Absolute Z values not 0 at print surface after auto homing with CR-Touch

Question

I recently installed the CR-Touch onto my CR10-V3 printer. I updated my firmware to Marlin 2.1.2M and set my probe offsets and selected level bed which checked 81 points on the print bed and it said bed leveling was complete.

I tried printing something that I had already created G-code for from Prusa Slicer, and on the initial wipe and perimeter print the nozzle was way too high (maybe 10-15 mm off the print bed surface)

I searched for how to enable using the auto bed leveling mesh using Prusa slicer, and I found a couple of places mentioning adding M420 S1 to the G-code to enable using the auto bed leveling mesh, but even after adding that, my print did the same thing and during the wipe and perimeter print it was way too high.

Below is the start G-code that I'm using in Prusa Slicer

G90 ; use absolute coordinates
M83 ; extruder relative mode
M104 S150 ; set temporary nozzle temp to prevent oozing during homing
M140 S{first_layer_bed_temperature[0]} ; set final bed temp
G4 S30 ; allow partial nozzle warmup
G28 ; home all axis
M420 S1 ; Enable use auto bed leveling saved mesh
G1 Z50 F240
G1 X2.0 Y10 F3000
M104 S{first_layer_temperature[0]} ; set final nozzle temp
M190 S{first_layer_bed_temperature[0]} ; wait for bed temp to stabilize
M109 S{first_layer_temperature[0]} ; wait for nozzle temp to stabilize
G1 Z0.28 F240
G92 E0
G1 X2.0 Y140 E10 F1500 ; prime the nozzle
G1 X2.3 Y140 F5000
G92 E0
G1 X2.3 Y10 E10 F1200 ; prime the nozzle
G92 E0

If I'm understanding the last part of that G-code, it should be 0.28 mm above the print bed when it does its nozzle wipe, but it's 10 mm or more off the bed when it does that.

I did some additional testing this morning, and the problem seems to be the z-values after auto homing. I have a z-probe offset entered of -2.122 mm that I got using the z-probe offset wizard in the Marlin firmware, and that offset visually seems reasonable for where the probe triggers vs the nozzle height.

After auto homing all axis, if I manually change the z-axis to be 0.28 mm, then the nozzle is still about 7 mm above the print bed which is where my prints are starting off.

If I manually deploy the touch sensor and lower the print head, the touch sensor engages with the print surface at around a z position of -5 mm, and then with the z-probe offset of -2.112 mm it's about 7 mm too high.

Where is this extra height coming from? I've checked and rechecked the z-probe offset, and like I said, the values seem reasonable, but I'm not sure where this extra height is coming from.

Answer 1

I have no idea what happened the first time I initialized everything, but I started over from the beginning and ran the Initialize EEPROM command from the UI, and then saved the settings, and then went to the probe offsets and reset my probe offsets to exactly what they were before, but now after auto homing the absolute Z values look accurate and if I manually move the Z axis to 0 it is right at that 0.1 mm height of a sheet of paper.

The first time I initialized the EEPROM I ran auto home immediately after and I was getting an error on the main page ERR: too far and maybe in the process of trying to fix that I messed something else up, but it appears that everything is working how it should now.

Answer 2

Although I cannot be sure, I suspect that your bed-leveling is working fine.

An auto-bed-leveling-sensor only takes care of relative bed leveling. That means that you have to manually add a Z-offset in the printer menu. Do this by running the auto-leveling, then auto homing and then adjusting the Z-value by moving the Z-axis in the menu until the head barely touches the bed. Note the value and fill this in for the Z-offset value in the configuration menu of the printer.