Printer forgetting z-offset at start of new print

Falcounet

@feynman137 As you are using G30 S-1 and then using G92 Z4.1, your Z probe is useless and your are setting a random Z offset.
I would replace these 2 commands with G30.

Note that G30 can also do 2 speed probing (F parameter of M558), so you won't need to do it 2 times in the homing file.

Norder

@feynman137
The offset of the BLTouch is missing here.
G31 X0 Y0 Z4.1
The offset will probably come about between the distance of the nozzle and the actual measuring point of the BLTouch!?

Measure the offset of the BLTouch to the nozzle and enter the values in the G31 command line.
When determining the Z offset of the BLTouch, also make sure that the nozzle tip is clean and that not the slightest bit of filament residue is stuck there, as this would falsify the Z offset.

This is how you determine the offset of the probe (Click me / Duet3D Docs).

Google Translate
-- Original Text --

Hier fehlt der Offset des BLTouch.
G31 X0 Y0 Z4.1
Der Versatz wird vermutlich zwischen dem Abstand der Düse und des tatsächlichen Messpunktes des BLTouch zustande kommen !?

Messe den Offset des BLTouch zur Düse aus und trage die Werte in die G31 Befehlszeile ein.
Achte auch beim ermitteln des Z-Offsets des BLTouch darauf, das die Düsenspitze sauber ist und dort nicht die geringsten Filamentreste anhaften, dieses würde den Z-Offset verfälschen.

So ermittelt man den Offset der Sonde (Klick mich / Duet3D Docs).

Feynman137

I think I see what you mean. The height that the z probe records will always be 4.1mm however this is somewhat intended. The printer looks like the images below and the bl touch is basically being a limit switch. The plate moves up until the BL touch is triggered and then this is 4.1mm. Maybe the easiest thing is to tweak the 4.1mm in the config file, but this is not so ideal.

But I was thinking I could use the setting below to compensate this 4.1mm but it is forgotten with each new print.

Untitled 5.jpg Untitled 4.jpg

Falcounet

@feynman137 The Z offset is set using Z parameter of G31. When you use G30 S-1 you are actually asking the firmware to measure and report that offset.
To probe the bed, you have to use G30: https://docs.duet3d.com/User_manual/Reference/Gcodes#g30-single-z-probe

Feynman137

@falcounet

I will try this although I am confused as to why I cannot use G30 S-2 instead of G30 S-1.

But if I understand correctly when I issue G31 P500 Z2.6 for example at the instance the bl touch is triggered, the z axis height will be 2.6mm? Also is p500 correct for me?

Also I tried G31 P1000 Z4.3 and the bed moved down not up to meet the BL touch

Even G30 S-2 moves the plate down instead of up.

Falcounet

@feynman137 G31 shouldn't move the bed, G30 will and changing the Z probe settings with G31 will not change the axis direction.

If your Z axis move the wrong direction when using G30, you may probably need to fix the axis direction (S value of M569 for the Z driver). But the direction shouldn't have changed since using G30 S-1 ...

o_lampe

@Feynman137
@falcounet said in Printer forgetting z-offset at start of new print:

If your Z axis move the wrong direction when using G30, you may probably need to fix the axis direction (S value of M569 for the Z driver).

That is most unlikely the cause, since he can print several parts in a row.
I guess it's a false Z-endstop-definition? Z homing to min-endstop is the way to go.

Phaedrux

M558 F100				;adjust zprobing speed
G30 S-1        			; move Z down stopping at the endstop
G92 Z4.1				;set zaxis to z probe trigger height
G1 Z5 F100				;move build plate down slowly for second pass
M558 F10				;adjust zprobing speed to slow
G30 S-1					;zhoming second pass
G92 Z4.1				;set z coordinates

This is a very strange way to do Z homing. Why aren't you just using a G30?

Feynman137

@Phaedrux

What do you mean, I can just use G30 S-1?

Will my printer just use the offset in the config.g file?

Phaedrux

G30 S-1 is typically used to measure your probe offset.

G92 Z would be used to force a certain position, which kind of defeats to purpose of the probe.

Use a single G30 to probe, and you're good to go.

https://docs.duet3d.com/en/User_manual/Machine_configuration/Configuration_cartesian#homing-z

https://docs.duet3d.com/en/User_manual/Connecting_hardware/Z_probe_testing