Jigs and Fixtures: Introduction and Purpose

Jigs and fixtures are essential to working holding and tool holding devices in industries. These devices facilitate clamping of the workpiece on the machine tool in correct relationship with the cutting tool.

Jigs and fixtures are often used in interchangeably and sometimes in pairs, but there is a difference between two terms jigs and fixtures.

Jig:

Jig(tool) is defined as a device which holds and positions the work, locates or guides the cutting tool about the workpiece and usually is not fixed to the machine table.
Jigs
Jigs are used for performing the operations of drilling, reaming, tapping and counter boring.

Fixture:

Fixture(tool) is a work holding device which only holds and positions the work but does it in itself guide locate or position the cutting tool. The setting of the device is done by machine is done by machine adjustment and a setting block or by using slip gauges. A fixture is bolted or clamped to the machine table and is usually heavy in construction.
Fixture or gripping

Pincer grip for material testing in tensile tests. Image source: Wikimedia Commons

Fixtures are designed for specific purposes of machining operations, such as turning, milling, grinding, shaping, planning, and boring operations.

The purpose of using jigs and fixtures:

  • To reduce the cost of production, By using them, they eliminate the laying out of work and setting up of the tools.
  • To increase the production rate.
  • To ensure high accuracy of parts produced without any manufacturing defects.
  • To provide for interchangeability.
  • To ensure heavy and complicated shaped parts are to be machined easily.
  • Reduce quality control expenses.
  • Increased versatility of the machine tool.
  • Their use partially automates the machine tool.
  • To provide safety at the work point.

Jigs and Fixtures differ in the following ways:

S.no Jigs Fixtures
1 Jig is a work holding device that holds, supports and locates the workpiece and guides the cutting tool for a specific operation. Fixture is a work holding device that holds, supports and locates the workpiece for a specific operation but does not guide the cutting tool
2 Jigs are not clamped to the drill press table unless large diameters to be drilled and there is a necessity to move the jig to bring one each bush directly under the drill. Fixtures should be securely clamped to the table of the machine upon which the work is done.
3 The jigs are special tools particularly in drilling, reaming, tapping and boring
operation.
Fixtures are specific tools used particularly in milling machine, shapers and slotting machine.
4 Gauge blocks are not necessary. Gauge blocks may be provided for effective handling.
5 Jigs are lighter in construction. Fixtures are heavier in construction.
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