Bl-touch and distance printing nozzle

sko

(I couldn't edit my previous post b/c it was tagged as spam!?)

I compared the manually determined trigger height to the one reported by G30 S-1 and it is always off by ~.45
Actual trigger height at the point where Z is homed (and the probe is above the bed) as said is ~1.4mm If I run a G30 S-1 at the same position it reports ~1.8-1.9mm trigger height...

jens55

Did you run a new bed mesh once you had adjusted your z zero ?
I don't know this for sure but it sounds like the additional offset is because you applied bed mesh compensation.

sko

As soon as I ran a bed mesh compensation, the error was introduced into the height map and the nozzle was ~0.4mm above the bed when moving to "Z=0"

I now reverted to using G30 S-3 directly next to the Z-endstop. This fixes the mysterious ~.4mm error that was consistently introduced when using G30 and a fixed offset in the config.g. So I removed all probe offsets from the config.g and now set the offset during Z-homing:

; homez.g
; called to home the Z axis
M561					; cancel all bed mesh compensations
M558 P1 C"!zprobe.in" H15 F300		; increase dive height to prevent crashing into a tilted bed

; probe and adjust the bed tilt
G90	
G30 P0 X50 Y165 Z-99999 ; probe near a leadscrew
G30 P1 X350 Y165 Z-99999 S2 ; probe near a leadscrew

M558 P1 C"!zprobe.in" H5		; reduce dive height after adjusting the bed

; move over endswitch to set Z=0
G1 X341 Y310 F18000
G1 H1 Z-350 F600 ; move quickly to Z axis endstop and stop there (first pass)
G1 Z5 F1200       ; move up a few mm
G1 H1 Z-6 F300   ; move slowly to Z axis endstop once more (second pass)
G92 Z0 			; set Z=0
G1 Z15 F1200   ; lift printhead

; calibrate probe trigger distance
G1 X341 Y313 F18000	; move directly next to the switch to calibrate the probe
G30 S-3				; set probe trigger height
G1 Z15 F1200		; lift printhead

G1 X0 Y330 Z20 F18000				; move printhead to the back

afterwards I can run bed mesh compensation and am getting plausible results (with an error of ~0.015-0.02mm over multiple mesh compensation runs) and the compensation is properly working. I.e. I can move to any point on the bed and when moving the Z-axis to 0 the nozzle actually touches the bed, even if I deliberately introduce an error somewhere.

jens55

I am now officially lost ....
In your homez.g macro you are adjusting bed tilt but you only run the tilt routine once. Normally this is a successive approximation so it would make more sense to run this several times (the tilt compensation)
Then you run close to where the limit switch is located and set z=0. Never mind the fact that ideally z should be set to zero when it is in the middle of the bed .... you are now using the z limit switch and not the probe.
You then run the probe and over-ride the previous z=0 setting which was set with the end limit switch rather than the probe.

There is a good possibility that I do not completely understand what is happening here but it looks to me like the probe triggering point is different from the endstop trigger point and you are seeing weirdness because of that.

I think I would like to bow out from this discussion as I feel I am over my head.

sko

@jens55 said in Bl-touch and distance printing nozzle:

I am now officially lost ....
In your homez.g macro you are adjusting bed tilt but you only run the tilt routine once. Normally this is a successive approximation so it would make more sense to run this several times (the tilt compensation)

I wasn't aware of that. The reported adjustment is usually <0.2mm, but I will try to rewrite it to repeat until the deviation is even lower.

Then you run close to where the limit switch is located and set z=0. Never mind the fact that ideally z should be set to zero when it is in the middle of the bed .... you are now using the z limit switch and not the probe.

Z=0 is set at the position where the limit switch is triggered. I confirmed this several times by checking the nozzle height after this step.

You then run the probe and over-ride the previous z=0 setting which was set with the end limit switch rather than the probe.

G30 S-3 doesn't set the Z=0 value but only the trigger height:
G30 S-3 ; Probe the bed and set the Z probe trigger height to the height it stopped at

There is a good possibility that I do not completely understand what is happening here but it looks to me like the probe triggering point is different from the endstop trigger point and you are seeing weirdness because of that.

I am aware that the endstop trigger is different from the probe trigger height.
My problem was, that when using G30 to home Z using the probe, there was an offset of ~0.4mm added somewhere. This led to Z=0 being off by the same value when I tried to home Z by only using the probe and the trigger distance defined via G31 in config.g

Touchthebitum

I followed this process and it seems to work :
-put z=0.0 in config.g G31 line

homing all axes
G30 (be careful and be ready to press emergency button)
manually jog nozzle to touch the bed
G92 Z0
manually jog 10mm z axes away from nozzle
G30 S-1 (2 times)
insert the z value in the G31 line
Start mesh process from the PanelDue

I did it 2 times and if you want to modify the z, you have to redo the all process (in my case)

Touchthebitum

@jens55
Thanks I have to control. I have now layers problems and it could be this step/mm that causes it.
But 80 steps/mm is very low...

jens55

It all depends on your mechanics .... it works for me but there are many reasons why it might not be right for you. The appropriate thing is to measure things and adjust until the Duet and real life agree

Touchthebitum

@jens55
Ok, I'll check

Phaedrux

This thread is very confusing to follow because there are 2 people with problems posting in the same thread.

Best way to get accurate and timely help on a problem is to post a good description of the problem and include all of your config files. RRF is configured with gcode, so showing what gcode you are using is critical to helping others understand what's actually happening with the printer.

@Touchthebitum @sko if you want some more help getting your z offset correct, start new threads and include your files. It's usually a fairly simple fix to methodology.