BLTouch - Probe trigger height ineffective?

drmaestro · 8 Mar 2018, 16:01

Hi,

I have a problem with the first layer of the prints. I have set the Z trigger value, which should be the main factor determining how high the nozzle will be when it starts printing (of course the first layer height is the main determinent, however it depends on trigger height). My nozzle starts too high when printing and changing the Z trigger value doesn't seem to affect it. Also, babystepping seems to be ineffective (it doesn't lower the nozzle). Am I doing something wrong? Is there another detemining factor for the nozzle's height?

Thanks

dc42 · 8 Mar 2018, 16:17

Do you have a G31 command in config-override.g that is overriding the one in config.g that you are changing?

drmaestro · 8 Mar 2018, 16:43

I don't have a config-override.g file.

dc42 · 8 Mar 2018, 17:51

How have you set the Z trigger value, and how are you homing the Z axis of your printer?

drmaestro · 3 Aug 2018, 18:13

That's my G31 command on config.g:

G31 X30 Y0 Z2.2 P25 ; Set Z probe trigger value, offset and trigger height

And the following lines are from homez.g:

; Lift Z relatively to current position
G91
G1 Z5 F4800
G90
G1 X100 Y100 F3000 ; Go to safe loaction
G91
G30
G90

Probably some of the G90s or 91s are unnecessary?

The Z homing portion of homeall.g is as follows:

; Move Z down until the switch triggers
G1 X100 Y100 F3000

G90
G30

; Absolute positioning
G90

; Uncomment the following line to lift the nozzle after probing
G1 Z5 F80

dc42 · 8 Mar 2018, 18:46

Looks OK to me. Is your G31 command later than the M558 command in config.g (it needs to be)? Are you sure that you don't have a second G31 command somewhere?

You can check the current setting of the G31 trigger height by sending G31 Tn where n is the P parameter in the M558 command

gavatron3000 · 12 Mar 2018, 14:37

Out of curiosity have you setup your bltouch EXACTLY as it states in the documents from antclabs? The distance from the nozzle tip to the end of the plastic housing is important. 8.3mm from memory on mine which gives me a trigger height of 0.87mm

Ret · 15 Mar 2018, 02:14

I had to add a negative value to my minimum z height since the firmware would block any negative z offset.

M208 X0 Y0 Z-2 S1 ; Set axis minima

G31 P25 X35.25 Y0 Z1.25 ; Set Z probe trigger value, offset and trigger height. The higher the "Z" value, the closer the bed will get to the nozzle.