Z Probe Inconsistent Results

How To
1

I am running into inconsistencies using the Z probe feature of the UGS. About 50% of the time it works as expected–bit hits the surface and is retracted (quite a bit) with the proper math done to Z. About half the time it retracts a very small amount and then plunges into the bed as if everything was mirrored on Z. First theory was that maybe I started with a Z too low before initiating the probe. This does not appear to be the problem.

Can’t figure out a pattern as to why this is happening(?)

Using UGS Product Version: Universal Gcode Platform 201609300101

GRBL 0.9j.20160317

2

Can you keep an eye on the Log? Copy out that? It should show in plain text what commands are sent and how the machine is reacting.

3

I haven’t had one fail in the last few days (not using the machine mostly). Here is what a successful one looks like just to keep the thread alive:

[PRB:-787.400,-266.000,-37.850:1]

ok
ok

G10 L20 P1 Z3.1
ok
G90 G21
G90 G21 G0 Z15.0
G90 G21

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4

And this probe crashed back into the metal block after a small retraction

ok
[PRB:-787.400,-266.000,-37.850:1]
ok
ok

G10 L20 P1 Z3.1
ok
G90 G21
G90 G21 G0 Z15.0
G90 G21

5

Nobody? The console log is exactly the same but the behavior is completely different. No theories out there?

6

I believe that that would qualify as a bug report w/ the folks making the comm / control software you’re using and with @chamnit w/ Grbl on github.

7

Sounds like mechanical to me. It’s fairly common for a z axis to lose steps when moving up due to gravity. Check you linear rails and leadscrew for abnormal wear and try cleaning and lubing them per manufacturer guidelines.

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8

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