How to: storing the Z-offset automatically without using M500

ComedianTF2

If for whatever reason you want to store the Z-offset outside of the config.g file (in this example in a file named config_probe.g), here is the method I've found out to work quite well.

This method works for RepRapFirmware 3.4 and up, as we need to use the ability to write to a file using the echo command. It has been tested on 3.4.1

For more info, see https://docs.duet3d.com/User_manual/Reference/Gcode_meta_commands#echo-command

The macro also allows you to automatically compensate for using of a known thickness shim, using the var probing_tool setting at the start of the macro.

Z-offset macro:

var probing_tool = 0.000
; This allows you to compensate for whatever tool you use to measure the nozzle distance.
; It is set to 0.000 by default, you can set this to the thickness of the tool or paper you use for the Z-offset calibration
; A sheet of paper is on average 0.05 to 0.10mm thick.

M291 S3 R"Heating up nozzle" P"Wait for the nozzle to reach printing temperatures"
M568 P0 S215		; set tool 0 (primary hotend) temperature to 215c
T0			; select tool 0 (primary hotend)
M116 P0 H5		; wait for temperature to reach within 5c of set temperature

M300 S666 P666               ; beep
M291 S3 R"Setting the Z-offset Height" P"Press OK to continue, or CANCEL to abort"
G28                          ; home all
G29 S2                       ; cancel mesh bed compensation
M290 R0 S0                   ; cancel baby stepping
G90                          ; absolute movements

G1 Z10
G1 X100 Y100 F1800
G4 P0

M300 S1111 P666              ; beep
M564 H1 S0                   ; ignore axis limits
M291 S2 R"Test Z Probe Trigger Height - Step 1" P"Place a paper sheet under the nozzle and raise the bed until slight friction can be noticed" Z1 ;

G92 Z0                       ; the nozzle should now be just touching the bed so set the logical Z position to match the physical Z position
M300 S666 P666               ; beep
G1 Z8 F300                   ; insure Z position will allow for probing
G4 P0						 ; wait for the movement to stop

M291 S2 R"Test Z Probe Trigger Height - Step 2" P"Please remove the paper sheet and wait for the bed-probing to begin" ;
G30 S-1                      ; probe the bed and report the Z probe trigger height
M564 S1 H1                   ; respect axis limits

;M291 S2 R"Test Z Probe Trigger Height - Step 3" P"Copy the reported height value on the G-Code console and paste it into the config_probe.g file"

var Z_auto_offset = {sensors.probes[0].lastStopHeight+var.probing_tool} ; math to calculate the BLTouch offset
echo >"0:/sys/config_probe.g" "G31 Z"^{var.Z_auto_offset}				; write the Z-offset to the config_probe.g file

echo "the Z-offset has been stored in the config_probe.g file. The Z-offset is", var.Z_auto_offset, "mm"

G4 P0						 ; wait for the movement to stop
G1 Z10 F300                  ; Lift up the nozzle again so it's not pressed against the bed surface

config_probe.g :

G31 Z1.5

It's a fairly simple macro, but if there are any questions let me know

Trojan3D

Hello,
Any chance i can save the Z-offset directly in the "Config.override" file without deleting all the other settings instead of creating a new one?
Thanks a lot for your time.

ComedianTF2

@Trojan3D If you change it to be >> instead of > on the echo, it adds data to the file instead of overwriting it

So in your case it would be:
echo >>"0:/sys/config-override.g" "G31 Z"^{var.Z_auto_offset} ; write the Z-offset to the config-override.g file

This adds the value to the last line of the config-override.g, however you will see it become quite a mess over time, as the echo >> only adds another line

So after doing it ten times, you it would have the G31 Z value added ten times in a row, with the bottom one being the value you're trying to have.

That's why it's generating a separate file called config_probe.g in this example, and then you can load the Z-offset using a M98 P"config_probe.g" in your config.g and homing files

Trojan3D

@ComedianTF2 That's great, thank you very much for your help!
New to duet and trying to figure out what's what here in my new Prusa Bear with Duet mini.
All the best and thank you again.

bluenavy

@ComedianTF2 Hi, thanks for this macro, it's very handy. I've tried to use it but i think I'm having a problem with calling the config_probe.g file into config.g. I've used:
G31 K1 P500 X-28.2 Y-18.1 ; set Z probe trigger value offset
M98 P"0:/sys/config_probe.g" ; z probe trigger height

When I try to print, there isn't any z-offset. Am i doing this properly?

Thanks

ComedianTF2

@bluenavy I have it similar to you, so check that the config_probe.g is populated properly

G31 P500 X-22.5 Y38.9	; BLTouch X and Y offset
M98 P"config_probe.g"	; Load the Z-offset from the config_probe.g file

Then the config_probe.g file is this:

G31 Z2.688

And homing files also have the Z-offset loaded in there

; homeall.g
; called to home all axes
M98 P"config_probe.g"	; Load BLTouch probe settings
M280 P0 S60 I1		; clear any probe errors
G29 S2                      	; cancel mesh bed compensation
G91                    		; relative positioning

M913 X50 			; X axis 50% power

G1 H2 Z5 F200          	; lift Z relative to current position
G1 H1 X{(move.axes[0].max+5)*-1} Y{move.axes[1].max+5} F3000  	; move quickly to X and Y axis endstops and stop there (first pass)
G1 H2 X5 Y-5 F600      	; go back a few mm
G1 H1 X{(move.axes[0].max+5)*-1} Y{move.axes[1].max+5} F600  	; move slowly to X and Y axis endstops once more (second pass)

M913 X100 			; X axis 100% power

G90                    		; absolute positioning
G1 X{move.axes[0].min+2} Y{move.axes[1].min+2} F6000 		; move to front left

G1 F600				; reduce speed
G30                    		; home Z by probing the bed
G29 S1				; load heightmap

bluenavy

@ComedianTF2 Thanks!