Calculate feed per tooth, feed rate, or spindle speed from table feed, RPM, and effective cutter teeth in metric or imperial milling units.
Feed Per Tooth Formula
The following formula is used to calculate the feed per tooth (fz) for a milling operation:
Variables:
- fz is feed per tooth (mm/tooth or in/tooth)
- vf is table feed rate (mm/min or in/min)
- n is spindle speed (revolutions per minute)
- z is the cutter’s effective cutting teeth per revolution for the feed formula, not the number simultaneously in contact
- Axial depth of cut is not used in this feed-per-tooth relationship
Divide table feed by spindle speed multiplied by effective teeth. For example, 600 mm/min ÷ (5,000 RPM × 4 teeth) = 0.03 mm/tooth. Reverse forms are vf = fz × n × z and n = vf ÷ (fz × z). Use matching length units; 1 inch = 25.4 mm. Feed per tooth is nominal advance per tooth and can differ from maximum chip thickness. Follow the tool maker’s cutting data and setup limits.
What is a Feed Per Tooth?
Feed Per Tooth, often abbreviated as FPT or Ft, is a critical parameter in machining operations, particularly in milling. It refers to the distance that the mill or cutter travels along the workpiece for every single tooth pass. This measurement is typically given in inches or millimeters and is crucial in determining the speed and feed rate of the milling operation. The Feed Per Tooth is directly related to the surface finish of the workpiece, the tool life, and the rate of material removal. Too high a feed per tooth can result in tool breakage or poor surface finish, while too low a feed per tooth can lead to inefficient machining and excessive tool wear. Therefore, it is essential to calculate and set the correct Feed Per Tooth for each specific machining operation.
