Z offset resets on every print or Homing and start gcode asking

[peter247]

@eengineer I'm a little lost what you are asking ?.

You have a bltouch which should set the same z offset with a differing bed height etc , so if you rehome you should get the same offset from the nozzle to the bed.
BUT you will find that using baby-stepping you can 't go lower that zero Z.

[EEngineer]

@fcwilt
The Z-Offset between the nozzle and the bed which I would like to set with a BLtouch

@peter247
Sorry for the misunderstanding.
Yes I have, and I can set it. Then I re-home, or start a print and the Z-offset changes back to some other value. Like it got a new Z0, thats why I cant babystep down more I think. So when I start a new print it only prints in the air well above the bed and in DWC it says its on Z0.3 on first layer.

[peter247]

@eengineer and the Z-offset changes back to some other value

Does it show a different value on the screen or are you guessing ?

in the air well above the bed and in DWC it says its on Z0.3 on first layer.

Have you tried a homing paper test ?

Which is in the centre of the bed , home and baby step down until a bit of paper grips the nozzle .
if it doesn't grip the paper than you need the change the offset in G31

[EEngineer]

@peter247

It doesn't show value but I guess if after a G30 probing it stays well above the bed then the Z0 has changed.

That's what I am doing in the Z-Offset macro yes. Babystepping down. Then it saves the Z0 until re-home or print start.

[peter247]

@eengineer What would do and how I do mine is :

Change your G31 P25 X-29.75 Y-14.50 Z2.2 and reduces the Z offset by say 0.5mm ( or more ) Z 1.7 and babystep down until it grips the paper , which it should just touch at 0.1mm and grip hard at zero.
Now if it grips the paper at 0.3mm just increase Z offset value by 0.2mm and try again.

YOU NEED TO LOWER THE G31 Z value and reboot.

[EEngineer]

@peter247
I have tried so many ways now. In the beginning it was Z0.0 in G31.
I have to babystep down, usually it grips in -2.1.
But I will have a try again..

[peter247]

@eengineer

Have you any adjustment on the bltouch to move it down ?

Wow -2.1mm that must mean that the nozzle is almost hitting the bed when the probe retracts ?

[EEngineer]

@peter247
The Z offset between the nozzle and BLTouch is at about 3mm

I don't know if it means this, but it is not near to hit the bed when it retracts

[peter247]

@eengineer said in Z offset resets on every print or Homing and start gcode asking:

The Z offset between the nozzle and BLTouch is at about 3mm

Not sure what you mean , is that on the screen or the distance between the nozzle and the bed which you have measured AND 3mm when ?

just thinking I'm wrong the probe to too few down !!!!

[EEngineer]

@peter247
About 3mm Between the tip of the nozzle and the tip of the BLtouch. Thats what you define in G31, isn't it? Thats why it is off with X-29.75 and Y-14.5. Z-probe position from the nozzle's point of view.

[fcwilt]

@eengineer said in Z offset resets on every print or Homing and start gcode asking:

@peter247
The Z offset between the nozzle and BLTouch is at about 3mm

Are you referring to some distance between the nozzle and the BLTouch?

If so, why are you concerned with that?

The only thing of importance is the BLTouch Z Trigger Height setting in G31.

How are you determining that value?

Frederick

[peter247]

@eengineer

if you set it to -2mm so it grip the paper how close is it to hitting the retracted probe ?

I can see now your bltouch is closer to the bed when it touches than mine, but your -2.1mm says not.

something is wrong I can't work it out !!!

[EEngineer]

@fcwilt

Now I set my Z Trigger height in G31 according to this:
https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe#Section_Calibrate_the_Z_probe_trigger_height

After that my print start has began on the right Z height.. Thanks for the advices. As I see now, that was my problem..

My other question is, what do you think, what should I include in my start or maybe end g-code on an idex.
Is there something special for RRF that I should include in these?

[fcwilt]

@eengineer said in Z offset resets on every print or Homing and start gcode asking:

@fcwilt

My other question is, what do you think, what should I include in my start or maybe end g-code on an idex.
Is there something special for RRF that I should include in these?

I have no idea as I do not have a printer like that.

But someone here is sure to have ideas.

Frederick

[EEngineer]

@fcwilt
I think I read somewhere that I should use relative extrusion. is it right? Then I should include in the start g-code

[peter247]

@eengineer it should be in your config.g file

G90 ; send absolute coordinates.
M83 ; but relative extruder moves.

but you have to tell the slicer to use relative extruder too.

in cura it is in special modes

[fcwilt]

@eengineer said in Z offset resets on every print or Homing and start gcode asking:

@fcwilt
I think I read somewhere that I should use relative extrusion. is it right? Then I should include in the start g-code

I make use of the slicer feature where you can enter you own code for print start and print end.

I only enter M98 P"print_being.g" and M98 P"print_end.g"

Everything I want to do is in those files BUT the slicer generates a bit of it's own code and the relationship of that code to the call to my code varies with the slicer and the slicer configuration.

Here is some relevant info:

; S3D inserts the following before the call to print_beg.g
;G90                    ; absolute XYZ moves
;M83                    ; relative E   moves
;M106 S0                ; fan on to 0 (correct way to do fan off)
;M140 S60		; set bed      temp but don't wait
;M104 S190 T0		; set extruder temp but don't wait
;M98 P"print_begin.g"

; Cura (Repetier flavor - no temps) inserts the following around the call to print_beg.g

;M109 S0                        ; set extruder temp and wait (no wait with S0)
;M82                            ; absolute E moves
;M98 P"print_begin.g"
;G92 E0                         ; set E position
;G92 E0                         ; set E position again (have no idea why)
;G1 F1800 E-1                   ; do initial retract

; PrusaSlicer (RepRapflavor - no temps) inserts the following around the call to print_beg.g
;M107                           ; fan off (should be M106 S0)
;M98 P"print_begin.g"
;G21                            ; set units to millimeters
;G90                            ; absolute XYZ moves
;M83                            ; relative E moves

[EEngineer]

@fcwilt

This is very convenient, thank you for the tip.

I had a few succesful print since I made the Z-offset correctly.