Skipping gridpoint during probing despite offset inclusion

singhm29

Howdy all,

Switched out my hotend/extruder and had another go at fixing issues I've always had with my mesh probing.

Essentially my mesh does not probe an entire column saying that it cannot reach the location despite actually being able to.

M208 Axis limits X0.0:609.0, Y-3.0:611.0, Z0.0:578.5
M557 Grid: X-31.0:594.0, Y3.0:562.0, radius -1.0, X spacing 156.2, Y spacing 139.8, 25 points
G31 Z probe 0: current reading 1000, threshold 25, trigger height 2.850, offsets X31.0 Y-44.0

After reading previous posts I tried including my probe offsets to no avail it still misses an entire row closest to X0, basically any point with an X coordinate of 0 will be skipped. I have tried increasing my axis limit to be -31 without a change, I have tried with it as 0 for the M557 grid.

To add to this oddity if I run G32 it for some reason overshoots my X0 point and tries going past my endstop for a bit before stopping and probing, the second pass it has no issue stopping at X0 and running correctly.

Any thoughts would be much appreciated.

; bed.g
; called to perform automatic bed compensation via G32
;
; generated by RepRapFirmware Configuration Tool v3.2.3 on Mon Mar 15 2021 19:09:36 GMT+0100 (Mitteleuropäische Normalzeit)
M561                                                       ; Clear any existing bed transform.
G28 ; home
G1 X300 Y300 F4000 ; go to center of bed this isnt in his
;G1 Z220 F10000 took this out since we dont wanna raise
;M558 F10000
G30

; first pass
G30 P0 X0 Y300 Z-99999 ; probe near a leadscrew, half way along Y axis
G30 P1 X560 Y300 Z-99999 S2 ; probe near a leadscrew and calibrate 2 motors
; second pass
G30 P0 X0 Y300 Z-99999 ; probe near a leadscrew, half way along Y axis
G30 P1 X560 Y300 Z-99999 S2 ; probe near a leadscrew and calibrate 2 motors

;G1 X10 Y210 Z10 F10000

jay_s_uk

@singhm29 it won't get to X0
your config tells the machine that your probe is 31mm to the right.
To get the probe to X0, your nozzle has to be at X-31. This is outside the limits set in M208.
G29 respects the limits of that.
Also when setting up a mesh, you have to take into account that offset when you set the mesh up.

I have a feeling that G32 does not respect the M208 limits.
Move your probe point closer in to X35. Getting it as close as you can to the screws is helpful but not critical

fcwilt

@singhm29

Your G31 has X31 Y-44.

Your M557 has X-31 (and you say you tried X0).

To move the probe to X-31 would require moving the nozzle to X-62 - can it do that?

To move the probe to X0 would require moving the nozzle to X-31 - can it do that?

One sure way to obtain workable values for M557 or the G30 P# commands is to compute X and Y min/max values for the probe.

The 31 and 44 below are the absolute values of the probe X and Y offsets:

Xmin probe = Xmin + 31
Xmax probe = Xmax - 31
Ymin probe = Ymin + 44
Ymax probe = Ymax - 44

Then use these new X and Y values in M557 and the new X values in the G30 P# commands.

Now this wont cover as much area as possible but it will insure the area covered is reachable by the probe.

Frederick

singhm29

@jay_s_uk Thanks for the thoughts I will test this out but what I fear here is that if I change M208 to M208 X-31:609 Y-3:611 Z0:578.5 is that this may fix the probing but when I home X it will think that when it hits home its -31 which would be wrong. Interesting regarding the lead screw and I will try that out as well.

fcwilt

@singhm29

Well if you don't wish to use values that insure the probe is with an area that can be reached you can set the M208 value to the desired values and use M564 S0 to temporarily allow movement outside the limits of M208.

But you still need to insure the nozzle can actual move to the locations required for the probe to reach the locations specified in M557 or the G30 P# commands.

Frederick

Phaedrux

@singhm29 said in Skipping gridpoint during probing despite offset inclusion:

@jay_s_uk Thanks for the thoughts I will test this out but what I fear here is that if I change M208 to M208 X-31:609 Y-3:611 Z0:578.5 is that this may fix the probing but when I home X it will think that when it hits home its -31 which would be wrong. Interesting regarding the lead screw and I will try that out as well.

Only set M208 to X-31 if X0 is still on the bed and the print head can actually travel to X-31.

The simple fact of the matter is that the probe may not be able to reach all points that the nozzle can.

singhm29

@fcwilt Hey thank you very much for your feedback as well I went ahead and tried what you advised above and it worked very well! Makes alot of sense to use that approach to keep things simple and I am now happy to report all points are probed and it gets quite close to the edge on each side still.

I used @jay_s_uk tip on changing my probe point to X35 and that also fixed my ramming of my X endstop when executing G32.

Thank you for the help, looks like probing is figured out for now!