If cutting speed of a drill bit is 19.8 m/min, find the rpm of spindle if diameter of drill is 10.5 mm.

Concept:

Cutting speed:

• Cutting speed is the speed at which the cutting edge passes over the material while cutting, and is expressed in meters per minute.
• It is given by:

V = \(\frac{\pi~\times~D~\times~N}{1000}\) m/min

Where, D = Diameter of drill (mm), N = rpm, V = Cutting speed in m/min

• For a particular diameter drill if spindle speed of machine is increased, the cutting speed increases.
• Cutting speed is also sometimes stated as surface speed or peripheral speed.
• The selection of the recommended cutting speed for drilling or turning etc. depends on the materials to be machined, and the tool material.

Calculation:

Given:

cutting speed of a drill bit, V = 19.8 m/min

diameter of drill, D = 10.5 mm

∵ \(V = \frac{\pi~\times~D~\times~N}{1000}\)

⇒ 19.8 = \(\frac{\pi~\times~10.5~\times~N}{1000}\)

⇒ N = 600 rpm