Single Point Cutting Tool -Parts, Operations, Advantages and Disadvantages
Single point cutting tool is used in lathe machine, shaper machine and many different machines.
It is used for operations like turning, facing, camfering, boring, shaping etc. Single point cutting tool has only one main cutting edge called Principal cutting edge which arises from the intersection of rake surface and principal flank surface.
It is named single point cutting tool as it has single point for cutting purpose. This tool is used to remove materials from the workpiece.
Single point cutting tool is mainly used for remove metal from workpiece to transform metal into require shape and size.
It removes large amount of metal from workpiece in very less amount of time by rotating the workpiece and making contact of workpiece with this tool.
Parts of Single Point Cutting Tools:
1 Shank:
Shank is the part of tool that is clamped. It is the main body of the tool and is present beside the cutting point. It is held by tool post.
2 Side Rack Angle:
Side Rack Angle is the angle between the face and the plane perpendicular to the side cutting edge.
It is provide in front of clamp. Side Rack Angle is used to pass the chips. The chips go by this side rack angle smoothly when the material cut by side cutting edge.
3 Side Relief Angle:
It is the angle made by the side flank to the plane perpendicular to the base. It provide relief to the tool by preventing the friction of tool due to workpiece and prevent contact of tool with the workpiece.
4 Face:
The top surface of tool over which the chips slides after cutting is known as Face. It is the horizontal surface adjacent of cutting edges.
5. Flank:
Flank is the vertical surface adjacent to the cutting edge. It is also known as cutting face. There are two flank side flank and end flank.
Side flank is also called major flank and lies adjacent to side cutting edge.
End flank is also called minor flank and lies adjacent to end cutting edge.
6 Base:
The bottom surface of the tool is known as base. It is the portion of the flank that lies opposite to the top face of the shank.
7 Nose or Cutting Point:
The intersection point of major cutting edge and minor cutting edge is called Nose.
8 Nose Radius:
The intersection point of major cutting edge and minor cutting edge is called Nose and this nose does not have a sharp profile as it will cause scratches in the workpiece.
9 Cutting Edge :
The edge of the tool which removes the material from the workpiece is called cutting edges.It lies on the face of the tool. Single point cutting tool has two edges and these are:
10 Heel:
It is a curved portion and intersection of the base and the flank of the tool.
Angles of single point cutting tool:
1 Side Cutting Edge Angle:
It is the angle between the side cutting edge and a line parallel to the shank is called Side cutting Edge Angle.
Side cutting edge angle is used to maintain the width of chip. If the side cutting edge angel angle is increased, width of chip increases and as it decrease, width of chip also decreases. It is also used to avoid formation of built up edge and distributing of cutting force.
2 End Cutting Edge Angle:
The angle formed between the end cutting edge and a line perpendicular to the shank is called end cutting edge angle.
It allow only for small question of end section edge to contact the machining surface and also the vibration and chatter are prevented. The angle will be formed 5 degrees to 15 degrees.
3 Lip Angle/Wedge Angle:
It is the angle between the face and end flank or minor flank of the single point cutting tool.
4 Back rack angle:
The angle formed between the tool face and line parallel to the base is back rack angle. It allows the smooth flow of chip. It is provided to increase the life of the tool. Back rack angle is itself of three types- positve rack angle, negative rack angle and zero rack angle.
For ductile materials positive rack angle is used and for brittle materials negative rack angle is used. Brass is machined with zero rack angle.
5 Image of Back Rack Angle and End Relief Angle:
6 End Relief Angle :
The angle formed between the minor flank or end flank and the line normal to base of the tool is called end relief angle.
7 Side rack angle:
The angle between the face of tool and a line perpendicular to the shank is called side rack angle.
Side rack angle is used to maintain width of chip formed after cutting.
Image of Side Rack Angle and Side Relief Angle:
8 Side Relief Angle:
The angle formed between the major flank or side flank and the plane normal to the base of the tool is called side relief angle.
This angle avoids the rubbing between workpiece and flank when the tool is fed longitudinally.
Different Value Of Rake angle and its effect :-
Rake surface is the chip flowing and orientation of this rake surface is indicated by rake angles.
Rake angle is a crucial factor to judge machining action. The value of the rake angle can be positive, negative and zero.
The value of the rake angle determines the value and power requirement, life of the cutting tool, chip deviation, etc.
The value of rake angle generally varies from -15 degrees to +15 degrees. But in some cases, it can reach up to +30 degrees.
Effects of positive,negative and zero rake angle.
Based on the inclination/elevation of rake surface, rake angle can either be positive,negative or zero.
Positive rake angle:
The positive rake angle has sharp cutting edge and also offers less chip deformation during the machining process.
Cutting force required is less in positive rake angle. So, the power requirement during machining is also less.
Positive rake angle is generally used to cut soft materials as rake surface experiences high pressure during positive rake angle machining.
Positive rake angle also helps in achieving better machinability. Machinability is the ease with which a metal can be cut (machined) permitting the removal of the material along with a good finish.
Negative rake angle:
Unlike the positive rake angle, negative rake angle offers a strong tool tip due to which the tool becomes more resilient under impact loading. It also resists plastic deformation at high cutting temperature due to thick cutting edge which can absorb as well as dissipate more heat.
Negative rake angle increases the tool life. But due to large wedge angle, shear deformation of chip increases and thus higher force is required. Negative rake angle provides discontinuous chips, which is bad in terms of machinability.
Negative rake angle is generally used to cut hard materials.
Zero rake angle:
Zero ranke angle is intermittent of positive and negative rake angle.It provide advantage and disadvantages of both to some extent.
Zero rake angle is very easy to design and calculation for estimating machining force is very easy in zero rake angle.
Types of cutting using single point cutting tool:
There are two types of cutting using single point cutting tool :-
1) Orthogonal Cutting.
The cutting operation in which the cutting edge of tool is perpendicular to the cutting velocity is known as Orthogonal Cutting.
In this type of cutting, the chip flow in the direction normal to cutting edge.
2) Oblique Cutting.
The cutting operation in which the cutting edge of tool is not perpendicular to the cutting velocity is known as Oblique Cutting.
In this type of cutting, the chip flow make an angle with normal to cutting edge.
Operations using single point cutting tools:
Single point cutting tool can be used in many operations but turning is the most common operation done using single point cutting tool. Apart from turning, single point cutting tool is also used in :
i) Slotting Tool
ii) Shaping Tool
iii) Planing Tool
iv) Boring Tool
Advantages of single point cutting tool:
1) Design and fabrication of single point cutting tool is simple and very less time consuming.
2) Single point cutting tools are cheaper than its alternative.
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Disadvantages of single point cutting tool:
1) In single point cutting tool, tool wear rate is high as it continuously remains in physical contact with the work material during machining and hence tool life becomes low.
2) Due to continuous contact, rate of increase in temperature is high which increases the tool wear rate and also causes thermal damage to the surface of the workpiece.
3) The material removal rate (MRR) in single point cuttting tool is low as only one cutting edge takes the entire depth of cut.
4) As high temperature is reached while using single point cutting tool, it causes deformation of the tool plastically.
