Metrology 5

Question 1

How can out of roundness be specified?

Answer 1

If a centre is found the distance between point on the periphery

Question 2

Simplest method for measuring roundness?

Answer 2

Using a V-block and dial gauge with the component rotated slowly.

Question 3

How can false readings be generated and what is a better method?

Answer 3

Regularly spaced features. rotating between centres is more accurate

Question 4

What are other types of roundness measuring

Answer 4

One type of machine has a stationary measuring head and a rotating work piece (1), whilst the second type has a rotating measuring head and a stationary work piece (2).

Question 5

Advantages of stationary head systems

Answer 5

measurement pick up is more easily adapted to measurements of concentricity and alignment
measurement head is more free to move
Straightness measurement can be made

Question 6

Disadvantages of stationary head systems

Answer 6

the precision spindle of the rotating turn table limits the mass and size of the workpiece
Computer aided centring and automatic centring is not available

Question 7

Why are measurements magnified?

Answer 7

Variations can be vary small (microns)

Question 8

What is the minimum zone reference circle

Answer 8

two concentric circles that just enclose the profile and have minimal radial separation. The maximum radial distance between the two circles is the out of roundness value.

Question 9

What is the maximum inscribed reference circle?

Answer 9

(plug Gauge centre) the largest circle which is just contained in the trace. The out of roundness value is the height of the largest peak above the circle

Question 10

What is the minimum circumscribed reference circle?

Answer 10

(ring gauge centre) the smallest circle that will just contain the trace. Out of roundness is defined as the depth of the lowest valley below the circle

Question 11

What is the least squares reference circle?

Answer 11

can be regarded as representing the average of all the peaks and valleys (minimum departure calculation). The out-of-roundness is a function of the radial distance of the maximum peak (P) from the circle and/or the distance of the maximum valley (V)
from the circle.

Question 12

What is eccentricity

Answer 12

Eccentricity is the term used to describe the position of the centre of the profile relative to some datum point. Denoted as a distance (mm) and an angle (degrees).

Question 13

What is concentricity

Answer 13

fined as the diameter of the circle described by the profile centre when rotated about the datum point.