Cutting Speed

What is Cutting Speed (VC)?

Cutting speed is generally defined as the relative velocity between the surface of the workpiece and the cutting tool. Some experts also define it as how fast the workpiece moves past the cutting edge of the tool. Machinists measure it in meters per minute (m/min) or feet per minute (ft/min). The cutting speed is a quite important factor in the determination of other parameters of CNC machining, such as cutting temperature, power consumption, tool life, etc. Its influence in these parameters serves as a significant difference between feed rate and cutting speed.

It is necessary to ensure that the cutting speed is optimum so that the CNC machining process will give the best part. However, it is possible to predict the optimum cutting speed for a particular CNC machining process by considering other factors. Examples of such factors include:

  1. Workpiece Hardness

One of the most important factors that determine cutting speed is the hardness of the material being cut. The harder the material, the slower the cutting speed, and vice versa. For example, machining materials like steel will require a lower cutting speed compared to aluminum.

As a rule, the harder the workpiece material, the slower the cutting speed you should implement during machining. For example, materials like titanium will require a lower cutting speed compared to steel.

  1. Cutting Tool Material

There are different lathe tools (parting, turning, threading etc.) used for various CNC machining. Each of these tools is also made with different materials, hence possessing different hardness properties. The cutting tool material will have a significant impact on the cutting speed used in a machining process. If the cutting material is of high strength, the machinist can utilize a high cutting speed to a little detriment. However, softer cutting tool materials will tend to wear out quickly with higher cutting speeds. This will lead to shorter tool life.

  1. The Expected Tool Life

How long the machinist wants the tool to last is another factor that is important in determining the cutting speed. This will include considering variables such as how much the tool cost and the cost of the tool compared to the quantity of parts being produced. If variables like this are favorable, then a high speed might be feasible for use.

Other factors might include depth of cut, tool geometry, type of machine tool, surface quality requirements.

Cutting Speed Calculations: 

Cutting Speed is the speed at which the metal is removed by the cutting tool from the workpiece. In the case of lathe machine cutting speed is the peripheral speed of the work past the cutting tool. It is expressed in length/time.


Where D = diameter of the workpiece

N = rpm of the work

In Imperial (US) units:

  • Vc [SMF] – Cutting Speed
  • n [RPM] – Spindle Speed
  • D [Inches] – Workpiece diameter in Turning and Cutter Diameter in Milling
Metric Units:
  • Vc [mm/min] – Cutting Speed
  • n [RPM] – Spindle Speed
  • D [mm] – Workpiece diameter in Turning and Cutter Diameter in Milling