Precision Measurement & Quality Control Flashcards

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?

Answer: Accept — within tolerance

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

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

Answer: Ra

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

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?

Answer: 1.294"

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

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

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

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

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

Answer: Molecular adhesion eliminates the air gap and maintains accuracy

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

A dial test indicator reads 0.0015" TIR when sweeping a turned shaft in V-blocks. This reading represents:

Answer: The total runout from high to low reading

TIR (Total Indicator Reading) is the full swing from the lowest to highest reading, equal to twice the eccentricity.

Which material is the ANSI standard for gauge blocks used in calibration labs?

Answer: Chromium steel (grade A2 or better)

ANSI/ASME B89.1.9 specifies chromium steel as the standard material for gauge blocks, offering hardness, stability, and low thermal expansion.