Transcript Understanding Gauge R & R

My Personal Crusade
UNDERSTANDING GAUGE R&R
Mark S. Rusco
Innovative Corporate Training
[email protected]
WHAT DO EV, AV, RR REPRESENT?
Each is just a Standard Deviation.
 From Page 115 of the MSA (2nd Paragraph)


And from Page vi
YOU CAN ADD VARIANCES, BUT NOT S.D.

Page 55 reminds us to add variances, not
standard deviations.
A SIMPLE EXAMPLE
X
0
20
40
60
80
100
A SIMPLE EXAMPLE
XX
0
20
40
60
80
100
A SIMPLE EXAMPLE
XXX
0
20
40
60
80
100
A SIMPLE EXAMPLE
X
XXX
0
20
40
60
80
100
A SIMPLE EXAMPLE
X
X XX
XX XXX X
0
20
40
60
80
100
A SIMPLE EXAMPLE
X
X XX
XX XXX X
0
20
40
60
80
100
A SIMPLE EXAMPLE
X
X XX
XX XXX X
0
20
40
60
80
78
100
A SIMPLE EXAMPLE
This Standard
Deviation defines the
Error of Width
X
X XX
XX XXX X
0
20
40
60
80
78
100
This distance
defines Error of
Location
ERRORS OF LOCATION
Bias
 Linearity
 Stability
 Averaging several readings does not help.
 Found by measuring known standards.
 Eliminate/minimize by calibration.

ERRORS OF WIDTH
Repeatability
 Reproducibility
 Averaging several readings reduces error.
 Found by repeated measurements of the same
parts.
 Minimize by operator training, gauge
improvement, etc.

SUMMARY SO FAR
R & R are both Standard Deviations
 We combine them as Variances to get GRR
 There’s a major difference between Errors of
Location and Errors of Width.

YOU’RE NOT SAMPLING CORRECTLY

Pg 74, in bold letter, tells us how to sample
YOU’RE NOT SAMPLING CORRECTLY

“selected from the process” is not:
 Consecutive
parts
 Random Parts

At least one part should be as small as
normally expected, and one part should be as
large as normally expected. All the other “inbetween” parts don’t really matter.
YOU’RE NOT SAMPLING CORRECTLY

Start with Equation for %GRRtv
YOU’RE NOT SAMPLING CORRECTLY
Substitute in EV and AV for RR.
 Substitute in RR and PV for TV

YOU’RE NOT SAMPLING CORRECTLY

Substitute in EV and AV for RR on the bottom

%GRRtv is driven by PV.
YOU’RE NOT SAMPLING CORRECTLY

What drives PV?
PV
= Rp x K3
Rp = Biggest Part – Smallest Part
 You
want Rp to be as big as possible,
so %GRRtv is as small as possible.
SUMMARY OF SAMPLING
Sort through your parts to find the biggest and
smallest part you can find.
 This makes Rp big, which makes PV big, which
makes %GRRtv small.
 Small %GRRtv makes your life easier.

INTERPRETING THE RESULTS
You know the Standard Deviation of your Gauge
System. Is it a good gauge?
 Can the gauge discriminate between Good/Bad
Parts?
 Can the gauge detect process variation?

INTERPRETING THE RESULTS

Can the gauge discriminate between Good/Bad
Parts?

Answered by %GRRtot tol
%GRRtot.tol.
 6 * GRR 
 100* 

 Tot.Tol. 
INTERPRETING THE RESULTS

Can the gauge detect process variation?

Answered by %GRRtv
INTERPRETING THE RESULTS

Just because %GRRtv <10% and %GRRtot tol
<10% doesn’t mean the situation is good.
Which situation is better for your company?

%GRRtv = 6% and %GRRtt = 9%
 OR

%GRRtv = 15% and %GRRtt = 9%


INTERPRETING THE RESULTS
INTERPRETING THE RESULTS
SUMMARY OF INTERPRETING RESULTS
Understand the difference between %GRRtot tol
and %GRRtv
 Don’t plug your data into software and blindly
accept the %GRR values.
