CNC Speeds, Feeds & Machining Parameters 2

Question 1

If a CNC lathe is running at 800 RPM and the workpiece diameter is 2.0 inches, what is the approximate surface footage (SFM)?

Accepted Answer

About 420 SFM

Answer

SFM = (RPM × Diameter × π) / 12 = (800 × 2.0 × 3.14159) / 12 ≈ 419 SFM, which rounds to about 420 SFM.

Question 2

What does 'radial depth of cut' (RDOC) refer to in a milling operation?

Accepted Answer

The stepover distance of the cutter across the workpiece

Answer

Radial depth of cut (RDOC) is the lateral engagement of the cutter, measured perpendicular to the spindle axis, often expressed as a percentage of cutter diameter.

Question 3

Which machining parameter most directly affects tool deflection and dimensional accuracy in CNC milling?

Accepted Answer

Tool stick-out length

Answer

Excessive tool stick-out increases leverage on the cutter, magnifying deflection forces and causing dimensional error and chatter.

Question 4

When using a constant surface speed (CSS) mode on a CNC lathe, what happens to RPM as the tool moves toward the center of the workpiece?

Accepted Answer

RPM increases to maintain SFM

Answer

As diameter decreases toward center, the control raises RPM automatically to keep surface feet per minute constant.

Question 5

Which of the following best describes 'climb milling' compared to 'conventional milling'?

Accepted Answer

The cutter rotates in the same direction as the feed, starting with thick chips

Answer

In climb milling the cutter rotates in the feed direction, starting with a thick chip that thins to zero, reducing heat and improving surface finish.

(CNC) Computer Numerical Control Machinist Technical Practice Test

(CNC) Computer Numerical Control Machinist Technical Practice Test

CNC Speeds, Feeds & Machining Parameters 2