CNC Work Holding & Fixturing 2 — Questions and Answers
Question 1: What is the primary advantage of a hydraulic vise over a standard mechanical vise in CNC machining?
- Lower cost per unit
- Consistent and repeatable clamping force (Correct answer)
- Lighter weight for easy repositioning
- Compatible with more workpiece materials
Correct answer: Consistent and repeatable clamping force
Hydraulic vises apply consistent, repeatable clamping force that reduces part-to-part variation and operator error.
Question 2: A sine bar is used in fixturing primarily to:
- Measure surface roughness
- Set precise angular orientations of a workpiece (Correct answer)
- Check parallelism of two surfaces
- Locate a part relative to the spindle centerline
Correct answer: Set precise angular orientations of a workpiece
A sine bar uses precision gauge blocks and trigonometry to set exact angular positions for workpieces during machining or inspection.
Question 3: Which clamping method is most appropriate when a workpiece must be machined on all four vertical sides without re-fixturing?
- Step clamps on all sides
- A tombstone fixture on a horizontal machining center (Correct answer)
- A standard 3-jaw chuck
- Double-sided tape on a surface plate
Correct answer: A tombstone fixture on a horizontal machining center
A tombstone fixture mounted on a horizontal machining center allows B-axis indexing to access multiple faces in one setup.
Question 4: What does 'pull stud' retention refer to in CNC toolholding?
- A stud that pulls the collet nut tight
- The mechanism that draws and locks the toolholder into the spindle taper (Correct answer)
- A set screw that prevents tool pullout from the holder
- A retention knob used on manual mills only
Correct answer: The mechanism that draws and locks the toolholder into the spindle taper
A pull stud (retention knob) is threaded into the toolholder shank and is gripped by the spindle drawbar to secure the toolholder in the machine spindle.
Question 5: When using parallels in a vise, their purpose is to:
- Increase the clamping force on the workpiece
- Elevate the workpiece so it sits above the vise jaws for full feature access (Correct answer)
- Prevent the vise from deflecting under cutting loads
- Align the vise jaw to the machine axis
Correct answer: Elevate the workpiece so it sits above the vise jaws for full feature access
Parallels raise the workpiece above the vise jaw top surface, exposing more of the part and allowing the cutter to clear the jaws.
Question 6: A modular fixturing system's key advantage over dedicated fixtures is:
- Lower initial tooling cost for high-volume production
- Rapid reconfiguration for different part geometries (Correct answer)
- Greater rigidity for heavy interrupted cuts
- Automatic workpiece loading capability
Correct answer: Rapid reconfiguration for different part geometries
Modular fixtures use standardized, reusable components that can be quickly rearranged to hold different parts, reducing lead time for new setups.
Question 7: Which of the following best describes 'nesting' in CNC fixturing?
- Stacking multiple fixtures on top of each other
- Using a locating pocket or feature that precisely positions the workpiece (Correct answer)
- Arranging multiple vises in a grid pattern on the table
- Threading a part onto a mandrel for turning operations
Correct answer: Using a locating pocket or feature that precisely positions the workpiece
Nesting involves a machined or cast recess in the fixture that the workpiece drops into, providing accurate repeatable location.
CNC Work Holding & Fixturing 2
What is the primary advantage of a hydraulic vise over a standard mechanical vise in CNC machining?