Enter surface feet per minute, tool diameter in inches, feed per tooth in inches and the number of cutting flutes. Obtain the cutting conditions from the tooling manufacturer for the actual material, tool and engagement. The unit conversion is 12/π, so the displayed spindle speed uses the unrounded factor rather than the shortcut 3.82.
Recommended values vary by material, coating, tool and machine rigidity, and the numbers here are starting points. Deep cuts and long tool stick-out reduce the feasible feed. Small machines cannot reach high RPM.
Chip thinning at light radial engagement calls for adjusted feeds. Safety guards and eye protection are essential.
Spindle speed (RPM) from surface speed (SFM)
| Surface speed (SFM) | 100 |
|---|---|
| Tool diameter | 0.5 |
| Chip load | 0.002 |
| Number of flutes | 2 |
| Spindle speed (RPM) | 763.9 |
| Feed rate (in/min) | 3.1 |
Common error: Running the same RPM for every cutter. The speed depends on the diameter, and a smaller tool must spin faster to reach the same surface speed.
Feeds and Speeds: formula
ASME B1.1: Unified Inch Screw Threads · Sandvik Coromant: Milling formulas
Feeds and Speeds: changing Surface speed (SFM)
| Surface speed (SFM) | Spindle speed (RPM) | Feed rate (in/min) |
|---|---|---|
| 80 | 611.2 | 2.4 |
| 90 | 687.5 | 2.8 |
| 100 (example) | 763.9 | 3.1 |
| 110 | 840.3 | 3.4 |
| 120 | 916.7 | 3.7 |
Feeds and Speeds: compare input ranges
| Input | Tested from | To | Spindle speed (RPM): low input | Spindle speed (RPM): high input | Swing |
|---|---|---|---|---|---|
| Tool diameter | 0.45 | 0.55 | 848.8 | 694.5 | 154.3 (20%) |
| Surface speed (SFM) | 90 | 110 | 687.5 | 840.3 | 152.8 (20%) |
| Chip load | 0.0018 | 0.0022 | 763.9 | 763.9 | 0 |
| Number of flutes | 1 | 3 | 763.9 | 763.9 | 0 |
Feeds and Speeds: individual input comparisons
| Input | Value | Spindle speed (RPM) | Feed rate (in/min) |
|---|---|---|---|
| Surface speed (SFM) | 80 | 611.2 | 2.4 |
| 90 | 687.5 | 2.8 | |
| 100 | 763.9 | 3.1 | |
| 110 | 840.3 | 3.4 | |
| 120 | 916.7 | 3.7 | |
| Tool diameter | 0.4 | 954.9 | 3.8 |
| 0.45 | 848.8 | 3.4 | |
| 0.5 | 763.9 | 3.1 | |
| 0.55 | 694.5 | 2.8 | |
| 0.6 | 636.6 | 2.5 | |
| Chip load | 0.0016 | 763.9 | 2.4 |
| 0.0018 | 763.9 | 2.8 | |
| 0.002 | 763.9 | 3.1 | |
| 0.0022 | 763.9 | 3.4 | |
| 0.0024 | 763.9 | 3.7 | |
| Number of flutes | 0 | 763.9 | 0 |
| 1 | 763.9 | 1.5 | |
| 2 | 763.9 | 3.1 | |
| 3 | 763.9 | 4.6 | |
| 4 | 763.9 | 6.1 |
Spindle speed (RPM): Surface speed (SFM) against Tool diameter
| Surface speed (SFM) / Tool diameter | 0.4 | 0.5 | 0.6 |
|---|---|---|---|
| 80 | 763.9 | 611.2 | 509.3 |
| 90 | 859.4 | 687.5 | 573 |
| 100 | 954.9 | 763.9 | 636.6 |
| 110 | 1,050.4 | 840.3 | 700.3 |
| 120 | 1,145.9 | 916.7 | 763.9 |
Feeds and Speeds: values and definitions
| Quantity and definition | Value used |
|---|---|
| Surface speed (SFM) — Recommended surface speed for the material and tool, in surface feet per minute. | 100 |
| Tool diameter — Cutting tool diameter, in inches. | 0.5 |
| Chip load — Feed per tooth, in inches. | 0.002 |
| Number of flutes — Number of cutting flutes on the tool. | 2 |
| Spindle speed (RPM) | 763.9 |
| Feed rate (in/min) | 3.1 |
Tool diameter: half and double
| Tool diameter | Spindle speed (RPM) |
|---|---|
| 0.25 | 1,527.9 |
| 0.5 | 763.9 |
| 1 | 382 |
Feeds and speeds tell a machine how fast to spin and how fast to move so a cutter cuts instead of rubbing. A half inch cutter at 100 surface feet per minute spins at about 764 RPM, and with two flutes and a chip load of 0.002 inch the feed is about 3.1 inches per minute. Too fast wears the tool and too slow rubs and heats the work.
The surface speed and chip load come from the tool maker's chart for the material.
Start from the tool manufacturer's recommendation for the material and adjust by the sound and the chip color. Machine rigidity and depth of cut change what works.
Check surface speed on the surface speed calculator, drill sizes on the tap drill and thread engagement pages and dimensions on the length converter. The torque and power converters relate to machine limits, and the circle area page relates to tool geometry.
What is the feed-per-tooth input?
It is programmed feed per cutting tooth: feed rate divided by spindle revolutions per minute and number of flutes. Actual chip thickness also depends on engagement geometry.
What is surface feet per minute?
Cutting-edge surface speed in feet per minute. Select the recommended value for the material, tool and operation, then convert it to spindle speed using the diameter.
Does this establish an approved machine setup?
No. Check the tooling data and the machine’s speed, feed, power and workholding limits. This arithmetic does not evaluate rigidity, runout, engagement or cutting forces.