Workholding and Fixturing Flashcards

What does 'fixture offset' (G54–G59) allow the CNC operator to do?

Answer: Run the same program on parts fixtured in different locations on the table

Fixture offsets store the XYZ location of each workpiece origin, allowing the same program to machine parts at multiple fixture positions without reprogramming.

In high-production CNC machining, what is a pallet changer used for?

Answer: Exchanging workpiece pallets so setup occurs while the machine is cutting

A pallet changer lets operators load and unload parts on one pallet while the machine cuts parts on another, dramatically reducing machine idle time.

What is the function of a riser block in a CNC vise setup?

Answer: To elevate the workpiece so more material is exposed above the vise jaws for machining

Riser blocks are placed beneath the vise to raise it on the table, giving more clearance for longer workpieces or allowing deeper cuts below the top of the jaws.

Why is it important to indicate (sweep) a vise jaw with a dial indicator during setup?

Answer: To verify that the fixed jaw is parallel to the machine X-axis

Indicating the vise jaw ensures it is parallel to the machine's X-axis (or Y-axis), which is critical for machining square, perpendicular features.

What type of clamping error occurs when a workpiece is 'overconstrained' in a fixture?

Answer: Locating contact points compete, causing distortion or inconsistent seating

Overconstraining (or redundant locating) creates competing contact points that can distort the part or cause inconsistent seating, leading to location errors.

In CNC lathe work, what is the primary purpose of a steady rest (fixed steady)?

Answer: To support long, slender workpieces and prevent deflection during machining

A steady rest supports long, slender workpieces at a point along their length, preventing deflection and vibration that would cause chatter and dimensional errors.