Absolut zero height without Z end switch

Hi Everyone,

I am relative new to 3d printing and have some (actually a lot of) questions. But this time I would like to ask help regarding absolute zero height. Let me explain a bit:

I long term I would like to use bltouch with ABL. I will have more question regarding this later but at the moment I wanted to do the initial bed leveling manually using the "paper method". After doing some G28 and G29 according to the result I had to lift the bed a bit. But probably my springs under the bed loose now so I at the maximum height. I thought I will lower the whole bed for example approximately 2 mm and move also the absolute 0 height on my printer. But I cannot find any way to move the 0 height down. I'm using SKR 1.4 turbo with bltouch attached to the probe connector not in the z min connector. From this point the Z end switch does nothing. I assume there is an absolute zero height set somewhere as the bltouch can only measure relative height to the bed. Where can I set the whole nozzel's zero level? (I'm only able to find the Probe's Z offset which is do nothing in regarding this.)

Thank you in advance!

Edited 1 time(s). Last edit at 08/12/2020 07:19AM by newbie69.

I'm a little new also but have cnc experience. Can you explane how the z axis does the homing? Is there an endswitch and is it on top or bottom?

I'm using the probe for Z homing. No Z switch in the game...

You might be able to set a Z-max with an endstop at max and calculate maximum travel from there?

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http://www.marinusdebeer.nl/

with the bltouch connected to the Z min input, you should be able to adjust the Z zero with the probe Z offset (negative value)
If you set this in the configuration.h then you need to update the eeprom value by sending
M502
M500
to the printer

My bltouch is connected to the probe port not into the z min. However I think I finally found the solution. If anyone is interested:
G28: move the probe to the center of the bed
M211 S0: enable to move Z into negative
- adjust the Z height using the display menu
M851 Z0: set the new Z zero point
M500: store everything in EEPROM

I tried too much thing at a single night. I think this was the correct which solved my problem.
Thanks to all of you who took the time to think on my problem!