Workholding and Fixturing Flashcards

What is the primary purpose of a CNC vise stop (work stop)?

Answer: To provide a repeatable datum for part positioning

A work stop provides a consistent reference surface so that each part loaded into the vise starts from the exact same position, ensuring repeatability.

When using a machine vise, why should the workpiece be tapped down with a mallet after initial tightening?

Answer: To seat the part firmly against the parallels and prevent lifting

Tapping the part down ensures it is fully seated against the parallels, preventing it from lifting due to upward clamping forces during machining.

What type of workholding device uses a magnetic field to hold ferrous workpieces without mechanical clamping?

Answer: Magnetic chuck

A magnetic chuck uses electromagnetic or permanent magnetic force to hold ferrous (iron-containing) workpieces flat against its surface without obstructing the top.

In modular fixturing, what is the primary benefit compared to dedicated fixtures?

Answer: Reconfigurability for multiple part families without building new fixtures

Modular fixturing components can be disassembled and reconfigured for different parts, reducing the need to build expensive dedicated fixtures for each job.

What is the 3-2-1 locating principle used for in CNC workholding?

Answer: Constraining all six degrees of freedom with the minimum number of contact points

The 3-2-1 principle uses three points on the primary plane, two on the secondary, and one on the tertiary to fully constrain a part's six degrees of freedom.

Why should parallels used in a vise be matched pairs of the same height?

Answer: To keep the workpiece level and prevent rocking during machining

Matched parallels of equal height ensure the workpiece sits level and stable, preventing rocking that would cause inaccurate cuts and potential part movement.