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Jigs and fixtures: purpose and differences

Short answer

A jig guides the tool via bushes (e.g., plate jig); a fixture only locates and holds work without guiding (e.g., milling vice). Purposes include repeatable positioning, eliminating marking out, and faster production with improved accuracy. Jigs are light, for drilling; fixtures are heavy, for milling, turning, etc.

What are jigs and fixtures? State their purposes and advantages. Differentiate between a jig and a fixture with examples.

A jig is a work-holding device that holds and locates the work and also guides the cutting tool (through bushes). A fixture holds and locates the work and sets the tool position, but does not guide the tool.

Purposes and advantages

  • Locate and hold the work in the same position every time, so parts are interchangeable.
  • Remove the need for marking out, measuring and setting up, saving time.
  • Increase the production rate and reduce the cost per piece; allow semi-skilled operators to be used.
  • Improve accuracy and repeatability; reduce scrap.
  • Provide safe and rigid clamping; allow several tools or parts to be handled at once.
  • Make operations on difficult shapes possible.

Differences

JigFixture
Guides the tool through bushesDoes not guide the tool; the tool is set with setting blocks and feelers
Usually used for drilling, reaming, tappingUsed for milling, turning, grinding, welding, inspection
Usually light, and often not clamped to the tableHeavier, and firmly bolted to the machine table
The tool position is fixed by the bush, so no tool setting is neededThe tool must be set relative to the fixture using gauge (setting) blocks
Examples: plate jig, box jig, template jigExamples: milling vice, turning fixture, welding fixture

✓ Answer checked by Claude Opus 5.5 (high effort)

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