Speeds and Feeds

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

T= Number of teeth in cutter                       f= Feed per tooth in inches
D= Cutter diameter in inches                     W= Width of cut
RPM= Revolutions per minute                    d= Depth of cut
SFM= Surface feet per minute                   HP= Motor horsepower
F= Feed in inches per minute                    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.

Aluminum, Magnesium, Dural - 4.0 plus
Brass - 2.5
Soft Bronze, Copper - 2.0
Cast Iron - 1.5
Steel up to 150 Brinell, Malleable Iron - 0.75
Steel, 300 Brinell, Hard Bronze - 0.6
Steel, 400 Brinell - 0.5