Mesh Grid wrong coordinates

[Queevix]

Hey everyone,

So I seem to behaving another strange little problem.
The printer works, as I can home all axes as expected, and I also managed to make my first print, but I can't get the Mesh bed levelling to work as I want it to.

This is the code I'm using for the moment on my Z-probe settings:
; Z-Probe
M558 P5 C"!io3.in" H5 F120 T6000 ; set Z probe type to modulated and the dive height + speeds
G31 P500 X48 Y65 Z0.35 ; set Z probe trigger value, offset and trigger height
M557 X50:450 Y65:450 S80:77 ; define mesh grid

Now, as I run the mesh bed compensation with either G32 or G29, the printhead for its first measurement moves to X0Y0, and probes there, which is problematic, as the bed is not under the probe at this coordinate.
Over the last week, I have used many different coordinates for both the X and the Y position, as well as for the point spacing. I always get this same result.

Anyone have any idea what I'm doing wrong?

[chrishamm]

@queevix In your G31 line you specify a probe offset. Are you sure it is correct? RRF adds the probe offset to the requested position when you run G29.

[Queevix]

@chrishamm

I had not considered this. I use this offset (X48 Y65) as is the position where I want the probe to home the Z-axis. And that's how it seems to work.

Now, thanks to your advice I wrote it like this:
; Z-Probe
M558 P5 C"!io3.in" H5 F120 T6000 ; set Z probe type to modulated and the dive height + speeds
G31 P500 X48 Y65 Z0.35 ; set Z probe trigger value, offset and trigger height
M557 X98:530 Y130:530 S80:77 ; define mesh grid

Which to me doesn't make much sense, but it works, and I got a nice height map too, so I'm very happy.

Thank you!

[chrishamm]

@queevix Not quite ideal, you may find the heightmap compensation isn't 100% accurate then. The probe offset is the offset between the nozzle (or tool tip) and the probe. You should measure that and use it in G31. To adjust the homing position for Z, it's better to modify the last G1 move before G30 in your homeall.g/homez.g files.

[Queevix]

@chrishamm
That does make sense. Thanks a lot, I'll try this tomorrow