CNC Precision Measurement & Quality Control 2

Question 1

A CNC machinist measures a bore with an inside micrometer and gets 1.2503". The print calls for 1.2500" ±0.0003". What is the correct disposition?

Accepted Answer

Accept — within tolerance

Answer

1.2503" falls within the allowable range of 1.2497"–1.2503", so the part is acceptable.

Question 2

Which surface finish parameter describes the average height of surface irregularities measured from the mean line?

Accepted Answer

Ra

Answer

Ra (arithmetic average roughness) is the average absolute deviation of the surface profile from the mean line.

Question 3

A technician uses a sine bar with a 5.000" center-to-end distance and needs to set a 15° angle. What gauge block stack height is required?

Accepted Answer

1.294"

Answer

Height = L × sin(θ) = 5.000 × sin(15°) = 5.000 × 0.2588 ≈ 1.294".

Question 4

On a CMM report, the term 'true position' refers to:

Accepted Answer

The diameter of the tolerance zone within which the feature axis must lie

Answer

True position tolerance defines the cylindrical (or circular) zone within which the feature's axis or center point must fall.

Question 5

What is the primary reason gauge blocks are 'wrung' together rather than stacked loosely?

Accepted Answer

Molecular adhesion eliminates the air gap and maintains accuracy

Answer

Wringing creates a near-zero air gap through molecular adhesion and surface tension, keeping the combined height accurate to millionths of an inch.

(CNC) Computer Numerical Control Machinist Technical Practice Test