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 × D) / (π × 12)

Answer

RPM = (π × D × SFM) / 12

Answer

RPM = (SFM × D × 12) / π

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

The rotational speed of the spindle in RPM

Answer

The depth of material removed per pass

Answer

The surface speed at the cutting edge

Question 3

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

Accepted Answer

Higher cutting speed (SFM)

Answer

Excessive coolant flow volume

Answer

Lower workpiece material hardness

Answer

Reduced depth of cut

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

Total weight of chips produced per machining cycle

Answer

Feed rate divided by the number of flutes

Answer

The cutting force measured in pounds per tooth

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

Decrease significantly due to aluminum's ductility and tendency to smear

Answer

Stay the same because spindle speed is set by the machine

Answer

Be determined solely by the coolant type being used

Question 6

What problem most commonly results from setting the milling feed rate too low?

Accepted Answer

Tool rubbing rather than cutting, causing work hardening and increased tool wear

Answer

Tool breakage from excessive chip load on each tooth

Answer

Vibration chatter from resonance at low feed

Answer

Rapid chip accumulation in the cutting zone

Question 7

In end milling, 'axial depth of cut' (ADOC) refers to:

Accepted Answer

How far the cutting flutes engage the workpiece along the tool's Z-axis

Answer

The width of the cut measured perpendicular to the tool axis

Answer

The distance between successive parallel tool passes

Answer

The total depth of a finished pocket