“Feeds and speeds” are the two settings that govern every cut: how fast the tool spins and how fast it moves through the material. Get them right and you get clean cuts and long tool life; get them wrong and you burn or break tools.
Speed (RPM)
Spindle speed comes from the material’s recommended surface speed (SFM) and the tool diameter:
Feed (IPM)
Feed rate comes from how big a bite each tooth takes (chip load), the number of flutes, and the RPM:
How they relate
Surface speed protects the tool from heat; chip load protects it from rubbing (too light) or overload (too heavy). Change one and you often re-balance the other. Manufacturers publish starting SFM and chip-load values by material and tool diameter — start there, then tune by the sound of the cut, the look of the chips, and the finish.
Frequently asked questions
Difference between feed and speed? Speed is spindle RPM; feed is how fast the tool advances.
What is chip load? The thickness of material each tooth removes per revolution.
Where do I get starting numbers? Tool manufacturer charts, by material and tool diameter.