, underneath the print bed of my 3D printer in order to level the bed.

Adding the MDF board will increase the height of the bed by approximately 2cm.

The issue is that when I perform manual bed leveling, it automatically moves to a lower position as shown in the picture below.

I want to be able to start manual bed leveling at a position 3cm higher than the current position, as shown in the picture below.

If anyone knows how to do this, please help me.

[Mxbrnr]

Starting z-height for manual bed levelling is preset by the firmware code. To change it, you would have to custom edit that code.

[JHP]

Thank you for showing interest in my topic.

I attempted to modify some variables in the firmware code, but it had no effect.

Can you help me verify it together?

1. I tried changing the “DEFAULT_LEVELING_HEIGHT” value to 50 in the Snapmaker/Snapmaker2-Controller/Marlin/Configuration.h file (line 1238).
   This variable is used in the “reset_bed_level()” function in the …/Marlin/src/features/bedlevel.cpp file (line 148).
   
   
   
   
   

This had no effect.

2. I tried changing the “MANUAL_PROBE_START_Z” value to 50 in the Snapmaker/Snapmaker2-Controller/Marlin/Configuration.h file (line 808).
   This variable is used in the “_manual_goto_xy()” function in the …/Marlin/src/features/bedlevel.cpp file (line 247).
   
   
   
   
   

This had no effect.

3. I tried changing the “z_offset” value to 50 in the …/Marlin/src/feature/bedlevel/mbl/mesh_bed_leveling.cpp (line 48).
   
   

This had no effect.

4. I tried changing the last parameter of “onMeshUpdate()” value 0 to 50 in the …/Marlin/src/feature/bedlevel/mbl/mesh_bed_leveling.cpp (line 53).
   
   

This had no effect.

What else should I try to change?

[xchrisd]

Automatic bed level, simply try it, i had the cnc bed under my heated bed for more than one year.

If you want to be sure that the nozzle not touching the bed (what not really happened to me) you could simply trigger the bed sensor once and the travel speed of the z axis would decrease to slow speed.
Simply try it, i had the cnc bed under my heated bed for more than one year.

Oh, i am sorry, didnt read the manual bed leveling.

[Rwide]

I assume the Z-axis limit switch is a probe on the toolhead?

What if you just put the MDF board on the buildplate, raise the toolhead above the board, home your z-axis and then perform the manual bed leveling. Doesn’t that work?