CNC Cutting Parameters and Speeds/Feeds

Question 1

What is the correct formula for calculating spindle speed (RPM) from cutting speed (SFM) and tool diameter (D in inches)?

Accepted Answer

RPM = (SFM × 12) / (π × D)

Answer

RPM = (SFM × 12) / (π × D) converts linear cutting speed to rotational speed by accounting for the tool's circumference in inches.

Question 2

In CNC milling, what does 'feed rate' primarily describe?

Accepted Answer

The linear distance the cutting tool travels per unit of time (inches per minute)

Answer

Feed rate in milling is typically expressed as inches per minute (IPM), describing how fast the cutter moves through the workpiece material.

Question 3

Which factor most directly accelerates tool wear rate in CNC cutting?

Accepted Answer

Higher cutting speed (SFM)

Answer

Higher cutting speeds generate more heat at the cutting edge, which exponentially accelerates tool wear according to Taylor's tool life equation.

Question 4

What is 'chip load' (feed per tooth) in CNC milling?

Accepted Answer

The amount of material each cutting edge removes per revolution

Answer

Chip load (feed per tooth) is the thickness of the chip each flute removes per revolution, calculated as IPM / (RPM × number of flutes).

Question 5

When switching from machining steel to aluminum, cutting speeds (SFM) should typically:

Accepted Answer

Increase significantly because aluminum is much softer and thermally conductive

Answer

Aluminum can be machined at 3–5× higher SFM than steel because it is softer, has excellent thermal conductivity, and does not require the same heat management.

CNC - Cutting Practice Test

CNC - Cutting Practice Test

CNC Cutting Parameters and Speeds/Feeds