EngineerBenchChoosing milling speeds and feeds
Spindle speed depends on the cutter diameter and the cutting speed suited to the material and tool. Feed rate then depends on RPM, the number of cutting edges, and feed per tooth. Changing diameter without changing RPM changes the cutting speed at the edge; changing flute count without adjusting feed changes the chip load.
Start with the cutter manufacturer's data
Use the material setting as a starting estimate, or enter a supplier's cutting speed and chip load. Enter the diameter at the cutting edge, not the shank. Check the machine's RPM limit. Radial chip thinning applies to the engagement geometry represented by the tool; it is not a reason to increase feed for every cut.
Check the feed you can actually run
Use the reverse calculation to find chip load from an existing feed and RPM. Tool overhang, workholding, coolant, and machine rigidity still affect a usable setting. The calculated feed is not a prediction that the machine can deliver the required cutting force or power.
Following RPM through to table feed
A 10 mm cutter at a selected cutting speed of 100 m/min needs about 3,183 RPM before a machine limit is applied. With four flutes and a chip load of 0.05 mm per tooth, feed is about 637 mm/min. If the spindle cannot reach that speed, calculate feed from the achievable RPM so the intended chip load is preserved rather than using an unrelated feed figure.
The chip-load value is a tooth-by-tooth advance, not feed per revolution. Multiplying by flute count converts between those concepts. Radial and axial engagement affect the cutting condition and must match the supplier data being used. A light radial cut can need a chip-thinning adjustment, but that correction should not be confused with permission to exceed machine or tool limits. Use the reverse mode to check an existing program: divide feed by RPM and flute count to recover the programmed feed per tooth. Compare that value with the actual cutter and operation before changing the program.
Formula
RPM = 1000Vc/(πD). Feed = RPM × feed/rev; milling multiplies chip load by flute count.