Machining feeds and speeds

Question 1

What diameter is used in RPM calculations when TURNING on a lathe?

Answer 1

Work Piece Diameter

Question 2

What diameter is used in RPM calculations when DRILLING on a lathe?

Answer 2

Drill Bit Diameter

Question 3

What is the formula for spindle RPM?

Answer 3

RPM = CSx4/D

Question 4

What should your lathe speed be for rough cuts?

Answer 4

0.015”/rev (0.38mm/rev)

Question 5

What should your lathe speed be for finishing cuts?

Answer 5

0.007”/rev (0.13mm/rev)

Question 6

What diameter is used in RPM calculations when milling?

Answer 6

Diameter of the tool

Question 7

What is the Feed formula for Milling? (inches per minute)

Answer 7

Number of cutter teeth x Feed per Tooth x RPM

Example:

0.5” Diameter 2 flute end mill cutting
Aluminum

Spindle RPM = 500 x 4 /0.5 = 4000 RPM 0.5

Feed Rate = 2 x 0.011 x 4000 = 88 Inches/min

Question 8

What is the difference between calculating lathe RPM vs milling RPM?

Answer 8

Lathe RPM is calculated by the diameter of the work piece, milling RPM is the tool diameter.

Question 9

What is the formula for milling feed rate?

Answer 9

F = R x T x rpm

F = Feed Rate in inches per min
R = Feed per tooth per revolution
T = Number of teeth on cutter

Feed rate = Feed per tooth per rev x Teeth x rpm

these are calculated MAXIMUMS

Question 10

How should you set multiple teeth on a fly cutter?

Answer 10

Use a dial indicator to ensure all teeth are set to the same height for consistent cutting.

Question 11

What is the formula for calculating Milling feed rate?

Answer 11

Feed Rate (in./min) = R x T x rpm

R = Feed per tooth per revolution
T = Number of teeth

Question 12

What are the cutting speeds (SPFM) for aluminum, steel and brass?

Answer 12

Aluminum: 200-300
Steel: 100
Brass: 100