Metal cutting theory: Basic objectives of efficient and Economical machining practice, Basic elements of machining, Orthogonal And Oblique Cutting, Classification of Cutting Tools

Metal cutting theory

1. Economical manufacture of Machine parts is a big challenge Growing competition.

2. Basic objectives of efficient and Economical machining practice.

a) Quick metal removal.
b) High class of surface finish.
c) Economy in tool cost.
d) Less power consumption.
e) Economy in the cost of replacement and sharpening tools.
f) Minimum idle time of machining tools.

3. Basic elements of machining.

a) Work piece 
b) Tool and 
c) Chip.
Metal cutting theory


The relative motion between the tool and work piece is necessary for effecting the cutting action. The relative motion can be provided by both keeping the work piece stationary and moving the tool or by keeping the tool stationary and moving the work or by moving both in relation to one another.
The work piece provides the parent metal, from which unwanted metal is removed by cutting action of tool to obtain shape and size of the component. Chemical composition and physical properties of work piece material will have significant effect in machining.
The type and geometry of chip formed are greatly affected by the metal of work piece, geometry of cutting tool and method of cutting. Chemical composition and rate of flow of cutting fluid have considerable influence over the machining operation.

Orthogonal And Oblique Cutting:

The process of metal cutting is divided in to two main classes: 
1. Orthogonal cutting and 
2. Oblique cutting. 

Orthogonal cutting

In Orthogonal cutting, cutting edge of tool remains normal to the direction of tool feed or work feed.
The direction of chip flow velocity is normal to the cutting edge of the tool.

The angle of inclination ‘i’ of the cutting edge of the tool with normal to the velocity vc is zero.

The chip flow angle i.e the angle between the direction of chip flow and normal to the cutting edge of the tool is zero. Cutting edge is longer than the width of the cut.

Oblique cutting:

The cutting edge of the tool always remains inclined at an acute angle to the direction of tool feed or work feed.

The direction of chip flow velocity is at an angle
with normal to the cutting edge of the tool. The angle is known as chip flow angle.

The cutting edge of the tool is inclined at an angle ‘i’ with the normal to the direction of tool feed or work feed.

Three mutually perpendicular components of the cutting forces act at the cutting edge of the tool.The cutting edge may or may not be longer than the width of cut.

Most of the metal cutting is carried out through oblique method.

Classification of Cutting Tools

Single point tools: 

Those having only one cutting edge. Ex. Lathe tools, Shaper tools, Planer tools, Boring tools etc.

Multi-Pont tools:

Those having more than one cutting edgeEx. Milling cutters, Drills, Broachers, Grinding wheels.

Cutting Tools Can Also Be Classified According To The Motion As:

Linear motion tools: 

Lathe, Boring, Broaching, Planning and Shaping tools.

Rotary motion tools: 

Milling cutters, grinding wheels.

Linear And Rotary Tools: 

Drills, Honing Tools, Boring Heads Etc.


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