Three Numbers, One Concept

• fz — feed per tooth: how far the workpiece advances during the engagement of a single cutting edge. This is the chip load — the actual bite each tooth takes — and it's the number tool manufacturers publish as a starting recommendation, because it's tied directly to chip thickness and tool life regardless of spindle speed or tool diameter.
• fn — feed per revolution: fz multiplied by the number of teeth (fn = fz × z) — how far the workpiece advances in one full spindle revolution, combining every tooth's bite.
• Vf — table feed: the number that actually gets programmed into the CNC controller, in mm/min or in/min. It's the linear speed of the table relative to the workpiece.

The Formula

Vf = fz × z × n, where z is the number of flutes on the cutter and n is spindle speed in RPM (equivalently, Vf = fn × n). This is the calculation every CAM system and control ultimately runs to turn a chip-load recommendation into an actual program feed rate.

Why Feed Per Tooth Is the Number That Matters

Manufacturers publish chip-load charts in fz, not Vf, because fz is independent of spindle speed and tool diameter — it describes the physical bite the edge has to survive, which governs edge wear, chip evacuation, and cutting force. Change the RPM or swap to a cutter with more flutes, and Vf has to change to keep fz constant. Feeding by a fixed Vf regardless of RPM or flute count is a common way to accidentally overload — or badly underload — the cutting edge.