CNC Speeds, Feeds & Machining Parameters 3

Question 1

What is the purpose of specifying a 'dwell' (G04) command in a CNC boring cycle?

Accepted Answer

To pause spindle rotation at the bottom of the bore for a timed period to improve finish

Answer

A G04 dwell at the bottom of a bore allows the tool to complete a full revolution, cleaning up any feed lines and improving roundness and finish.

Question 2

When machining stainless steel (304 SS), which approach is preferred to reduce work hardening?

Accepted Answer

Continuous cuts with adequate chip load to stay below the work-hardened layer

Answer

Stainless steel work-hardens quickly; maintaining continuous, sufficiently deep cuts keeps the tool cutting below the already-hardened surface layer.

Question 3

In high-speed machining (HSM), which strategy reduces radial load while maintaining material removal rate?

Accepted Answer

Trochoidal or circular arc tool paths with low RDOC and high ADOC

Answer

Trochoidal tool paths use low radial engagement but high axial depth, distributing heat over the entire flute length and reducing peak load.

Question 4

What does 'tool life' in Taylor's tool life equation primarily depend on?

Accepted Answer

Cutting speed (SFM) as the dominant variable

Answer

Taylor's equation (VT^n = C) shows that cutting speed is the dominant variable — doubling SFM dramatically reduces tool life.

Question 5

When calculating feed rate (IPM) for a milling operation, which variables are needed?

Accepted Answer

RPM, number of flutes, and chip load (IPT)

Answer

Feed rate (IPM) = RPM × Number of Flutes × Chip Load (IPT), which directly links table feed to the number of cutting edges and desired chip thickness.

(CNC) Computer Numerical Control Machinist Technical Practice Test

(CNC) Computer Numerical Control Machinist Technical Practice Test

CNC Speeds, Feeds & Machining Parameters 3