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. A CNC operator notices that every fifth part measures 0.002" undersized even though the machine returns to the same nominal position. The MOST likely cause is:

    Answer: Backlash in the leadscrew not being compensated

    Uncompensated backlash causes the axis to consistently fall short when reversing direction, producing a systematic undersized error.

  2. A profilometer stylus tip radius of 2 µm is specified. How does a larger stylus radius affect roughness measurement?

    Answer: It underestimates Ra by not reaching into fine valleys

    A larger stylus radius cannot penetrate narrow surface valleys, causing it to underestimate the true Ra value.

  3. On a coordinate measuring machine, which datum is established first when using the 3-2-1 datum referencing method?

    Answer: The primary datum plane requiring 3 points

    The 3-2-1 method starts with the primary datum (3 points = plane), then secondary (2 points = line), then tertiary (1 point = origin).

  4. Which type of fit is specified when a shaft must slide freely in a bore with guaranteed clearance at all times?

    Answer: Clearance fit

    A clearance fit guarantees that the shaft is always smaller than the bore, ensuring free sliding motion under all tolerance conditions.

  5. A CNC machinist measures an outside diameter with a micrometer and must account for temperature. The part is steel (CTE ≈ 6.5 µin/in/°F) and measured at 85°F instead of 68°F. For a 4.000" part, the thermal growth is approximately:

    Answer: 0.00044"

    ΔL = 4.000 × 6.5×10⁻⁶ × (85−68) = 4.000 × 6.5×10⁻⁶ × 17 ≈ 0.000442".

  6. Statistical Process Control (SPC) uses control charts to monitor a process. A process is considered 'out of control' when:

    Answer: Any single point falls outside ±3 sigma control limits

    A single point beyond the ±3 sigma (3σ) control limits is the primary Western Electric rule indicating an out-of-control condition.

  7. Which GD&T symbol controls both form and orientation of a surface relative to a datum?

    Answer: Parallelism ∥

    Parallelism controls both the flatness of a surface and its angular relationship to the referenced datum plane simultaneously.