Practice Test Geeks(CNC) Computer Numerical Control Machinist Technical Practice Test
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Precision Measurement & Quality Control Flashcards

7 cards from real CNC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Precision Measurement & Quality Control flashcards as text

  1. When reading a vernier caliper, the main scale reads 1.400" and the vernier scale's 8th line aligns. With a 25-division vernier (least count 0.001"), what is the measurement?

    Answer: 1.408"

    The 8th vernier line aligned means 8 × 0.001" = 0.008" is added to the 1.400" main scale reading, giving 1.408".

  2. A process capability index Cp = 1.67 but Cpk = 0.85. What does this indicate about the process?

    Answer: The process spread is acceptable but the process is off-center

    Cp > 1.33 means the process spread fits within the tolerance, but Cpk < 1.00 means the process is shifted significantly off the target center.

  3. An optical comparator projects a magnified shadow of a part onto a screen. If the screen magnification is 20× and the shadow edge deviates 0.100" from the overlay line, what is the actual part deviation?

    Answer: 0.005"

    Actual deviation = screen deviation ÷ magnification = 0.100" ÷ 20 = 0.005".

  4. In GD&T, the Maximum Material Condition (MMC) for a shaft of 1.000" ±0.005" is:

    Answer: 1.005"

    MMC for an external feature (shaft) is its largest allowable size, which is the nominal plus the tolerance: 1.000" + 0.005" = 1.005".

  5. A hardness tester leaves a Rockwell C (HRC) indentation. HRC is used rather than HRB because the part:

    Answer: Is a hardened steel above the HRB scale range

    The Rockwell C scale uses a diamond cone indenter and 150 kgf load, making it suitable for hard steels above the HRB practical range (above ~100 HRB).

  6. A CMM probe qualification (calibration sphere) is performed before each measurement session primarily to:

    Answer: Determine the exact probe tip diameter and center offset to compensate measurements

    Probing the reference sphere allows the CMM software to precisely calculate the ruby stylus tip's diameter and spatial offset, correcting all subsequent measurements.

  7. Which measurement tool is BEST suited for checking the pitch diameter of an external thread?

    Answer: Three-wire method with a micrometer

    The three-wire method — inserting precisely sized wires into thread grooves and measuring over them with a micrometer — gives the most accurate direct pitch diameter measurement.