Feed Rate Calculator

Why chip load, not just a feed number

Chip load is the actual thickness of material each tooth bites off on a single pass, and it's the number that determines chip formation, tool wear, and surface finish — feed rate (IPM) is just chip load scaled up by how many teeth pass by per minute. Programming a feed rate directly without knowing the chip load it implies is how a change in RPM or a tool swap to a different flute count quietly turns a good chip load into a bad one, even though the IPM number on the screen didn't change.

Picking a chip load to start from

Every tool manufacturer publishes a recommended chip load range for their inserts or end mills by material and tool diameter — that data sheet is a better starting point than a generic rule of thumb, since flute geometry and coating vary a lot between manufacturers. As a rough starting point for a general-purpose 2–4 flute carbide end mill in steel, 0.001–0.003 in per tooth for smaller diameters (under 3/8 in) and 0.003–0.006 in for larger diameters is a reasonable range to dial in from.

Not every flute is cutting on every pass

This calculator assumes every flute engages the material on every revolution, which holds for a full-width slot but not for light finishing passes with a small radial engagement, where not every tooth may be fully loaded depending on cutter geometry and stepover. For light finishing passes, many machinists still use the full chip load calculation as a starting IPM, then adjust by ear and by chip appearance rather than by a second formula.