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More Typical Design Cases

Additional worked examples: boring, gear shaping, grinding and CNC milling fixtures. Each case lists the datum scheme, locator selection, clamping strategy and measured results.

1Boring Fixture for Gearbox Housing

Bore a Ø80H7 hole in a cast iron gearbox housing, tolerance 0.03 mm, production batch 500/year.

  1. Locate on the machined base flange (3-2-1) and one side face for rotational orientation.
  2. Clamp with four hydraulic swing clamps on the top flange, 8 kN each, directed toward the base.
  3. Guide the boring bar with a fixed bushing in the fixture wall; bushing ID 80H6, 25 mm long.
  4. Fixture body: welded steel box, 40 mm wall, stress-relieved, ground base. Key to machine table T-slots.
  5. Result: bore position within 0.015 mm, roundness 0.008 mm, 3.5 min cycle time.
boring bar fixed bushing guides the bar in the wall
The welded fixture cost 40% less than a cast iron one and passed the 500-piece first-article inspection.

2Gear Shaping Fixture

Shape teeth on a Ø120 mm spur gear blank, module 3, 40 teeth, accuracy grade 7, batch 2000/year.

  1. Locate on the gear bore (30H6) with an expanding mandrel; face datum on the hub shoulder.
  2. Clamp with a light spring-loaded washer — 300 N axial force only, to avoid gear distortion.
  3. Mount the mandrel between centers in the gear shaper; drive the mandrel with a dog plate.
  4. Index the gear on the shaper's built-in indexing mechanism; fixture concentricity within 0.005 mm.
  5. Result: gear runout 0.02 mm, lead error 0.01 mm, 2.8 min cycle time per gear.
centers expanding mandrel locates on the bore
Excessive clamping force distorts the gear blank, causing tooth spacing error after cutting.

3Grinding Fixture for Thin Plates

Surface grind a 200×150×5 mm steel plate flat to 0.01 mm, parallel within 0.005 mm.

  1. Clean the magnetic chuck surface; demagnetize the plate before loading.
  2. Place the plate on the magnetic chuck with a 0.02 mm shim under one edge to pre-stress against distortion.
  3. Engage the magnetic chuck; moderate magnetic force to avoid plate deformation.
  4. Grind with a 46-grit wheel, 0.005 mm depth per pass, heavy coolant flow. Flip and re-grind the opposite side.
  5. Result: flatness 0.008 mm, parallelism 0.004 mm, 12 pieces per hour.
grinding wheel shim pre-stresses the plate on the chuck
For non-magnetic materials (aluminum, stainless, titanium), use a vacuum chuck with 0.06 MPa vacuum pressure.

4CNC Milling Fixture for Complex Aluminum Housing

Machine all features on a 250×180×120 mm aluminum die-cast housing in one setup, tolerance ±0.05 mm.

  1. Locate on three cast pads (machined first) for the primary datum, two pin holes for secondary/tertiary.
  2. Clamp with four pneumatic swing clamps, 2 kN each, with pressure switches for clamp confirmation.
  3. Fixture base: 30 mm aluminum plate with hardened steel locator bushings and wear pads.
  4. Open design with wide chip clearance; no tool interference for side-milling and drilling operations.
  5. Pallet-mounted for quick load/unload; 3.2 min manual load, 12 min machining cycle, 3 shifts unattended.
swing clamps pads + pins locate; pallet carries the fixture
Single-setup CNC fixturing eliminated 3 previous setups, reducing total cycle time by 55%.