A cutting speed calculator for turning, drilling and milling
This cutting speed calculator converts a cutting speed into spindle RPM, works out the feed rate and estimates the machining time for a lathe, a drilling machine or a milling machine. It also runs the other way, from RPM back to cutting speed, and it works in metric units (m/min, mm) or inch units (surface feet per minute, SFM, and inches).
Choose a material and it fills in a starting cutting speed and feed from a public-domain source: the US Army training circular TC 9-524, Fundamentals of Machine Tools (1996). Those figures are deliberately conservative starting points for high-speed steel tools, with the manual’s own factors for carbide. Your insert or cutter maker’s recommendations, the rigidity of the machine and the coolant you use can justify very different settings, so every value stays editable.
How to use the Cutting Speed, Feed & RPM Calculator
- Pick Turning, Drilling or Milling, and Metric or Inch / SFM.
- Choose the material, tool type and — for turning and milling — roughing or finishing. The cutting speed and feed fill in from TC 9-524.
- Enter the workpiece, drill or cutter diameter. For milling, enter the number of teeth.
- Add the length of cut or hole depth to estimate the time per pass.
- Read the RPM, feed rate and time. To check a machine setting, switch Find to “Cutting speed from RPM”.
Cutting Speed, Feed & RPM Calculator features
Metric and SFM
n = 1000·Vc ÷ πD in metric, n = 12·Vc ÷ πD (≈ 3.82·SFM ÷ D) in inches.
Three operations
Turning feed per revolution, drilling feed by drill size and milling chip load per tooth.
Starting values by material
Speeds and feeds from TC 9-524 Tables 4-2, 4-4, 7-2, 7-3, 8-1 and 8-3, with carbide factors.
Range check
Shows whether your speed is below, within or above the manual’s range.
Machining time
Time per pass from the length of cut and the feed rate.
The cutting speed formula
Cutting speed Vc is the speed of the work surface past the cutting edge. One revolution moves the surface π × D, so Vc = π × D × n ÷ 1000 with D in millimetres and Vc in m/min, and turned around, n = 1000 × Vc ÷ (π × D). In inch units, with Vc in feet per minute and D in inches, n = 12 × Vc ÷ (π × D) = 3.82 × Vc ÷ D. TC 9-524 rounds the constants to 4 and 320, which gives slightly higher speeds.
Feed rate for turning and drilling is the feed per revolution times the RPM (F = f × n). For milling it is the chip load per tooth times the number of teeth times the RPM (F = fz × z × n). Cutting time is the length of cut divided by F.
Example: a ½ in drill in aluminium at 200 SFM runs at 12 × 200 ÷ (π × 0.5) = 1,528 rpm; the manual’s shortcut 200 × 4 ÷ 0.5 gives 1,600 rpm. At TC 9-524’s feed of 0.008 in/rev the drill advances 12.2 in/min.
Cutting speed for aluminium, steel and other materials
For HSS straight turning, TC 9-524 Table 7-2 gives 200–300 ft/min (61–91 m/min) for aluminium and its alloys, 80–100 ft/min (24–30 m/min) for low-carbon steel, 60–80 ft/min for medium-carbon steel, 40–50 ft/min for stainless steel and 50–80 ft/min for cast iron, and notes that carbide-tipped tools can run 2 to 3 times faster. Table 8-1 lists 400–1,000 ft/min for milling aluminium with HSS cutters and adds 100% for carbide. The table under the calculator shows the full list for the operation you pick.
- Start at the low end of the range, especially on a light machine or a long, slender part, and increase while watching chips, finish and tool wear.
- Modern coated carbide inserts often run far faster than these figures; follow the insert maker’s chart for those.
- Too high a speed burns the edge; too low a feed rubs, work-hardens stainless steel and causes chatter.
Related calculators
Work out gear and pulley ratios with the gear ratio calculator, cutting forces and torques with the torque calculator, and check the hardness of a part with the hardness conversion calculator.
Cutting Speed, Feed & RPM Calculator FAQ
What is the cutting speed formula?
Vc = π × D × n ÷ 1000, with Vc in m/min, D in mm and n in rpm. In inch units Vc (ft/min) = π × D (in) × n ÷ 12.
How do I convert cutting speed to RPM?
RPM = 1000 × Vc ÷ (π × D) in metric, or 3.82 × SFM ÷ D in inches. 24.4 m/min on a 50 mm bar is 155 rpm; the cutting speed calculator does it for any diameter.
What is the cutting speed for aluminium?
With HSS tools TC 9-524 gives 200–300 ft/min (61–91 m/min) for turning and drilling, and 400–1,000 ft/min for milling. Carbide tooling can run faster; check the tool maker’s figures.
How do I calculate milling feed rate?
Feed rate = chip load per tooth × number of teeth × RPM. A 4-flute end mill at 382 rpm with 0.001 in per tooth feeds 1.53 in/min.
What is SFM?
Surface feet per minute, the inch unit of cutting speed. 100 SFM is 30.48 m/min.
Why are these speeds lower than my tool catalogue?
They are 1990s training-manual figures for high-speed steel. Treat them as safe starting points; coated carbide and modern machines usually allow more.