Explanation:

The 3-2-1 principle of fixture design is a common method used in manufacturing to ensure accurate and consistent positioning of workpieces during machining or assembly processes. It consists of three stages of locating and clamping the workpiece, each with a different number of degrees of freedom.

1. 3 - Locators on the primary datum face:
The first stage of the 3-2-1 principle refers to the number of locators placed on the primary datum face of the workpiece. The primary datum face is the reference surface from which all other measurements and positions are determined. By using three locators, the workpiece can be securely positioned and prevented from moving in three dimensions. These locators typically consist of pins, dowels, or other protrusions that fit into corresponding holes or slots in the fixture.

2. 2 - Clamps required:
The second stage of the principle refers to the number of clamps required to hold the workpiece in place. Once the workpiece is accurately located using the three locators, it needs to be securely clamped to prevent any movement or shifting during machining or assembly operations. Two clamps are usually sufficient to hold the workpiece firmly in place. These clamps can be in the form of bolts, screws, or other fastening devices that apply pressure to the workpiece, ensuring it remains fixed in position.

3. 1 - Degrees of freedom of the workpiece:
The final stage of the principle refers to the number of degrees of freedom that the workpiece is allowed to have once it is located and clamped in the fixture. Degrees of freedom refer to the possible directions in which the workpiece can move or rotate. By using three locators and two clamps, the workpiece is effectively constrained and restricted to only one degree of freedom, usually rotation around a single axis.

Summary:
In summary, the 3-2-1 principle of fixture design states that three locators are used to accurately position the workpiece on the primary datum face, two clamps are used to securely hold the workpiece in place, and the workpiece is restricted to one degree of freedom, usually rotation around a single axis. This principle ensures that the workpiece remains stable and properly aligned during machining or assembly operations.