Types of Drilling tools -LearnMech
Different types of drills are properly used for various applications depending upon work material, tool material, depth and diameter of the holes.
General purpose drills may be classified as:
According to material:
- High speed steel – most common.
- Cemented carbides.
- Without or with coating.
- In the form of brazed, clamped or solid.
According to size:
- Large twist drills of diameter around 40 mm.
- Micro drills of diameter 25 μm to 500 μm.
- Medium range diameter ranges between 3 mm to 25 mm (most widely used).
According to number of flutes:
- Two fluted – most common.
- Single flute – e.g., gun drill (robust).
- Three or four flutes – called slot drill.
According to helix angle of the flutes:
- Usual: 200 to 350 – most common.
- Large helix: 450 to 600 – suitable for deep holes and softer work materials.
- Small helix: for harder / stronger materials.
- Zero helix: spade drills for high production drilling micro-drilling and hard work materials.
According to length to diameter ratio:
- Deep hole drill; e.g. crank shaft drill, gun drill etc.
- General type: L/φ ≅ 6 to 10.
- Small length: e.g. centre drill.
According to shank:
- Straight shank – small size drill being held in drill chuck.
- Taper shank – medium to large size drills being fitted into the spindle nose directly or through taper sockets and sleeves.
According to specific applications:
- Centre drill [Fig. 3.126 (a)] for small axial holes with 600 taper ends to hold the lathe centre.
- Step drill and sub land drill [Fig. 3.126 (b and c)] for small holes with 2 or 3 steps.
- Ejector drill for high speed drilling of large diameter holes.
- Taper drill for batch production.
- Trepanning tool [Fig. 3.126 (g)] for large holes in soft materials.
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