Cutting Speed Calculator
Calculate cutting speed, spindle RPM, and feed rate for machining operations.
Calculator
No signup required. Results are indicative—verify for your standards.
Spindle speed: 955 RPM
Formula
RPM = (1000 × Vc) / (π × D), where Vc is cutting speed in m/min and D is cutter/workpiece diameter in mm. Feed rate (mm/min) = RPM × feed per tooth × number of teeth.
Example calculation
Milling 50 mm cutter in aluminium, Vc = 200 m/min: RPM = (1000 × 200) / (π × 50) ≈ 1273 RPM. 4-flute cutter, 0.05 mm/tooth feed: feed rate = 1273 × 0.05 × 4 ≈ 255 mm/min.
Engineering notes
Cutting speed depends on tool material and workpiece material. HSS in mild steel: 20–30 m/min. Carbide in mild steel: 100–200 m/min. Carbide in aluminium: 200–500 m/min. Always verify with tool manufacturer recommendations.
When to use this calculator
- CNC programming — set correct spindle speed and feed rate before running a CNC part program
- Tool life optimisation — find the right cutting speed to balance productivity and tool wear
- Manual machining — set lathe or milling machine RPM from workpiece diameter and material
- New material trials — calculate starting parameters when machining an unfamiliar alloy
- Cycle time estimation — compute machining time from feed rate and cutting path length
Frequently asked questions
- What cutting speed should I use for different materials?
- Typical surface cutting speeds (carbide tooling): mild steel 100–200 m/min, stainless steel 60–120 m/min, cast iron 80–150 m/min, aluminium 200–600 m/min, brass 100–300 m/min, titanium 30–60 m/min. Always start at the lower end and increase if tool life and surface finish are acceptable.
- What is the difference between cutting speed and feed rate?
- Cutting speed (Vc) is the speed at which the tool edge moves relative to the workpiece surface — always in m/min or ft/min. It determines heat generation and tool wear. Feed rate is how fast the tool advances into the material (mm/min or mm/rev). Feed controls chip thickness and surface finish. Both must be set correctly for productive, safe machining.
- Why does RPM decrease when I use a larger diameter cutter?
- RPM = (1000 × Vc) / (π × D). For a fixed cutting speed, RPM is inversely proportional to diameter. A 100 mm cutter rotates at half the RPM of a 50 mm cutter at the same surface speed. This is correct — the larger tool tip travels the same distance per revolution at the correct speed.