National Research Council
Canada		 Conseil national de recherches
Canada

Institute for National
Measurement Standards

Institut des étalons
nationaux de mesure
Ottawa, Canada
K1A 0R6

 

22 October 2001

Subject: CMM Workshops – Uncertainty Estimation & Practical CMM Measurement

The NRC is planning to organize several CMM related workshops. If the interest level is high enough, these workshops would be scheduled for February/March of 2002 at the NRC Institute for National Measurement Standards in Ottawa, Ontario, Canada. If you know of any companies or persons that might be interested in the opportunity to attend such informative workshops, please contact Kostadin Doychinov by phone at (613) 991-0265, or via email at kostadin.doytchinov@nrc.ca.

Subjects for possible NRC workshops

1 One day CMM workshop geared towards uncertainty estimation recommended for CMM calibration engineers and technicians, people involved with uncertainty estimation of CMM measurements. The workshop will include such topics as:
1.1 Dimensional Metrology Basics 
1.2 Measurement Uncertainties – terms and definitions
1.3 Measurement Uncertainties – basic concepts, expression of uncertainties, combining uncertainties 
1.4  The CMM – understanding the mechanical structure
1.5  The 21 geometrical error sources
1.6 Equipment used to collect data about the 21 error sources
1.6.1 Laser interferometers – principle of operation, practical example, uncertainties
1.6.2 Electronic levels– angle (differential rotation measurements)
1.6.3  Z axis roll measurements
1.6.4 Squareness measurements
1.7 The propagation of the geometrical errors, example of a simple mathematical model for error compensation (error mapping)
1.8 The influence of the ambient conditions
1.8.1 Temperature, Humidity, Barometric pressure
1.9

 Probing
1.9.1

 Probe Calibration – why needed, goals and results
1.9.1.1 Single stylus
1.9.1.2 Multiple stylii, multiple probe positions
1.9.1.3  Practical advice
1.10

CMM verification standards (B89.12M, ISO 10360-series)
1.10.1

The ISO 10360 series of CMM verification standards - discussions
1.11  Material standards used for CMM verification (gauge blocks, ball-bars, ball- plates, etc).
1.12 Uncertainty of the CMM verification process
1.13 Introduction to the task dependent uncertainties of a CMM measurement – the task dependant uncertainties will be dealt with in detail at the second workshop geared towards the CMM users and programmers.
2 The second proposed CMM workshop would have a duration of one or two days (depending on your feedback). It would be geared towards practical CMM measurements – understanding designer’s intent and determining the goal of the measurement, developing a measurement strategy on a participant’s work piece (bring your part), understanding the limitations of GD&T assessment using a CMM, task specific uncertainty estimation. This workshop would be recommended for CMM operators, CMM programmers, quality engineers and technicians and would include topics like:
2.1  Measurement Uncertainties – terms and definitions
2.2 Measurement Uncertainties – basic concepts, expression of uncertainties,  combining uncertainties 
2.3 The CMM – understanding the mechanical structure
2.4 The 21 geometrical error sources
2.5 The influence of the ambient conditions
2.5.1

Temperature
2.6

Probing
2.6.1

Probe Calibration – why needed, goals and results
2.6.1.1 Single stylus
2.6.1.2 Multiple styli, multiple probe positions
2.6.1.3 Practical advice
2.7

Introduction to the ISO 10360 series of CMM verification standards
2.7.1

User’s prospective
2.8 Performing measurements with the CMM
2.9 Things to do before starting the measurements
2.9.1

Understanding the goal
2.9.1.1 Putting the drawing (CAD model) under scrutiny
2.9.1.2 What do we really want? Troubleshooting or Tolerance compliance?
2.10 Designing the measurement strategy
2.11 Choosing accessories and clamping
2.12 Datum Reference Frame (DRF) and Coordinate System
2.12.1 Do they always mean the same?
2.12.2 Principles of building a DRF 
2.12.3 Examples of ambiguous, over constraint or not fully constraint DRF (or  Coordinate System).
2.12.4 Understanding how to deal with it – practical advice. 
2.13

Geometrical Features
2.13.1

How are they calculated?
2.13.1.1 Least Squares, Min-Max, etc.
2.13.2 

Sampling strategies
2.13.3 What is the difference between the constrained and non-constrained  geometrical elements? 
2.13.4 Form measurements with a scanning probe
2.13.4.1 Introduction to data filtering for form measurements
2.14

Geometrical Tolerances
2.14.1 Y14.5 and ISO 1101 standards
2.14.2 Different tolerance zones and practical advice on best way to approach it.
2.14.3 The “material condition or vectoring” approach.
2.14.4  The concept of MMC, RSF and LMC
2.15

Task Related Measurement Uncertainties (accuracy) 
2.15.1 Practical session on estimating measurement uncertainties on a client’s part using readily available standards like gauge blocks, ring gauges, ballplate, etc.
2.15.2  Possible methods for estimating task related uncertainties – using the CMM in a comparator mode
2.15.3 Making higher accuracy measurements with the CMM. Reversal  techniques
2.16

Measurements of known surfaces
2.16.1

Using the “material condition” approach
2.17

Measurements of unknown surfaces
2.17.1 Tip radius correction on a free surface - cosine error
2.17.2 Data clouds to CAD model Best-fitting
2.18

CMM programming
2.18.1  Why a good software programmer is not necessarily a good CMM programmer? 
2.18.2 Useful tips for CMM programmers

 

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