CNC Basics 5

Question 1

What is 'chatter' in CNC machining and what is its primary cause?

Accepted Answer

Vibration between the tool and workpiece caused by resonance in the cutting system

Answer

Chatter is self-excited vibration where the cutting forces feed energy into the machine-tool-workpiece resonant frequency, producing poor surface finish and accelerated tool wear.

Question 2

Which axis on a standard vertical machining center (VMC) controls the up-and-down movement of the spindle?

Accepted Answer

Z-axis

Answer

On a VMC, the Z-axis is the spindle axis and controls vertical (up and down) movement, determining depth of cut.

Question 3

What is the recommended action when a CNC program encounters a tool that has exceeded its programmed tool life?

Accepted Answer

Replace or offset to a sister tool before resuming machining

Answer

Most CNC controllers support sister tool management, which swaps to an identical spare tool when the original exceeds its life limit, preventing scrap parts.

Question 4

What does 'surface feet per minute' (SFM) describe in CNC cutting?

Accepted Answer

The velocity at which the cutting edge moves past the workpiece surface

Answer

SFM (or surface meters per minute in metric) measures the tangential speed of the cutting edge relative to the workpiece, and is the primary parameter for selecting RPM.

Question 5

Why is it important to verify a CNC program using simulation software before running it on the machine?

Accepted Answer

It allows detection of tool collisions, gouges, and incorrect tool paths without risking the machine or workpiece

Answer

Simulation visually replays the tool path in a virtual environment, revealing crashes, gouges, missed features, and other errors before any metal is cut.

CNC - Cutting Practice Test

CNC - Cutting Practice Test

CNC Basics 5