Select the most appropriate cutting angle of the chisel for chipping Mild steel 

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ISRO VSSC Technician-B (Fitter) Official Paper (Held On: 14 July 2021)
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  1. 70°
  2. 65°
  3. 55°
  4. 45°

Answer (Detailed Solution Below)

Option 3 : 55°
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Detailed Solution

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Explanation:

Angles of chisels:

Point angles:

  • The correct point/cutting angle of the 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.

Material to be cut

Point angle / Cutting angle

Angle of inclination

High Carbon Steel

65°

39.5°

Cast iron

60°

37°

Mild steel

55°

34.5°

Brass

50°

32°

Copper

45°

29.5°

Aluminum

30°

22°

Clearance angle:

  • The 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.

Rake angle:

  • The rake angle is the angle between the top face of the cutting point, and the normal (90°) to the work surface at the cutting edge.

Crowning:

  • A slight curvature is ground called Crowning to the cutting edge of the chisel, to prevent the digging of corners, which leads to breakage of the chisel point.
  • Crowning allows the chisel to move freely along a straight line while chipping.
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