probe edge with z probe -- preliminary solution & question

oliof

Hi ~,
as you may remember, I inquired recently about using the z probe to detect bed edges because I don't have a good way to install endstops on this machine and sensorless homing works only so-so on X but works well on Y.

Some interesting observations while working on this:

I really get an error from RRF when I try to probe the bed before X and Y are homed, hence I need to set X and Y to homed using G92. M654 H0 is not sufficient (I'll eventually figure out how to home X reliably, but util then I cheat, see below).
using the z probe this way, the X offset of the probe is ignored (this is because it's not needed on the Ormerod this feature was invented for, where the X trigger is integrated in the Z arm fixture at the right offset).
Trying to apply axis offsets using G10 L1 X-30 fixes the reported position, but I can't move beyond the edge of the bed (because the machine still knows that's where the endstop is).

So my question is: With an endstop triggering 30mm "early", is there a way to not use G92 to set the position and still get the right positions AND full axis movement?

here is my axis, endstop, and probe definition from config.g:

; Axis Limits
M208 X-90 Y-90 Z0 S1                                   ; set axis minima
M208 X90 Y90 Z200 S0                                   ; set axis maxima

; Endstops
M574 X2 S3                                             ; configure sensorless endstop for high end on X
M574 Y2 S3                                             ; configure sensorless endstop for high end on Y
M574 Z1 S2                                             ; configure Z-probe endstop f	or low end on Z

; Z-Probe
M558 P5 C"!^e0stop" H5 F300 T6000                      ; set Z probe type to switch and the dive height + speeds
G31 P500 X-30 Y-15 Z2.805                              ; set Z probe trigger value, offset and trigger height
M557 X-85:59 Y-85:70 P5                                ; define mesh grid

For testing, without touching the actual home*.g files, I wrote the folloing macro homexwithzprobe. Says what it does on the tin.

; -- lie about print head location so I can probe Z 
; -- dangerous!
G92 X0 Y0
; -- probe bed. If we can't, something is amiss.
G30

if not move.axes[2].homed
  abort

; -- wait a hot second
G4 S1 
; -- invert z probe compared to normal bed probing operations
M558 P5 C"^e0stop" H5 F300 T6000 
; -- wait a hot second
G4 S1
; -- configure X to have z probe as endstop on the low end
M574 X1 S2
; -- absolute moves
G90
; -- go to low z value
G0 Z1
; -- relative moves
G91
; -- home towards low edge of the X bed
G1 H1 X-200 F3000
G4 S1
; -- move a bit onto the bed again
G1 X10 F3000
; -- re-home slowly
G1 H1 X-200 F300
; -- wait a hot second
G4 S1
; -- z probe X offset not applied, force position
G92 X-60

; -- re-set z probe to normal mode
M558 P5 C"!^e0stop" H5 F300 T6000 
G31 P500 X-30 Y-15 Z2.805
; -- absolute mode
G90
; -- move to center of bed
G0 X0 Z10 F1200
; -- re-home Z for good measure
G30