RC Metrology Consulting

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

  = 2²   = 3²   = 4²   = 5²   = 6²   = 7²   = 8²   = 9²   = 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 3 rd 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 = ”  1 Sigma = ”  68% ” – ”  95% – ”  99.97% – ”

The Histogram

Use the Histogram

Play the Odds

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

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”

95%.0003”.0015”

References and Acknowledgements  MSA 3rd Edition by AIAG  Mitutoyo of America  Cliff’s Quick Review - Algebra, Statistics, and Geometry  ASME Y 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