The cold chisel is a hand cutting tool used by fitters for chipping and cutting off operations.
Chipping is an operation of removing excess metal with the help of a chisel and hammer. Chipped surfaces being rough, they should be finished by filing.
Chisels are made from high carbon steel or chrome-vanadium
steel. The cross-section of chisels is usually hexagonal or octagonal. The cutting edge is hardened and tempered.
Parts of a chisel
- Point or Cutting Edge
Types of Chisels
- Flat chisel
- Cross-cut chisel
- Half-round nose chisel
- Diamond point chisel
- Web chisel
1. Flat chisel
Flat chisels are used to remove metal from large flat surfaces and chip-off excess metal of welded joints and castings.
2. Cross-cut chisel
Cross cut chisels are used for cutting key-ways, grooves and slots.
3. Half-round nose chisel
Half round nose chisels are used for cutting curved grooves (oil grooves).
4. Diamond point chisel
Diamond point chisels are used for squaring materials at the corners, joints.
Web chisels are used for separating metals after chain drilling.
Specification of Chisel
- Width of cutting edge
- Cross section of the body
- Point Angle or Cutting Angle
- Rake Angle
- Clearance Angle
1. Point Angle
The correct point/cutting angle of a chisel depends on the material to be chipped. Sharp angles are given for soft materials and wide angles for hard materials. The correct point and angle of inclination generate the correct rake and clearance angles.
2. Rake Angle
Rake angle is the angle between the top face of the cutting point and normal (90°) to the work surface at the cutting edge.
3. Clearance Angle
Clearance angle is the angle between the bottom face of the point and the tangent to the work surface originating at the cutting edge.
If the clearance angle is too low or zero, the rake angle increases. The cutting edge cannot penetrate into the work. The chisel will slip.
If the clearance angle is too great, the rake angle reduces. The cutting edge digs in and the cut will become deeper and deeper.