Purpose of Jigs and Fixtures
Jigs guide cutting tools (e.g., drill jigs), while fixtures hold workpieces in position. Both ensure consistent part location, reduce setup time, and improve machining accuracy.
6-Point Location Principle
A workpiece has 12 degrees of freedom (6 positive, 6 negative). The 3-2-1 locating principle uses 6 fixed points to restrain all 6 positive directions: 3 points on the primary datum plane, 2 on the secondary, and 1 on the tertiary.
Clamping Principles
- Clamping force must oppose cutting forces
- Clamps should not distort the workpiece
- Loading and unloading should be quick
- Swarf (chips) should not interfere with locating surfaces
Common Fixture Types
- Dedicated fixtures - For a specific part (high volume)
- Modular fixtures - Reconfigurable (low/medium volume)
- Vise fixtures - Standard workholding for prismatic parts
- Pallet systems - For automated FMS lines
- Tombstone fixtures - For horizontal machining centers