Fixture Design


Reading Assignment

Optional Reading

Fixture Examples


Lathe Fixtures

A lathe fixture must account for factors associated with a turning workpiece. Counterbalances may be necessary. Fixtures may attach directly to the spindle, or be held in the faceplate, collet or chuck already on the machine. Fixtures must clear any tooling or machine parts.

As with any machining setup, rigidity is fundamental to success. Always fixture components as rigidly as possible.

Some operations that are performed on a lathe (particularly boring) can be done with better success on a mill.

Below is an excerpt from Tool Design, MET331, Dr Simin Nasseri, Southern Polytechnic State University

  • Since lathe fixtures are designed to rotate, they should be as lightweight as possible.
  • Lathe fixtures must be balanced. While perfect balance is not normally required for slow

speed turning operations, high rotational speeds require the fixture to be well-balanced. In
most fixtures, balance is achieved by using counterweights positioned opposite the
heaviest part (or area) of the workpiece.

  • Projections and sharp corners should be avoided, since these areas will become almost

invisible as the tool rotates and they could cause serious injury.

  • Parts to be fixtured should, whenever possible, be gripped by their largest diameter or

cross section.

  • The part should be positioned in the fixture so that most of the machine operation can be

performed in the first fixturing.

  • Clamps should be positioned on rigid surfaces or areas before and after machining.
  • Clamping over an area to be bored to a very thin-wall thickness could cause the part to

warp or deform, thus causing the hole to be bored incorrectly.

  • As with other fixtures, some means of cutter setting should be incorporated into the

design. However, since the workholder will be rotating, this setting device should later be

  • Whenever possible, standard lathe accessories should be adapted in the design of turning

fixtures. Lathe faceplates are an ideal method to mount large fixtures. Likewise, a standard
lathe chuck, or collets, can and should be modified for many fixturing applications.

Swing-up stops
Micrometer stops.

Plate Fixture

A plate fixture is useful when fixturing for 2-D feature placement (holes, slots, tapping, etc.). They are used primarily when only one face of the part will be machined.

Multipart or Multistation Fixture

Setup Gage
Set Block
Using a gage block to set tool.

Micrometer stop

Welding Fixtures

Welding fixtures can greatly increase the productivity of a welding operation. Aluminum is and ideal material for welding fixtures as it conducts electricity well and is light weight. Fixtures may also be constructed from steel or even wood (take fire precautions!).

Bicycle Frame Jig (Fixture)

MDF Bicycle Frame Jig (kickstarter)

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