Z height strangeness

Drammy

Hi all,

Fairly new to 3d printing and certainly new to the Duet Wifi.

Have got a problem where I (manually) level my bed as I have no IR probe and when I got to print always starts about 0.2mm below the freshly levelled z0.

I don't understand why I can home everything, level the bed on multiple positions and then when it comes to printing the print starts at a completely different z height.

How can it go lower than z0 as set by my Z end stop (two wire close/open switch)?
And why is it doing it??

EDIT:
I have no z offset in the GCode of my slicer (Simplify 3D)

My end stop set up is as follows:

[[language]]
; Endstops
M574 X1 Y1 Z1 S0                                                               ; Set active low endstops
M558 P0 H5 F120 T6000                                                          ; Set Z probe type to switch and the dive height + speeds
G31 P500 X0 Y0 Z0                                                              ; Set Z probe trigger value, offset and trigger height
M557 X25:175 Y25:175 S20                                                       ; Define mesh grid

Note: G31 was set as

G31 P500 X0 Y0 Z2.5

so I changed it to 0 with no difference.

Should I have increased it instead?

dc42

Please post the contents of your homez.g and homeall.g files.

Drammy

Here's homez.g

[[language]]
; homez.g
; called to home the Z axis
;
; generated by RepRapFirmware Configuration Tool on Mon Mar 05 2018 14:15:11 GMT+0000 (GMT)
G91               ; relative positioning
G1 Z5 F6000       ; lift Z relative to current position
G1 S1 Z-185 F1800 ; move Z down until the switch triggers
G92 Z2.5           ; set Z position to trigger height

; Uncomment the following lines to lift Z after probing
;G91              ; relative positioning
;G1 Z5 F100       ; lift Z relative to current position
;G90              ; absolute positioning

And here's homeall.g

[[language]]
; homeall.g
; called to home all axes
;
; generated by RepRapFirmware Configuration Tool on Mon Mar 05 2018 14:15:11 GMT+0000 (GMT)
G91                     ; relative positioning
G1 Z5 F6000             ; lift Z relative to current position
G1 S1 X-205 Y-205 F4800 ; move quickly to X and Y axis endstops and stop there (first pass)
G1 X5 Y5 F6000          ; go back a few mm
G1 S1 X-205 Y-205 F360  ; move slowly to X and Y axis endstops once more (second pass)
G1 S1 Z-185 F1800 S1    ; move Z down stopping at the endstop
G90                     ; absolute positioning
G92 Z2.5                ; set new Z position
;G1 Z5 F100             ; uncomment this line to lift the nozzle after homing

I'm guessing the problem is those G92 commands?
Should they be set to 0 then?

If so, I'm curious why the riprap configure tool sets this as default. Especially when it clearly seemed to understand that I had a z end stop switch only and no probe.

Surely it would have been better for it to default to 0 and not wreck peoples beds

Drammy

OK, so I've altered the home files' G92 commands to Z0 and it has worked well. Phew!

@dc42: thanks for pointing me in the right direction. (great board btw)