5) CMM Measurement Applications

Question 1

What is the general measurement strategy for CMM’s? (8 steps)

Answer 1

1. Select features to be measured
2. Define datums used within coordinate system
3. Select workpiece orientation
4. Workpiece holding method
5. Qualification of CMM probe (location)
6. Define probing strategy
7. Programme CMM
8. Analysis and results

Question 2

Should all features be measured using a CMM?

Answer 2

No, some features cannot be measured using a CMM. (cost, ease)

Question 3

What should be done to the coordinate system before measuring commences?

Answer 3

Calibrate the CMM coordinate system with the coordinate system of the part.

Question 4

Describe the coordinate systems for a cylinder and sphere.

Answer 4

Cylinder - one rotary, 2 linear

Sphere - two rotary, 1 linear

Question 5

Describe probe tip qualification.

Answer 5

5 points taken around a sphere to calibrate location of cmm probe.

Question 6

What is BS 7172 (1989) ?

Answer 6

The governing standard for the approved maths used in the coding for the CMM software.

Question 7

What are the minimum and recommended number of contact points for measuring a line, plane, circle and sphere?

Answer 7

Straight line - min 2, rec 5
Plane - min 3, rec 9
Circle - min 3, rec 7
Sphere - min 4, rec 9

Question 8

What should be considered when measuring circular shapes?

Answer 8

If lobing has occurred.

Question 9

What are the 2 types of error found in CMM data points?

Answer 9

Form deviation.

Measurement errors.