Chip thickness is one of the more important factors affecting tool life. Because feed per tooth affects chip thickness, the highest possible feed per tooth will usually give longer cutter life, but excessive feeds may overload the cutter teeth and cause breakage or chipping of the cutting edges. Optimum feed per tooth can only be determined at the machine as experience is gained on the job. Recommended values from manufactures are specified to provide a secure starting point.

Chip thickness is also affected by the selected milling process. We suggest to use climb milling with the recommended starting feed per tooth. Climb milling creates a chip which immediately has the full thickness, which - while cutting will constantly become thinner until the mill gets out of the material.

For optimum thread quality and tool life, the feed should also incorporate a circular entry & exit curve. This method gives the cutter an even start into the cut and a smooth exit. This even start helps reduce excessive deflection, chatter, and improve size and finish.

Feed Rate - Circular Interpolation

When milling in a circular path, the outside diameter of the cutter is feeding at rate different than that of the cutter centerline. Therefore, it is necessary to determine the machine control calculates the feed rate. Proper calculation of the feed rate is imperative. The following formulas can be used for feed calculations on internal threads.

Feed Rate Measured on Outside Diameter of Cutter

Feed per Tooth x Number of flutes x RPM = Edge Feed ( inch/min )

Feed Rate Measured on Centerline of Cutter

Edge Feed x	( Thread Major Diameter - Cutter Diameter )
	Thread Major Diameter