Setup

A setup is the specific way a part is positioned, oriented and held (fixtured) on a machine for one or more operations. A part typically needs a new setup whenever a face that must be machined is not reachable from the current orientation, or when the required accuracy between features can only be held by keeping them in one fixturing.

Why the number of setups matters for cost

Each setup costs time and, on small batches, that time often dominates the price. See setup time and run time for how that cost is separated from the cutting itself.

How the number of setups is determined

Not stated directly; it follows from which faces need machining, the datums and geometric tolerances that must be held together, and what a specific machine and fixture can reach in one orientation.

Common mistakes

Assuming a part needs exactly one setup because it looks simple. A tolerance between two faces that are only reachable from different orientations can force a second setup even on an otherwise straightforward part.

Is a setup the same as fixturing?

Fixturing is how the part is physically held; a setup is the broader concept of position, orientation and fixturing together for a given group of operations.

Why does a part need more than one setup?

Because not every face can be reached, or measured accurately relative to a datum, from a single orientation.

Does more setups always mean more cost?

Usually yes, since each one adds time and a risk of misalignment between setups.