The proper selection of feeds and speeds is the most important factor in the economical application of any cutting tool.

Speed is generally known as the rate of peripheral speed in terms of surface feet per minute (SFM). SFM is usually converted to revolutions per minute as shown in formula Table 1

Feed is generally shown as feed in inches per revolution or as feed per tooth in inches (FPT).

The initial choice of feeds or speeds will be at the lower of high values of the ranges listed depending upon the following variables.

FEED
Use lower feed range for: Saws, End Mills, and Form Cutters Fine tooth cutters Frail and small cutters Light and finishing cuts Deep slots Hard to machine materials Frail set-ups	Use higher feed range for: Face and Slab milling Coarse tooth cutters Rugged cutters Heavy roughing cuts Abrasive materials East to machine materials Rigid set-ups

SPEED
Use lower feed range for: Heavy cuts Hard materials Tough materials Abrasive materials Maximum cutter life Minimum tool wear	Use higher feed range for: Light cuts Softer materials Non-metallics Frail work piece or set-up Maximum production rates Better finishes Hand feed operations Higher rakes (HSS cutters)

Modern milling cutters capable of operation at higher feeds and speeds, and removing more cubic inches of metal per minute, require greater machine rigidity and more power. Therefore it is important to ascertain that sufficient power is available to handle the desired depth and width of cut at the higher feeds and speeds.

The following formulas are suggested for the calculation on feeds and speeds plus horsepower requirements.

T = Number of teeth in cutter D = Cutter Diameter in inches RPM = Revolutions pet minute SFM = Surface feet per minute F = Feed in inches per minute

f = Feed per tooth in inches W = Width of cut d = Depth of cut HP = Motor Horsepower C = Machinability constant*

*Machinability constant values for various materials are based on removing one cubic inch of metal per minute per horsepower with 60% power efficiency at the spindle nose and a 25% allowance for cutter dulling.

Aluming, Magnesium, Dural Brass Soft Bronze, Copper Cast Iron Steel up to 150 Brinell, Malleable Iron Steel, 300 Brinell, Hard Bronze Steel, 400 Brinell

4.0 plus 2.5 2.0 1.5 .75 .6 .5

TABLE 1

.	SPEED		FEED
TYPE OF MATERIAL	HSS	CARBIDE	HSS	CARBIDE
Aluminum, Magnesium Brass & Bronze - Soft Brass & Bronze - Hard Copper Cast Iron - Soft Cast Iron - Hard	600 & Up 250 - 300 150 - 200 150 - 200 75 - 100 50 - 75	1000 & Up 1000 & Up 400 1000 & Up 250 - 350 200 - 250	.005-.025 .005-.020 .003-.010 .005-.015 .005-.015 .003-.008	.005-.030 .010-.020 .005-.010 .005-.015 .010-.022 .005-.010
Steel
100 Brinell 200 Brinell 300 Brinell	125 - 175 70 - 90 40 - 50	450 - 600 350 - 450 200 - 250	.004-.010 .004-.010 .003-.005	.005-.020 .005-.010 .005-.010
Stainless Steel
Hard Others	35 - 70 70 - 105	250 - 400 250 - 400	.003-.005 .003-.005	.003-.012 .003-.012
Titanium
Under 100,000 PSI 100,000 to 135,000 PSI 1,350 PSI & Over	35 - 55 25 - 35 15 - 25	150 - 180 120 - 150 80 - 120	.003-.005 .002-.005 .001-.005	.004-.008 .003-.008 .002-.008
High Temperature Alloys
Ferritic Low Alloys Austenitic Alloys Nickel Base Alloys Cobalt Base Alloys	40 - 60 20 - 30 5 - 20 5 - 10	150 - 300 100 - 235 50 - 150 50 - 100	.002-.005 .001-.004 .001-.003 .001-.003	.003-.008 .002-.006 .002-.006 .002-.006
High Temperature Alloys
180,000 - 220,000 PSI 220,000 - 260,000 PSI 260,000 - 300,000 PSI	25 - 40 10 - 25 6 - 10	120 - 150 80 - 120 50 - 100	.002-.005 .001-.005 .001-.003	.003-.008 .002-.008 .002-.006

The selction of initial feed within each range will vary with the type of operation. The following is an example of the starting feed for HSS Cutters in mild steel.

Type of Cut	Starting Feed per Tooth
Face Milling Straddle Milling Channel or Slot Milling Slab Milling Sawing	.008 .008 .008 .007 .002