I have an Ender 3 Pro which I recently added an SKR Mini E3 v2.0 with Marlin and BLTouch. I have run into an odd issue where roughly the first 10 mm of the print are compressed into ~7 mm of Z height. I don't think its mechanical based on the following process.
- Power on the printer, Auto Home.
- Move the print head to the middle of the bed ~1 mm off the print surface (move the nozzle down until it touches, then back of 1 mm)
- Measure the nozzle height relative to the print bed, command a 10 mm Z move, measure the Z nozzle height it's 10 mm higher.
- Level the bed with the BLTouch (The Z offset is correct and 0 mm is basically at the print surface)
- Repeat the process above, start with the nozzle 1 mm off the bed, command a 10 mm move. The measured height of the nozzle is now only 7.5 mm higher than it was.
- Anything I try after this (rehoming, running bed leveling again) still results in a 7.5 mm move when a 10 mm is commanded. It's only the 10 mm closest to the bed, a second 10 mm postive move results in 10 mm delta to the nozzle height.
All prints consistently have the same compression of the first layers.
Two other pieces of information that seem like they are relevant, the Z zero when homed is about 2.5 mm lower than when I run bed leveling. ENABLE_LEVELING_FADE_HEIGHT is set to 10.0 mm. Those two numbers combined seem really suspicious to me, but its not clear to me what to change if that is the problem.
This calibration block should be 50 mm high, it's 47 mm high and the 3 mm are lost in the first 25mm step:
