Trouble understanding how to set up Z-probe offset

Brekel

Hi,

As a delta owner coming from Smoothieware I'm having some trouble wrapping my head around setting up my Z-probe and calibration.
So I was hoping for some help from the experts here.

My machine has magnetic arms which I use to swap between my effector with Z-probe and another effector with my hotend.
(to keep the hotend light and compact)

I can succesfully run auto calibration and mesh bed compensation however don't understand how/where to put my probe/hotend Z-offset.

My Z-probe is configured as:
M558 P5 X0 Y0 Z0 H40 F300 T2000 R0
G31 X0 Y0 Z0 P500

When I manually move until the Z-probe is triggered Z=20.70
When I swap to my effector with hotend and manually place it to touch the bed my Z is 18.73

In smoothieware I normally place the effector to touch the bed then do:
M306 Z0
M500

Which stores the offset in an override file as:
M206 Zn.n ; (n.n is measured offset)

I'm trying to wrap my head around how/what to do this on my Duet Wifi (which I like much more!)
It seems G92 Z0 defines the current Z as Z=0, however this does not seem persistent after homing or a power cycle.
Or should I manually calculate a rough offset and place it somewhere in th config/bed file (where?), and then rely on baby stepping for fine tuning?

Probably a simple thing but I'm just a bit confused for the best solution, any help?

dc42

It is indeed the G92 Z parameter that defines the Z probe offset. However, when you run M500, the current Z probe offset parameters are amongst those written to config-override.g. So your config-override.g file may be overriding the value that you put in config.g. So you can send a G31 command with the parameters you want, then send M500 to save them.

config-override.g is only used if you have the command M501 (or M98 Pconfig-override.g) in your config.g file.

HTH David

Brekel

Ok looks like I've got it to work by adjusting the G31 Z in config.g in a few iterations.
Never got that G92 Z0 to work always seemed to be reset after doing a home.
But it may be me being stupid as a newbie

Really liking the board, firmware and web interface so far, you've done an incredible job!

dc42

I'm glad you like it!

Sending G92 Z0 and homing Z are two different ways of defining where Z=0 is. So homing Z will cancel the effect of previously running G92 Z0.

retroglyph

I am sorry that I also do not understand this. I, too, am coming from smoothie. In the past, I would do a g32 with a microswitch. It would check for bed level at some unknown height above the bed. Then I would remove the microswitch, lower the nozzle til just touching the paper, G92 Z0 and M500. boom.

With this, I have been trying for over an hour. I did the autocalibration with the microswitch on. And then I removed the microswitch. Z0 results in the nozzle sitting 18.64mm above the bed.

I tried to follow this:
https://www.duet3d.com/wiki/Calibrating_a_delta_printer

I use M208 S1 Z-20 to allow the nozzle to move down.
I use G Z-18.64 to lower nozzle to piece of paper (that works)

then I have tried changing this in the config:
G31 P600 X11 Y0 Z0 ; Set Z probe trigger value, offset and trigger height
to
G31 P600 X11 Y0 Z18.64 ; Set Z probe trigger value, offset and trigger height

but still when Z0 the nozzle is at 18.64mm above bed.

I've deleted the last few lines from the config-override and then lowered nozzle to bed, used g92 Z0 then M500, reopened config-override:
G31 T1 P500 X0.0 Y0.0 Z0.70
G31 T3 P500 X0.0 Y0.0 Z0.70
G31 T4 P600 X11.0 Y0.0 Z18.64

How do I convince my machine that it needs to be 18.64mm lower?

I decided to go into config-override and I changed this line:
M665 L304.170 R151.502 H241.959 B125.0 X0.025 Y0.027 Z0.000 ;
to
M665 L304.170 R151.502 H260.599 B125.0 X0.025 Y0.027 Z0.000 ;new-H260.599 old-H241.959

basically, I told the machine that it was 18.64mm taller than it calibrated at. That seems to work. but what is the correct way?

dc42

It sounds to me that you adjusted the G31 Z parameter to 18.64 after you had run auto calibration, instead of before. The firmware needs to know the Z probe trigger height during probing.

With a removable probe, your approach of adjusting the homes height afterwards is equally valid.