Cutting Speed, Feed And Depth Of Cut in Machining

Cutting speed of a tool can be defined as the rate at which its cutting edge passes over the surface of the work-piece in unit time. It is normally expressed in terms of surface speed in meters per minute.

In machining it is important as it considerably affects the tool life and efficiency of machining. Selection of proper cutting speed has to be made very judiciously. If it is too high, the tool gets over heated and its cutting edge may fail, needing regrinding. If it is too low, too much time is consumed in machining and full cutting capacities of the tool and machine are not utilized, resulting in lowering of productivity and increasing the production cost.

Feed

Feed of the cutting tool can be defined as the distance it travels along or in to the work-piece for each pass of its point through a perpendicular position in unit time. In turning operation of lathe, it is equal to the advancement of the tool corresponding to each revolution of work. In planning it is the work, which is fed and not the tool. 

In milling work, the feed is considered per tooth of the cutter.

The cutting speed and feed of a cutting tool is largely influenced by the following factors:

1. Material being machined.

2. Material of the cutting tool.

3. Geometry of the cutting tool.

4. Required degree of surface finish.

5. Rigidity of the machine tool being used

6. Type of coolant being used

Depth of cut

It is indicative of the penetration of the cutting edge of the tool in to the work-piece material in each pass, measured perpendicular to the machined surface i.e. it determines the thickness of metal layer removed by the cutting tool in one pass.

Example: In turning operation on a lathe it is given by

Where D = Original diameter of the work-piece in (mm)

d = Diameter obtained after turning in (mm) in one pass.