RC Metrology
Consulting
[email protected]
What does
it measure?
Know the uncertainty of your
CMM using a $10 calculator…
Outside the Box
 “So we fix our eyes not on
what is seen, but on what is
unseen. For what is seen is
temporary, but what is
unseen is eternal…”
Outside the Box
Outside the Box
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1 + 3 = 2²
1 + 3 + 5 = 3²
1 + 3 + 5 + 7 = 4²
1 + 3 + 5 + 7 + 9 = 5²
1 + 3 + 5 + 7 + 9 + 11 = 6²
1 + 3 + 5 + 7 + 9 + 11 + 13 = 7²
1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 = 8²
1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 = 9²
1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 = 10²
CMM game plan
 Order it up…
 We will establish a strategic,
easy to implement, statistical
system to learn the certainty
of any given CMM application
 Plan, Do, Check, Action…
Our Goal
 To improve the measurement
capability of our CMM by
increasing the certainty of the
measurements we are
making.
 This improvement may seem
to be very small.
Small Improvements
 The difference between a
career in the Minor Leagues
and the Baseball Hall of Fame
is only 1 more hit per week.
 A Baseball season is played
April – September = 26 weeks
The Minor Leagues
 In a normal season a player
will encounter 500 at-bats.
 125 hits in 500 at-bats…
 125 / 500 = .250 batting
average.
 Toledo Mudhens
Imagine if ???
 If a player could get just 1
more hit per week…
 151 hits in 500 at-bats…
 151 / 500 = .302 batting
average.
 The Hall of Fame
Uncertainty???
 ISO-9000, QS-9000:1994, state:
“Inspection measurement and test
equipment shall be used in a
manner which ensures that the
measurement uncertainty is known
and consistent with the required
measurement capability.”
Uncertainty???
 TS-16949: Recommends internal
inspection labs comply with ISO/IEC
17025… “When estimating the
uncertainty of a measurement, all
uncertainty components which are
of importance in the given situation
shall be taken into account using
appropriate statistical methods of
analysis.”
Uncertainty???
Doesn’t it?
Can’t we?
Right???
Isn’t it?
Don’t they?
Uncertainty is:
 The upper estimated limit of
how wrong a given reading
(or value) can be.
 Kerry 53% Bush 47% (±4%)
 Kerry 57% Bush 43%
 Bush 51% Kerry 49%
The True Value is:
 Always unknown and
unknowable (MSA 3rd edition)
 Average value taken from an
infinite number of readings.
The Plug Gage Paradox
 Tell me what it measures:
Outside Diameter.
 Caliper (.001”)
 Micrometer (.0001”)
 Bench micrometer (.00005”)
 How many readings (1,3,9,12)
The Plug Gage Paradox
 Where do we measure? (on
the end or in the center)
 What if it’s not round (and it
won’t be)
 Diameter ????????
The Plug Gage Paradox
 Because the measurement
definition was not clearly
defined we will never be
certain of our measured
result.
Measurement Definition
 Micrometer .0001”
 3 readings each end and
middle (Total n=9)
 Report 9 reading average,
minimum reading, and
maximum reading
Standard Deviation
 Sigma
 Spread of measurement data
Standard Deviation
Sample Data Collection
 Must be RANDOM
 Attempt to represent the
entire population
 The sample will always be a
sample and display less
variation than the population
Sample and Population
 Clock cars in a designated
45mph speed limit zone
 6 hours / 1 week = Ave, min,
and max
 24 hrs / 4 weeks = Ave, min,
and max
 120 hrs / 26 weeks = Wow!
Probe calibration controversy
 Define the measurement
 Probe 9 points on 1” master
sphere: 8 points around
equator and 1 point on north
pole
 3 measurements / 25 days
1” Sphere results
 75 reading ave = .999878”
 1 Sigma = .000088”
 68% .999790” – .999966”
 95% .999702 – 1.000054”
 99.97% .999614 – 1.000142”
The Histogram
20
18
16
14
12
10
8
6
4
2
0
0.99950
0.99960
0.99970
0.99980
0.99990
M e a s ure m e nt
1.00000
1.00010
1.00020
Use the Histogram
20
18
16
14
12
10
8
6
4
2
0
0.99950
0.99960
0.99970
0.99980
0.99990
M e a s ure m e nt
1.00000
1.00010
1.00020
Play the Odds
20
18
16
14
12
10
8
6
4
2
0
0.99950
0.99960
0.99970
0.99980
0.99990
M e a s ure m e nt
1.00000
1.00010
1.00020
CMM game plan
 Before we start measuring
our parts we can measure
the 1” master sphere 3 times
and compare our results to
our Histogram.
 Do we want to order it up?
Concentricity of a Perfect Part
Define the Measurement
 5 point XY Baseplane
 12 point Cylinder as Z axis
 9 point Circle (bottom) as XY
origin and Datum
 9 point Circle (top) as feature
 3 measurements / 25 days
The Histogram
Ring gage concentricity
 75 reading ave = .00015”
 1 Sigma = .00009”
 47.5% of the time (or + 2
sigma) it measured worse
than .00015” (or as high as
.00024”)
Another Look !
Uncertainty???
Can’t we just??? and
then just say…
Dropped parts
Can’t we just ignore
gravity????
The Myth of “True” Position
The Myth of “True” Position
The Myth of “True” Position
Define the Measurement
Define the Measurement
 7 point XY Baseplane
 5 point X axis line
 5 Point Y axis line
 XY origin at intersection
 9 point circle (Z -.100”)
 3 measurements / 25 days
Where is the center???
 Average .00092”
 1 sigma of .00030”
 68% of the time our value
obtained was between .0006”
and .0012” (.0006”)
 95% of the time our value
obtained was between .0003”
and .0015“ (.0012”)
.00092”
.0015”
95%
95%
.0003”
References and Acknowledgements
 MSA 3rd Edition by AIAG
 Mitutoyo of America
 Cliff’s Quick Review - Algebra, Statistics,
and Geometry
 ASME Y14.5-1994 Geometric Dimensioning
and Tolerancing
 H.E.S. Honda Engineering Specifications
 DCC CMM Programming - Part Alignment
and Vector Points by Scott Beavers
References and Acknowledgements
 Technical Shop Math by John G. Anderson
 Tooling and Production Magazine
 Modern Machine Shop Magazine
 Cybermetrics: GAGEtrak software
 NWCI Calibration and Inspection
 Nelson Precision - A Mitutoyo Company
 Qualtech Tool and Engineering
 Hower Tool - Ossian, Indiana
References and Acknowledgements
 NWE/Foxconn - Santa Clara, CA
 Mitutoyo of America
 SFC (Retired) Thomas J. Ravenell,
Ft. Bragg, NC
 Dave Schwab - Nelson Precision
 Terry Davis - Mitutoyo
 Mike Dukehart - Mitutoyo
 Jerry Guffy - Mitutoyo
 James Vannoy - CMM Technology, Inc.
References and Acknowledgements
 Scott Beavers - CMM Resources
 Travis East - Geometry 2.8 Freeware
 Dr. Bill McNeese
 Dr. Henrik S. Nielsen
 Gordan Skattum
 My Wife, Ramona