CNC Speeds, Feeds & Machining Parameters

Question 1

What formula is used to calculate spindle RPM when surface footage (SFM) and tool diameter are known?

Accepted Answer

RPM = (SFM × 3.82) / Diameter

Answer

RPM = (SFM × Diameter) / 3.82

Answer

RPM = SFM / (Diameter × π)

Answer

RPM = SFM × Diameter × 3.14

Question 2

When machining 6061 aluminum with a 1/2-inch HSS end mill, which SFM range is most appropriate?

Accepted Answer

400–600 SFM

Answer

50–100 SFM

Answer

200–300 SFM

Answer

800–1000 SFM

Question 3

What effect does increasing feed rate have on chip thickness in CNC milling?

Accepted Answer

Chip thickness increases

Answer

Chip thickness decreases

Answer

Chip thickness remains the same

Answer

Chip thickness becomes variable

Question 4

The recommended starting chip load for a 1/2-inch carbide end mill in mild steel is closest to:

Accepted Answer

0.004 inch per tooth

Answer

0.001 inch per tooth

Answer

0.015 inch per tooth

Answer

0.030 inch per tooth

Question 5

What is the primary reason for reducing spindle speed when drilling deep holes?

Accepted Answer

To allow adequate chip evacuation and prevent drill breakage

Answer

To increase tool life only

Answer

To reduce power consumption

Answer

To improve surface finish at the hole bottom

Question 6

Which of the following best describes 'axial depth of cut' (ADOC) in CNC milling?

Accepted Answer

The depth the tool engages the workpiece along the spindle axis

Answer

The width of the cut measured radially from the tool center

Answer

The total length of the tool path

Answer

The feed rate in the Z-axis direction