Surface feet per minute

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Surface feet per minute (SFM or SFPM) is a unit of velocity used in machining to identify the machinability ratings of a material.

SFM is the velocity around the tool or the material measured in feet-per-minute as the spindle of a lathe turns. The faster the spindle turns, the higher the SFM. The goal is to tool a job to run the SFM as high as possible to increase hourly part production. When SFM is known for a specific material (ex 303 Stainless Steel = 120 SFM for High Speed Steel (HSS) Tooling), a formula can be used to determine spindle speed for live tools or spindle speeds for turning materials.

[edit] Calculation

  • Spindle Speed = SFM / .262 / Stock diameter
  • SFM = Stock diameter(inches) * .262 * rpm (revolutions per minute)


Example: To find the Spindle Speed for a .625 Stainless Steel bar stock using HSS Tooling.

120 SFM / .262 / .625 Dia = 732 Spindle Speed

(.262 is an approximation of π * 1/12).

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