Machining Surface Speed & Feed Rate Calculator

Direct answer. Enter the diameter being cut and your own target cutting speed (SFM or Vc in m/min) - this tool does not supply or assume that number for you. It solves the spindle RPM that produces that surface speed, then applies the feed convention for the operation you selected.

Method. Surface speed relates diameter and RPM by SFM = (pi x D_in x RPM) / 12, or in metric Vc (m/min) = (pi x D_mm x RPM) / 1000. Solving for RPM gives RPM = (SFM x 12) / (pi x D_in), or RPM = (Vc x 1000) / (pi x D_mm). Because a real spindle is set to a whole RPM, the result also shows the surface speed actually achieved once RPM is rounded.

Turning vs. milling feed - not the same formula. In turning, the tool feeds a fixed linear distance per spindle revolution, so axial feed rate = RPM x feed-per-revolution. In milling, the cutter has multiple teeth engaging per revolution, so table feed rate = RPM x number-of-flutes x feed-per-tooth (chip load). Using a turning feed-per-revolution value as if it were a milling feed-per-tooth value (or vice versa) is a common and costly real-world mistake, so this calculator keeps the two input sets and result labels clearly separate.

Worked example. Turning a 1 in diameter workpiece at a target 350 SFM with a 0.008 in/rev feed: RPM = (350 x 12) / (pi x 1) is about 1,337 RPM, and the axial feed rate is about 10.7 in/min. Milling with a 0.5 in diameter, 4-flute end mill at 350 SFM with a 0.002 in/tooth chip load: RPM is about 2,674 RPM, and the table feed rate is about 21.4 in/min.

Definitions. SFM/Vc is the linear speed of the material passing the cutting edge at the stated diameter, not the spindle's rotational speed. RPM is spindle revolutions per minute. Feed-per-revolution and feed-per-tooth are both linear distances, not speeds, until multiplied by RPM (and, for milling, flute count).

The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.

Operation

Turning (lathe)

Units

Imperial (in, SFM)

Diameter

1

Target cutting speed (SFM / Vc)

350

Feed per revolution (turning only)

0.008

Flutes / teeth (milling only)

4

Feed per tooth / chip load (milling only)

0.002

Primary result: Spindle speed: 1337 RPM.

• Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
• Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
• When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.

User-entered target, not a material prescription. This tool never states or looks up "the correct" surface speed for a material, tool material, coating or coolant combination - those recommendations vary enormously by tooling manufacturer, insert grade, machine rigidity and operation, and only your tooling supplier's data or shop practice can set that number responsibly. Enter your own vetted target.

Results are ideal geometric relationships. They do not account for tool deflection, chip thinning at light radial engagement, ramping/helical moves, climb vs. conventional milling, coolant strategy, machine horsepower or rigidity limits, or interrupted cuts. Verify the computed RPM and feed rate are within your machine's and tool holder's rated limits before running them.