What is cutting tools?
Cutting tools perform the main machining operation. They comprise of single point cutting tool or multipoint cutting tools. It is a body having teeth or cutting edges on it.
A single point cutting tool (such as a lathe, shaper and planner and boring tool) has only one cutting edge, whereas a multi-point cutting tool (such as milling cutter, milling cutter, drill, reamer and broach) has a number of teeth or cutting edges on its periphery.
Single Point Cutting Tools
There are mainly two types of single point tools, namely the solid type as shown in the figure and the tipped tool also shown in the figure.
Fig. Solid type of single point cutting tool
The solid type single point tool may be made from high speed steel, from a cast alloy.
Fig. Tipped type single point cutting tool
Brazed tools are generally known as tool bits and are used in tool holders.
Fig. Index-able insert type single point cutting tool
The tipped type of tool is made from a good shank steel on which is mounted a tip of cutting tool material. The tip may be made of high speed steel or cemented carbide. In addition to this, there are long index-able insert tools and throw away.
The Insert type tool throws away refers to the cutting tool insert which is mechanically held in the tool holder. The inserts are purchased which are ready for use. When all cutting edges are used, the insert is discarded and not re-sharpened.
These tools can be further classified depending upon the operations for which they are used and the type of the shank (straight or bent shank type). Tools may be of the types planning tools, turning tools, facing tool, boring tools, parting and slotting tools etc.
Different types of carbide tips are generally used on tipped tool. In general the straight shank type tools are cheaper to manufacture as compared to bent shank type.
But bent shank type can be used for turning either longitudinal or cross feed without resetting and for turning, facing and chamfering operations. Boring tools usually quite long and the cross-section is small.
A single point cutting tool can be understood by its geometry shown in the figure. Geometry comprises mainly of nose, rake face of the tool, flank, heel and shank etc. The nose is shaped as conical with different angles.
The angles are specified in a perfect sequence as American Society of Tool Manufacturer for recognizing them as under.
Nomenclature Single Point Tool
The elements of tool signature or nomenclature single point tool is illustrated in figure.
Fig. Elements of tool signature or nomenclature of single point tool
(i) Back rake angle
It is the angle between the face of the tool and a line parallel with base of the tool measured in a perpendicular plane through the side cutting edge.
If the slope face is downward toward the nose, it is the negative back rake angle and if it is upward toward the nose, it is positive back rake angle. This angle helps in removing the chips away from the work piece.
(ii) Side rake angle
It is the angle by which the face of tool is inclined side ways. This angle of tool determines the thickness of the tool behind the cutting edge.
It is provided on tool to provide clearance between work piece and tool so as to prevent the rubbing of work- piece with end flake of tool.
It is the angle between the surface the flank immediately below the point and the line down from the point perpendicular to the base.
(iii) End relief angle
It is the angle that allows the tool to cut without rubbing on the work- piece. It is defined as the angle between the portion of the end flank immediately below the cutting edge and a line perpendicular to the base of the tool, measured at right angles to the flank.
Some time extra end clearance is also provided on the tool that is also known as end clearance angle. It is the secondary angle directly below the end relief angle
(iv) Side relief angle
It is the angle that prevents the interference as the tool enters the material. It is the angle between the portion of the side flank immediately below the side edge and a line perpendicular to the base of the tool measured at right angles to the side.
It is incorporated on the tool to provide relief between its flank and the work piece surface. Some time extra side clearance is also provided on the tool that is also known as side clearance angle. It is the secondary angle directly below the side relief angle.
(v) End cutting edge angle
It is the angle between the end cutting edge and a line perpendicular to the shank of the tool. It provides clearance between tool cutting edge and work piece.
(vi) Side cutting edge angle
It is the angle between straight cutting edge on the side of tool and the side of the shank. It is also known as lead angle. It is responsible for turning the chip away from the finished surface.
(vii) Nose radius
It is the nose point connecting the side cutting edge and end cutting edge. It possesses small radius which is responsible for generating surface finish on the work-piece.
Convenient way to specify tool angles by use of a standardized abbreviated system is known as tool signature or tool nomenclature.
It indicates the angles that a tool utilizes during the cut. It specifies the active angles of the tool normal to the cutting edge. This will always be true as long as the tool shank is mounted at right angles to the workpiece axis.
The seven elements that comprise the signature of a single point cutting tool can be stated in the following order:
Tool signature 0-7-6-8-15-16-0.8
1. Back rake angle (0°)
2. Side rake angle (7°)
3. End relief angle (6°)
4. Side relief angle (8°)
5. End cutting edge angle (15°)
6. Side cutting edge angle (16°)
7. Nose radius (0.8 mm)