Calibrate Z probe trigger height

[hmortensen]

Hi

I've got an Ender 3 pro with Duet2Wifi and BlTouch v3.1 sensor.
Everything else is stock.

FW: 2.03 (2019-06-13b2)

I've followed this guide:
https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe#Section_Calibrate_the_Z_probe_trigger_height

But when I issue "G30 S-1" repeatedly, the height increases with every probing.

Config for probe:

M574 Z1 S2
M307 H3 A-1 C-1 D-1
M558 P9 H5 F500 T4000
G31 P500 X-43 Y-6 Z2.845
M557 X10:200 Y10:200 S20

Result of 10 probings (last is first):

Stopped at height 2.932 mm
Stopped at height 2.922 mm
Stopped at height 2.920 mm
Stopped at height 2.912 mm
Stopped at height 2.908 mm
Stopped at height 2.908 mm
Stopped at height 2.900 mm
Stopped at height 2.895 mm
Stopped at height 2.890 mm
Stopped at height 2.882 mm

Any ideas to solve this?

[Veti]

this would suggest a mechanical issue.
is the mount for the bltouch stable and has no play?

[EasyTarget]

As @Veti says.. it looks remarkably like something is not properly tightened and moving slightly with each probe. I've been there, it's confusing. But as far as I know there is no way of mis-configuring the Duet which could cause this, so look to hardware.
Another option is the Z axis maybe hitting it's limit at the very last moment and dropping a step or two just as the probe is triggering.. that would push your height off too.

[Phaedrux]

@hmortensen said in Calibrate Z probe trigger height:

M558 F500

Reduce your feed rate by 1/5th to F100

G31 P500

Reduce your trigger threshold to P25

You're probing too fast and with too little sensitivity

[hmortensen]

Hi

Thanks for your inputs.

I've concluded that my Z axis is offbeat.

[Phaedrux]

@hmortensen can you elaborate?