G28 / G29 / G32 - confused when using 2 independent Z-Axis

kuhnikuehnast

Hi!
I am a littlebit confused at the moment and hope you can help me.
I use 2 independent Z- axis (Stepper Driver 2 and 4) and want adjust a possible Z-axis difference in the calibration procedure. (The printer is a "Prusa-Style-Type")

I now wanted to do it like this:

G28 ; home all axis
G32 S2 ; adjust the 2 Z-Stepper to be the same height
G29 ; perform a mesh bed levelling
printing.

But if I perform it like this, the bed is always completely below the surface. None of the points are at 0. So I tried to perform a "second Z-Home" (G28 Z) bewteen 2 and 3. The effect was, that then the bed isn't any more flat on the points defined in G32... ? So what am I doing wrong?

Here the "relevant" G-Code:
config.g:
M584 X0 Y1 Z4:2 E3 ; Define drive mapping- Z= driver number 2 and 4.
M671 X-77:297 Y10:10 S3 ; Set position of the leadscrews
G31 P25 X+26.9 Y5.935 Z0.905 ; Set Z probe trigger value, offset and trigger height
M557 X20:200 Y20:200 S45 ; Define mesh grid

home.z:
G91 ; relative positioning
G1 Z5 F6000 S2 ; lift Z relative to current position
G90 ; absolute positioning
G1 X110 Y110 F6000 ; go to first probe point
G30 ; home Z by probing the bed

bed.g:
M561 ; clear any bed transform
M401 ; deploy mechanical Z probe
G30 P0 X20 Y110 H0 Z-99999
G30 P1 X200 Y110 H0 Z-99999 S2
M402 ; retract mechanical Z probe

Phaedrux

What firmware version are you using? Also I don't see a M554 command. What type of z Probe are you using?

kuhnikuehnast

I only copied the relevant files for probing. I am using a BLTouch probe.

kuhnikuehnast

@phaedrux said in G28 / G29 / G32 - confused when using 2 independent Z-Axis:

What firmware version are you using? Also I don't see a M554 command. What type of z Probe are you using?

You don't need a M554 command if you are connecting by M552...?

Phaedrux

@kuhnikuehnast I'm sorry, I meant M558 for probe configuration.

Phaedrux

Also, the reason I asked what firmware version is that there was a bug that could cause the mesh offset to be applied incorrectly leading to off first layers such as you describe.

kuhnikuehnast

I am on the actual firmware (2.0(RTOS) (2018-06-05b3))

The M558 is:
M558 P9 H5 F180 T15000 ; Set Z probe type/mode 9. H=Dive Height. F=Speed the bed moves

Phaedrux

Try firmware 2.01 veta 2.

https://forum.duet3d.com/topic/6070/new-firmware-2-01-beta-2-available

Then rerun your bed leveling and probe offset measurements and see if your issue is resolved. Part of the problem was that M561 was not clearing the bed transformation as expected.

Phaedrux

If that doesn't help, try adding this to the start of your print gcode

G29 S2 			; Disable bed compensation.
G29 S2 			; Disable compensation again.
G28 Z			; Home Z
G29 S1 			; Load heightmap.csv and enable compensation.

kuhnikuehnast

But am I right with this procedure:

G28
G32
G29 ?

Phaedrux

Yes I think so. You appear to be following the guidelines here: https://duet3d.dozuki.com/Wiki/Bed_levelling_using_multiple_independent_Z_motors

There should be a final g28 z before starting a print to make sure you know where z0 is so that first layer height is accurate.