Work Holding & Fixturing Flashcards

What is the main reason that fixture clamps should never be placed over unsupported areas of a thin-walled workpiece?

Answer: The clamp force will elastically deflect or permanently deform the part wall

Without a support directly beneath it, a thin wall will deflect under clamping load, leading to dimensional errors or permanent deformation after release.

A 'pallet changer' (APC) on a horizontal machining center improves productivity primarily by:

Answer: Allowing one pallet to be loaded/unloaded while the machine cuts on the other

The automatic pallet changer lets an operator set up the next part on the idle pallet while the spindle is cutting, nearly eliminating non-productive load/unload time.

Which type of locating pin is preferred when a fixture must accommodate slight variation in hole-to-hole distance between the part and the fixture?

Answer: Diamond (relieved) pin

A diamond pin is relieved on two sides so it can compensate for tolerance stack-up between two hole locations while still constraining rotation.

In a tombstone setup, the term 'balanced loading' refers to:

Answer: Distributing parts on opposite sides of the tombstone so the combined workpiece mass is balanced for rotation

Balanced loading places heavier workpieces on opposing faces to minimize dynamic imbalance when the rotary axis indexes at high speed.

A 'dead-length' collet system in a CNC lathe differs from a standard collet in that it:

Answer: Clamps the workpiece without axial movement, maintaining a fixed Z-datum position

Dead-length collets expand/contract radially without moving the workpiece axially, preserving the part's Z-axis position and eliminating datum shift.

When machining a part in a vise and the solid jaw (fixed jaw) deflects outward during clamping, the most likely cause is:

Answer: Worn or loose vise mounting bolts allowing the vise body to flex

If mounting bolts are loose or worn, clamping force creates a moment that deflects the vise body, causing the fixed jaw to splay outward and compromising accuracy.

What is the purpose of applying a 'torque specification' when tightening fixture clamp bolts in precision CNC work?

Answer: To ensure consistent and repeatable clamping force from part to part

Using a calibrated torque specification ensures that every part in a production run is clamped with the same force, reducing dimensional variation caused by workpiece deflection differences.