Surface feet per minute


Surface feet per minute is the combination of a physical quantity and an imperial and American customary unit. It is defined as the number of linear feet that a location on a rotating component travels in one minute. Its most common use is in the measurement of cutting speed in machining. It is a unit of velocity that describes how fast the cutting edge of the cutting tool travels. It correlates directly to the machinability of the workpiece material and the hardness of the cutting tool material. It relates to spindle speed via variables such as cutter diameter or workpiece diameter.
SFM is a combination of diameter and the velocity of the material measured in feet-per-minute as the spindle of a milling machine or lathe. 1 SFM equals 0.00508 m/s . The faster the spindle turns, and/or the larger the diameter, the higher the SFM. The goal is to tool a job to run the SFM as high as possible to increase hourly part production. However some materials will run better at specific SFMs. When the SFM is known for a specific material, a formula can be used to determine spindle speed for live tools or spindle speeds for turning materials.
In a milling machine, the tool diameter is used instead of the stock diameter in the following formulas when the tool is revolving and the stock is stationary.
Spindle Speed can be calculated using the following equation:
SFM can be calculated using the following equation: