– Form Metrology Basics
Assessment of geometric features such as roundness, flatness, and straightness to ensure part conformance.
- Roundness and cylindricity: measure how closely a part’s shape matches a true circle or cylinder.
- Intrinsic datum methods use the part’s own geometry as a reference to assess roundness.
- Micrometers and Vernier calipers: check basic diameters
- V-block method: detect roundness errors by rotating the part in a V-shaped fixture
- Rotation between centers: detect form deviations using a dial indicator as a part rotates.
- Extrinsic datum methods: use a precision spindle as a reference.
- Rotating spindle method: the part remains stationary while a high-precision spindle rotates the measuring probe to capture circularity.
- Rotating part method: the part is rotated on a precision spindle while the probe remains fixed, to detect roundness and form deviations.
- Intrinsic datum methods use the part’s own geometry as a reference to assess roundness.
- Straightness/Flatness: examine deviation from an ideal straight line or flat plane.
- Straight edge artifact: compare the test surface visually or with feeler gauges against a precision straight edge.
- Electronic Level: measure angular deviation to assess flatness or inclination.
- Auto collimator: reflected light beams detect angular deviations across a surface.
- Surface profile instrument with a long travel range: capture height data across a wide path to evaluate form errors.
- Coordinate measuring machine: construct best-fit lines or planes from sampled data to analyze straightness or flatness.