Z trigger height

FelixH

Hi all,

Probably a very silly question, but I am in doubt right now, so please bear with me...

On my Marlin Machines, I use the following start G-Code to set the Z-Probe Offset:

M851 Z-0.32 ; set z probe offset

On my Duet machines, I have the value hard-coded to the config.g file.

My question is: can I also set the probe offset on the start G-Code also on the Duet Machines? I am assuming that much, but I just want to be sure...

BTW: I know that on Duet is called Trigger Height and is calculated differently...

Veti

yes you can issue the G31 command just like the M851 in marlin

FelixH

@Veti thanks for the confirmation. If I add it on the initial Gcode, I can adjust it more rapidly, without having to reboot the board.

Veti

@FelixH

I can adjust it more rapidly

yes it takes effect without rebooting, but you need to do a new home

Phaedrux

Perhaps using baby stepping would be more appropriate, then you wouldn't need to rehome.

https://duet3d.dozuki.com/Wiki/Gcode#Section_M290_Baby_stepping

fcwilt

@FelixH said in Z trigger height:

@Veti thanks for the confirmation. If I add it on the initial Gcode, I can adjust it more rapidly, without having to reboot the board.

I have a pair of macros (print_begin.g and print_end.g) that are called (using M98) by settings in the slicers I use.

Two of the things that happen in print_begin.g are a call to a macro configprobe.g and then a call to a macro probez.g

The Z trigger height setting happens in configprobe.g using G31.

So if I need to change it, I just edit the file and then subsequent prints use the new settings.

No need to re-boot, no need to home.

Frederick

FelixH

Thank you all for your inputs.

FelixH

Is there any kind of trick on finding out the correct trigger height? Any time I have to re-calibrate is like a trip to hell. After following this guide:

https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe

I get, for example, a trigger height of 1.50mm. I set it on the config.g file and I do a test. The nozzle is way too far from the bed and I try to use Babystepping to get it closer. The Babystepping shows me a -0.15 (for example)... now what? Should I correct the config.g file and set the trigger height to 1.35 (1.5-0.15) ??

Phaedrux

@FelixH said in Z trigger height:

Should I correct the config.g file and set the trigger height to 1.35 (1.5-0.15) ??

If it's consistent, yes.

If you do the G30 S-1 test multiple times over does it give a consistent result? Are you also homing in that same spot?

FelixH

@Phaedrux yes it is consistent and also yes, it homes to the same spot.

fcwilt

@FelixH said in Z trigger height:

I get, for example, a trigger height of 1.50mm. I set it on the config.g file and I do a test. The nozzle is way too far from the bed and I try to use Babystepping to get it closer. The Babystepping shows me a -0.15 (for example)... now what? Should I correct the config.g file and set the trigger height to 1.35 (1.5-0.15) ??

To get the nozzle to be closer to the bed you increase trigger height.

In your example you decreased it.

The trigger height determines how far the nozzle must move to reach Z=0. If the current value of the trigger height is leaving the nozzle above the bed then the nozzle did not move far enough. To get the nozzle to move more you increase the trigger height.

Frederick

FelixH

@fcwilt

To get the nozzle to be closer to the bed you increase trigger height.

In your example you decreased it.

This is exactly what puzzles me every time. The pop up on the Panel Due shows a minus value an yet, it’s the opposite...

fcwilt

@FelixH said in Z trigger height:

This is exactly what puzzles me every time. The pop up on the Panel Due shows a minus value an yet, it’s the opposite...

I know it can be confusing.

When the probe is triggered the trigger height setting (assume 2 mm) says to the firmware "hey the nozzle is now 2mm above the bed". The firmware says to itself "ok so to move the nozzle to Z=0 I must move closer to the bed by 2mm"

When you adjust baby stepping to a negative value you are saying to the firmware "hey you need to move closer to the bed".

And as you can see to move closer to the bed requires a larger trigger height.

Frederick