What is workholding?

Table clamps and zero-point systems with pallets belong to it as well; chuck and collet are the lathe forms, and a fixture is built for one part. It does two jobs: it locates the part in a known, repeatable position, and it holds it against the cutting forces without distorting it. Toolholding, such as a collet chuck gripping a cutter, is a separate subject.

What does the choice of workholding depend on?

The choice depends on the shape and stiffness of the part, the clamping faces available, the datums on the drawing, the cutting forces, access to the features, the repeatability required and the quantity. A prismatic part is often located on the 3-2-1 principle: three points on one face, two against a side, one against an end. Clamping force should push the part onto those locators. Too much force distorts a flexible part, which springs back after release and loses flatness or size. Sometimes material has to be left on to clamp by, such as a clamping margin or a clamping stud.

How does workholding work in practice?

Workholding affects how long setup takes, how large the blank must be and which features can be reached in one setup. A clamping margin costs extra material and an operation to remove it. Standard workholding is quick to set up but can mean more setups; a fixture or zero-point system takes preparation and shortens setup per batch. Thin plate and plastics often sit better on vacuum than in a vice, provided cutting forces stay low and the plate seals well.

What is workholding often confused with?

Workholding is not the setup: the same workholding serves several setups, each in its own orientation. Nor is it toolholding: a collet chuck that grips a cutter holds the tool, not the part. And a fixture only locates and holds the part, whereas a jig also guides the tool.