probe xy offset

jens55

I am in the process of commissioning a new printer build and am having slight difficulties with the x/y offset.
I have done the offset measurements and entered them via G31 in config.g. I wish to confirm that the offset works. If my nozzle is currently at x150 y150, what command do I use to probe at x150 y150?
What I expect to happen if I do a g30 x150 y150 is that the carriage moves by the offset amount entered during the startup via g31. In real life the carriage does not move but does the probing right where the nozzle is (ie x150 y150) but the probe is like 30 mm offset.
What part of the xy offset am i not understanding correctly.

Just to add, in config.g I also have "g10 x0 y0 z0" before the G31 offset command.

M563 S"Nozzle 0" P0 D0 H1 F1 ; define tool 0
G10 P0 X0 Y0 Z0 ; set tool 0 axis offsets
G10 P0 R0 S0 ; set initial tool 0 active and standby temperatures to 0C

My understanding is that in a single nozzle printer G10 should be all zeros .....

jay_s_uk

@jens55 G30 will only probe and an X/Y co-ordinate position when a Px value is involved.
So if you sent g30 x150 y150, the X/Y co-ordinates would be ignored and it would probe at the current position.
You are correct about G10.

So to summarise, you have to manually (in your head) consider X/Y probe offsets when using G30 without a P value to make sure the nozzle is in the correct position however you don't need to consider probe offsets if you are using a P value with G30

jens55

@jay_s_uk, thank you! I figured I am just missing or misinterpreting a minor little thing but I would have never figured that out by myself. I will experiment with this tomorrow.
What other commands use the offset value bedsides g30 and presumably g29? When I am doing homez.g, I go to the middle of the bed and then do a g30 .... but the BLTouch is at a completely different spot so why am I doing a plain g30 to set my z=0 point? What is the point of trying to get z=0 as accurate as possible while the probe that does the measuring is 30mm offset from the nozzle position.

jay_s_uk

@jens55 for homez, you need to move to a location that takes into account the probe offsets. so if you want to probe the centre of the bed, you would move to the centre, minus the offset. e.g.

G1 X{(move.axes[0].min + move.axes[0].max)/2 - sensors.probes[0].offsets[0]} Y{(move.axes[1].min + move.axes[1].max)/2 - sensors.probes[0].offsets[1]} F3600

For G29, you need to take into account the offset when setting the mesh limits. e.g. if your probe is on the right of your nozzle by 20mm, to start probing a mesh anywhere to the left of X20, the nozzle would have to be at X0 or less. Its not the end of the world if you do get this wrong because as long as your axis limits are correct as RRF will just tell you that your probe points are unreachable and skip them.