Difference between orthogonal and oblique cutting

This article is about orthogonal cutting and oblique cutting.

Basically, the metal cutting process can be classified into two main types.

  • Orthogonal cutting
  • Oblique cutting

In this article, we are going to see these two cutting process types along with their differences.

Orthogonal cutting and oblique cutting diagram
Orthogonal cutting & Oblique cutting

What is Orthogonal cutting?

The orthogonal cutting process is a two-dimensional cutting analysis in which the tool’s cutting edge is perpendicular to the direction of cutting speed. The chip is formed due to shear deformation in the shear plane. This shear deformation is a result when the force is applied to the cutting tool. 

Orthogonal cutting diagram
Orthogonal cutting

The angle between the shear plane and the workpiece is known as the shear angle. The sharp cutting edge of the tool separates the chip from the workpiece while the cutting tool was subjected to some forced conditions. The region where the chip sticks to the cutting surface of the tool is known as the sticking region.

The analysis of orthogonal cutting is simpler than oblique cutting because only two forces (Tangential force and feed force) are involved. During chip formation, some sort of energy will be consumed. The cutting is uniform along the cutting edge of the tool.

In the orthogonal cutting process, there are three deformation zones in cutting.

  • Primary shear zone
  • Secondary deformation zone
  • Tertiary zone

In the primary shear zone, the cutting edge of the tool was penetrated into the workpiece and shearing of the work material occurs. In the secondary deformation zone, the sheared work material undergoes gradual deformation and moves along the cutting tool surface. The newly machined surface where the tool rubs are known as the tertiary zone. It is also called a friction zone.

What is oblique cutting?

The cutting edge of the tool is perpendicular to the cutting velocity in the orthogonal cutting whereas, in oblique cutting the cutting edge of the tool is inclined at a certain angle to the cutting velocity vector. It is also called a three-dimensional cutting process. 

Oblique cutting diagram
Oblique cutting diagram

Oblique cutting involves three forces (Tangential force, Feed force, and Radial force) and it makes complex to analyze when compared to orthogonal cutting.

In oblique cutting, the chip formation is always helical in the manner and does not slide over the cutting surface of the tool. The cutting velocity has an inclination angle in the cutting operations. This helical chip moves sideways and away from the cutting zone. 

In oblique cutting the chip can become thinner and longer if the rake angle and the inclination angle increases. Also, the cutting force will be decreased.

Difference between orthogonal and oblique cutting process

The difference between orthogonal cutting and oblique cutting is given below.

Orthogonal cuttingOblique cutting
The inclination of the cutting edge of the tool is perpendicular to the cutting tool velocity or cutting speed.In oblique cutting, it is inclined at an acute angle with the normal to the cutting velocity vector (direction of the tool travel).
The chip flows over the surface of the cutting tool in orthogonal cutting and the chip movement is normal to the cutting edge.The chip flows on the surface of the cutting tool at an angle (chip flow angle) with normal to the cutting edge.
In orthogonal cutting, the chip coils in a tight flat spiral.In oblique cutting, the chip flows sideways in a long curl.
The cutting edge of the tool clears the width of the workpiece.In orthogonal cutting, it may or may not clear the width of the workpiece.
The thickness of the chip may be slightly increased in the middle.Whereas in oblique cutting, it may not occur.
In orthogonal cutting, only two force components (Tangential force and feed force) acts on the cutting tool.Whereas in oblique cutting, there are three force components (such as Tangential force, Feed force, and Radial force) acting on the cutting tool, and they are mutually perpendicular to each other.
Tool contacts the chip only on the rake face in orthogonal cutting.At sometimes, multiple cutting edges may be in contact to chip in oblique cutting.
In orthogonal cutting, tool life will be less.Tool life will be more while comparing orthogonal cutting.
It is easy to analyze.It is complex to analyze.
The surface finish is not as good as oblique cutting.Better surface finishes while comparing orthogonal cutting.