CNC Workholding and Fixturing 2 — Questions and Answers
Question 1: What is the function of a toe clamp in CNC fixturing?
- To hold the workpiece from above by stepping over its edge (Correct answer)
- To clamp the workpiece from the side using a cam mechanism
- To anchor the fixture plate to the machine table
- To locate a round workpiece against a V-block
Correct answer: To hold the workpiece from above by stepping over its edge
Toe clamps step over the edge of a workpiece and apply downward clamping force from above, holding the part to the table or fixture plate.
Question 2: Which type of chuck jaw is used when machining a second operation (Op 2) that must be centered on a previously machined bore?
- Hard raw jaws
- Soft bored jaws (Correct answer)
- Step jaws
- Pie jaws
Correct answer: Soft bored jaws
Soft bored jaws are bored to match the part's previously machined diameter, providing precise centering and even clamping force for Op 2 machining.
Question 3: What is a major advantage of using a zero-point clamping system in CNC machining?
- Eliminates the need for coolant during setup
- Allows sub-minute workpiece changes with pre-set repeatability (Correct answer)
- Reduces spindle speed requirements for heavy cuts
- Enables cutting without G-code offsets
Correct answer: Allows sub-minute workpiece changes with pre-set repeatability
Zero-point clamping systems allow palletized workpieces or fixtures to be located and clamped within seconds with repeatability under 0.005mm.
Question 4: When clamping a thin, flat workpiece on a CNC mill table, why is vacuum fixturing preferred?
- It provides higher clamping force than mechanical clamps
- It holds the part without deforming it and keeps the top surface clear (Correct answer)
- It works equally well on all materials including non-ferrous metals
- It eliminates the need for work coordinate offsets
Correct answer: It holds the part without deforming it and keeps the top surface clear
Vacuum fixturing applies uniform distributed force across the part's bottom surface, preventing distortion of thin parts while keeping the entire top surface accessible.
Question 5: In CNC turning, why is it critical that the cutting tool is set exactly at center height?
- To match the programmed RPM with the correct SFM
- To prevent rubbing on the tool flank and ensure correct cutting geometry (Correct answer)
- To allow the coolant to flow over the tool correctly
- To align with the chuck jaw reference marks
Correct answer: To prevent rubbing on the tool flank and ensure correct cutting geometry
When the tool is not at center height, the effective rake and clearance angles change, causing rubbing rather than cutting, increased forces, and poor surface finish.
Question 6: What is the purpose of using strap clamps with step blocks in CNC milling setups?
- To create a reference surface for probing
- To apply downward clamping force to odd-shaped or large workpieces (Correct answer)
- To set the tool length offset automatically
- To prevent coolant from entering the T-slots
Correct answer: To apply downward clamping force to odd-shaped or large workpieces
Strap clamps with step blocks provide versatile downward clamping for irregularly shaped or large parts that cannot fit in a standard vise.
CNC Workholding and Fixturing 2
What is the function of a toe clamp in CNC fixturing?