When a print is paused, Z is reduced by 0.03/0.04 mm on restart

jens55

Got another weird thing I just noticed .... I am printing, I pause printing, when I continue with the print, Z is 0.03 mm lower than before. I have no clue where I would even start to look.
This is my pause,g file

; Pause macro file
G1 E-3 F2500 ; retract 3mm
G91 ; relative moves
G1 H2 Z3 F5000 ; raise nozzle 3mm
G90 ; absolute moves
G1 X305 Y85 F5000 ; move head out of the way

my resume.g file:

; Resume macro file
M116 ; make sure all temperatures are right

G1 R1 X0 Y0 Z2 F5000 ; go to 2mm above position of the last print move
G1 R1 X0 Y0 Z0 ; go back to the last print move
G1 E3 F3600 ; extrude 3mm of filament

I was under the impression that the nozzle position is automatically saved when a pause is called for and that this saved position is used to return the printhead to where it left off.
Is there any other macro that is run when the print resumes?
Am I screwing relative and absolute positioning somehow?

A typical sequence:
Power up printer, start print with first layer height of 0.20, pause, resume, Z now reports 0.16, pause, resume, Z now reports 0.13, pause, resume, z now reports 0.09.

Edit: I was tweaking babysteps to find the optimum print quality for the first layer. I am not sure if that affects things in any way.

moth4017

@jens55 hi just checked mine and its ok, what version of DWC/duet etc are you running
my macros

; pause.g
echo "pause"       ; called when a print from SD card is paused
M83                ; relative extruder moves
G1 E-2 F3600       ; retract  filament
G91                ; relative positioning
G1 Z5 F4000        ; lift Z by 5mm
G90                ; absolute positioning
G1 X250 Y260 F6000 ; go to X Y position

; resume.g
G1 R1 X0 Y0 Z5 F6000    ; go to 5mm above position of the last print move
G1 R1 X0 Y0 Z0          ; go back to the last print move
M83                     ; relative extruder moves
G1 E10 F3600            ; extrude 10mm of filament

jens55

@moth4017, I am running 3.5.0-beta.4

moth4017

@jens55 hi im running 3.5.0-rc1.try that version

deckingman

@jens55 Does the difference in Z height correspond with the amount of baby stepping used? Do you get the same error if you don't apply any baby stepping?

jens55

@deckingman, I have not tried without babystepping but will try that.
There seems to be no correlation with the amount of babystepping.
I will also try and see if this phenomena is limited to this printer or if a different printer does the same thing.

jens55

Did some more testing ..... on a different printer (3.5.0 - rc1), the issue does not exist.
The issue ocures even if I do not do any babystepping.
The issue still persists after upgrading to 3.5.0 - rc2
I compared the pause.g and resume.g files between the printer that does not show the issue and the printer that has the issue but could not determine any substantial difference
took the pause.g and resume.g files from the printer that works and installed them on the problem printer - the issue still persists
Tried yet another printer (3.5.0 - rc1) and the problem does not exist

The two working printers are single tool units, the printer with the issue is a tool changer (Jubilee) but no tool changes are involved

I have run out of ideas as to what to try next

OwenD

@jens55
Do you have any bed compensation applied?

moth4017

@jens55 do yours tools have different offsets ? if you change them all to the same offset just to do a test . does the issue go away?

jens55

@OwenD, yes, I have bed compensation enabled but I also have that enabled on the two printers that work.

jens55

@moth4017, yes, my tools have different offsets but there is no tool change involved. If it is an issue of tool offset, why would the height continue to reduce for every pause cycle?
I will see what happens when my z offsets are the same.

moth4017

@jens55 may be there is an undisclosed design feature (bug) that's taking of the offset from one of the tools , did you try making all the offsets the same ?

jens55

@moth4017, yes, just finished testing with all the same z offsets. Problem still exists.

moth4017

@jens55 can you post your config

jens55

@moth4017
config.g

moth4017

@jens55 in your config you are doing calculations instead of putting in the value, it may be a rounding issue , you could try putting in fixed values .

jens55

@moth4017, what in specific are you referring to?
Yes, I calculate motor current but that has no bearing on the issue.
I calculate z steps but that is an even number (no rounding) and besides, we are not talking actual height error (if the steps per mm are wrong) but we are talking what DWC 'thinks' is the z height.

jens55

I just looked at the object model during a pause and the Z height is correct. It would appear that the printer goes back to the right position and then reduces Z height somehow. This is confirmed by the DWC Z height display where, during the resume, z height goes to 0.2 (first layer height) and then drops down to 0.16.
It sure looks like there is some macro someplace that somehow changes the height on resume .... but where would this happen ... is there something that automatically runs after pause.g has executed ????

moth4017

@jens55 just a question are you doing the pause from DWC or in the slicer software ? eg pause at height x "do something" then resume?

jens55

How does resurrect.g fit in the big picture? I thought it only applies when there was a power outage?
The reason I bring this up is because the resurrect.g file contains this line:

G92 X266.207 Y126.771 Z-0.036 U0.000

and the z-0.036 seems very much like the error I am seeing.