Zero point when using Z-Probe is too low

[nmistry]

Adding this issue from my Reddit Comment

Z-Probing seems to be inaccurate. I set the depth to 14.09 (as measured by my calipers), run the homing, and then goto Z zero. The bit always digs into the material by about 0.8mm. This irregularity is not present when homing in UGS or Candle. Probably something I have misconfigured, but figured it was worth sharing.

This test was done on a SainSmart 3018 PROVer w/ grbl 1.1f and 1/8" flat nose end mill bit.

Happy to share any additional details.

$I
[VER:1.1f.20170801:]
[OPT:V,15,128]

$G
[GC:G0 G54 G17 G21 G90 G94 M5 M9 T0 F0 S0]

$$
$0=10
$1=25
$2=0
$3=2
$4=0
$5=0
$6=0
$10=3
$11=0.010
$12=0.002
$13=0
$20=1
$21=1
$22=1
$23=3
$24=20.000
$25=500.000
$26=250
$27=1.000
$30=10000
$31=0
$32=0
$100=800.000
$101=800.000
$102=800.000
$110=2000.000
$111=2000.000
$112=600.000
$120=10.000
$121=10.000
$122=10.000
$130=500.000
$131=400.000
$132=100.000

[nmistry]

Adding a screenshot of the console after Z-probing.

This is the height where the bit touches the work surface.

Photo of the result.

[nmistry]

Some additional information. Per SainSmart's documentation, here is the probe code.

G91 G21
G38.2 Z-50 F100
G92 Z14.09
G0 Z15
G90
M30

The resulting execution in Candle

ok
G91G21G38.2Z-50F100 < [PRB:-348.343,-364.003,-7.621:1]
ok
G92 Z14.09 < ok
G0Z5M30 < [MSG:Pgm End]
ok
[GC:G1 G54 G17 G21 G90 G94 M5 M9 T0 F100 S7000]
ok

Lowering Z approaching 0.00, the bit contacted the workpeice at 0.1mm which could be a result of material thickness variation.

[kglovern]

This should be fixed in the next build. The probe module wasn't updating to use the correct plate thickness as entered in the settings - that's why the command was "G10 L20 P1 Z15" when it should be "G10 L20 P1 Z14.09".

Thanks for the report!