Cutting speed (Vc) is the speed at which the cutting edge of a tool moves relative to the material being machined. It is typically expressed in surface feet per minute (SFPM) in imperial units or meters per minute (m/min) in metric units. Cutting speed plays a crucial role in machining, as it affects tool life, surface finish, and overall efficiency.

Formula for Cutting Speed
Cutting speed is related to spindle speed and tool diameter through the following formula:

Where:
- Vc = Cutting speed (SFPM or m/min)
- D = Diameter of the tool or workpiece (in inches or mm)
- N = Spindle speed (RPM)
- The constants 12 (for inches to feet) and 1000 (for mm to meters) adjust the units accordingly.
To determine the necessary spindle speed based on a given cutting speed:

Factors Affecting Cutting Speed
- Material Being Machined – Harder materials generally require lower cutting speeds, while softer materials allow for higher speeds.
- Cutting Tool Material – Cutting speed limits vary significantly based on tool material:
- High-Speed Steel (HSS) operates at lower cutting speeds.
- Carbide tools allow for significantly higher speeds than HSS.
- Ceramics and CBN (Cubic Boron Nitride) can run at much higher cutting speeds than carbide, particularly for hard materials.
- Type of Operation – Turning, milling, drilling, and grinding each involve different cutting conditions that influence optimal cutting speeds.
- Coolant & Lubrication – Effective cooling allows for higher cutting speeds by reducing thermal damage and tool wear.