Strange move of 0 Point for Z axis when using mesh

HolgerB

Hi,

I have a strange effect with bed compensation

I am using the IR probe (V2). To get the correct trigger height I used the method describred https://www.duet3d.com/wiki/Using_mesh_bed_compensation with a manually calibrated bed and got 2.07mm for the trigger height.

So I setup config.g:

[[language]]
; ## ALLGEMEINES
M550 PYellow Monster	; Name des Printers
M552 S1                 ; Verbindung mit WiFi aufbauen

; ## BEWEGUNG
; M569 P0
M569 P1 S0			; X: Drive 1 vorwärts
M569 P2 S1			; Y: Drive 2 rückwärts
;M569 P3
;M569 P4
M569 P5 S1			; Z: Drive 5 rückwärts
M569 P6 S1			; Z: Drive 6 rückwärts
M584 X1 Y2 Z5:6 E0:3:4		; Stepper zuordnen
M350 X16 Y16 Z16:16 E16:16:16 I1 	; 16x Mikrostepping
M574 
M906 X1200			; X-Achse: 1200mA
M906 Y2000			; Y-Achse: 2000mA in Reihe
M906 Z1500:1500			; Z-Achse: 1500mA je Motor
M906 E1800:1800:1800		; Extruder: 1700mA je Motor
M203 X12000 Y12000		; Geschwindigkeit der Achsen in mm/min
M566 X600 Y600 Z30 E20		; Maximae Gewschwindigkeitsänderung
M208 X300 Y300 Z300		; Maximale Achsenlage
M208 X-11 Y-9 S1		; Definition 0 Position
M92 X100 Y100 Z800 E100.5:100.5:100.5		; Kalibrierung der Achsen
M572 D0 S0.13			; Bowden Kompensation
M572 D1 S0.13			; Bowden Kompensation
M572 D2 S0.13			; Bowden Kompensation
G21				; Angaben in Millimeter
G90                             ; Verwendung absoluter Koordinaten
M83 				; Für Extruder relative Koordinaten

; ## Z-PROBE / HOME
M671 X-8.9:38.9 Y150:150	; Achsenposition für Ausgleich 
M558 P1				; Z Probe Type
G31 P500 Y-39 Z2.07		; Triggerpunkt definieren

; ## TEMPERATUR
M305 P0 R4700 T100000 B3950	; Bett Temperatur Messung
M305 P1 R4700 T100000 B3950	; Hotend Temperatur Messung

; ## TOOLS
M563 P0 D0 H1			; Tool 0: Extruder 1
G10 P0 R0 S0 X0 Y0		; Tool 0: Offset und Temperaturen 0
M563 P1 D1 H1			; Tool 1: Extruder 2
G10 P1 R0 S0 X0 Y0		; Tool 1: Offset und Temperaturen 0
M563 P2 D2 H1			; Tool 2: Extruder 3
G10 P2 R0 S0 X0 Y0		; Tool 2: Offset und Temperaturen 0
M563 P3 D0:1:2 H1		; Tool 3: MIXER
G10 P2 R0 S0 X0 Y0		; Tool 3: Offset und Temperaturen 0
M567 P3 E0.34:0.33:0.33		; Tool 3: Standardmixer

; ## LOAD OVERRIDES
M501

and bed.g

[[language]]
; ## MESH BED LEVELLING
M208 Y340			; Temporäre Erhöhung maximale Achsenlage
M557 X20:280 Y20:280 S260	; 4 Punkt Messung zum Auto Bed Levelling
G29 S0				; Auto Bed Leveling durchführen und aktivieren
M208 Y300			; Temporäre Erhöhung maximale Achsenlage

After running G32 the trigger height changes automatically to 3.57 mm even (glass) bed is levelled quite good. What is me surprising to: When the Level map is displayed all 4 Z-points are around -0.7 instead of 0. So - you have an idea where I made the error?

Best regards
Holger

dc42

Do you have a config-override.g file containing a G31 command that is overriding the trigger height you set in config.g?

HolgerB

No - content of config-override.g is below - but shouldn't in that case not also the trigger position after homing different? That changes after G32

Best regards
Holger

HolgerB

In the meantime I fear that is related to the fact, that the sensor do not give reproducable results for my glass bed :(.

What I have done to come to this conclusion: With help of a piece of paper I measured manually 9 points in a 200 x 200 mm square. Afterwards I defined the same square and the 3x3 matrix with M557. The result was frightening: Even for the point where homing was made before a height of 0.3 mm is measured and the other results do not really fit to my manual measured results.

So - do you think I would get better results wit the new BL touch? I read something about an ultrasonic sensor but didn't see any sensor like this. Any other suggestions?

Best regards
Holger

dc42

Is your glass bed backed by a black surface as the fitting instructions require?

HolgerB

No because there is written:

works as-is if placed directly on a PCB bed heater or other surface that does not reflect strongly.

and it ist directly placed on a PCB bed heater…

Dougal1957

and is that PCB Heater perfectly plain or does it have any printing on it?

HolgerB

No - there is a printing on it, but I checked already whether there is a difference or not - it does not matter. The lack of accuracy is all over the area

dc42

What colour is the PCB heater?

Dougal1957

Bet it's red with white printing on it and shiny to boot?

HolgerB

It is red to brown with black printing

dc42

Try putting black paper between the bed heater and the glass.

SputnikOC3d

Not sure if my issues are same - but def similar … Ive LOST Z0 and cannot seem to get back to it with a BL Touch ...