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Typical Fixture Design Cases

Worked examples showing how locating and clamping principles are applied. Each case lists the datum scheme, locator selection and clamp strategy.

Design Process (work order)

  1. Study the drawing: identify datums (A, B, C) and critical tolerances.
  2. Select locating points on the datum features (3-2-1 or pins).
  3. Choose clamps and direct forces toward the locators.
  4. Size clamps from cutting force / friction with a safety factor.
  5. Check loading, chips, coolant, tool path and machine interface.
  6. Review with the checklist before manufacturing.

Worked Examples

1Case 1 — Plate drilling jig

Drill 4 holes in a flat steel plate. Datums: bottom face (A) + two reamed holes.

  • Locating: 3 pads on face A, round pin in hole 1, diamond pin in hole 2.
  • Clamping: two strap clamps pressing onto the pads, not over unsupported area.
  • Guiding: hardened drill bushings close to the surface for accurate hole position.
  • Chips: extended bushings break chips; openings for coolant and chips.

2Case 2 — Milling fixture for a cast bracket

Mill the mounting face and two side faces of a cast iron bracket. Cast surfaces are inaccurate, so locate on machined pads.

  • Locating: 3-2-1 on three machined pads (cast datum points).
  • Clamping: pneumatic block clamps for fast loading in a batch.
  • Support: heavy support under the milled area; clamp forces toward the table.
  • Chips: slots and openings let chips fall clear of the locators.

3Case 3 — Turning fixture (faceplate)

Turn a part that cannot be chucked on the O.D. — a thin ring mounted on a faceplate.

  • Locating: register bore + face on the faceplate, centered via a tapered pilot.
  • Clamping: three evenly spaced swing clamps, balanced arrangement.
  • Balancing: balanced fixture to avoid vibration at speed.
  • Driving: clamp force must resist cutting torque; check friction drive capacity.

4Case 4 — Inspection fixture

Gauge a machined part against the drawing datums without clamping distortion.

  • Locating: rest on datum pads and pins; low clamping force.
  • Checking: pins or dial indicators at critical features.
  • Material: aluminium or hardened steel; lightweight and stable.
These cases are starting points, not complete drawings. Always verify cutting forces, clamp capacity and tool clearance for your actual part.