CNC Basics
CNC Chip Load Explained: Formula, Feed Rate and RPM
Published · Updated
Chip load expresses nominal feed per cutting tooth. It links linear feed to spindle revolutions and cutting flutes. The relationship helps check a program or translate a supplied parameter; the equation alone does not select a suitable material or machine setting.
The relationship
Chip load = feed rate ÷ (RPM × flute count). Using mm/min produces mm/tooth; using in/min produces in/tooth. Flute count is the number of cutting edges.
Rearrange for feed: feed rate = chip load × RPM × flutes. For spindle speed: RPM = feed ÷ (chip load × flutes). RPM and flute count are counts, not dimensional measurements.
Worked check, not a recommendation
At 6000 mm/min, 18000 RPM and two flutes, nominal chip load is 6000 ÷ (18000 × 2) = 0.166666… mm/tooth. This is arithmetic, not a recommended woodworking or metal-cutting parameter.
If feed stays fixed and RPM doubles, nominal chip load halves. If RPM stays fixed and feed doubles, chip load doubles. Changing flute count also changes the relationship; a two-flute result cannot be reused unchanged for another cutter.
Consistent imperial and metric inputs
An inch feed must be paired with inch chip load. Mixing 100 in/min with a millimeter chip load produces an incorrect RPM calculation. CutNavi converts physical values together while RPM and flute count remain unchanged.
For example, 0.01 in/tooth equals 0.254 mm/tooth. Unit equivalence does not imply either value is suitable for a particular operation.
What the equation leaves out
Nominal feed per tooth is not a complete model of actual chip thickness. Engagement, tool geometry, material and machine capability affect the operation. Consult tooling manufacturer guidance for the specific setup.
Use Chip Load Calculator to check a supplied feed/RPM combination, Feed Rate Calculator with a specified chip load and RPM, or RPM Calculator when the other inputs are fixed. None produces CAM or machine-specific recommendations.