Types of Drilling tools -LearnMech

Drilling tools

Different types of drills are properly used for various applications depending upon work material, tool material, depth and diameter of the holes.

Read More : Classification/Types Of Drilling Machine use In Mechanical Workshop

General purpose drills may be classified as:

According to material:

1. High speed steel – most common.
2. Cemented carbides.
3. Without or with coating.
4. 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:

1. Usual: 200 to 350 – most common.
2. Large helix: 450 to 600 – suitable for deep holes and softer work materials.
3. Small helix: for harder / stronger materials.
4. 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:

1. Centre drill [Fig. 3.126 (a)] for small axial holes with 600 taper ends to hold the lathe centre.
2. Step drill and sub land drill [Fig. 3.126 (b and c)] for small holes with 2 or 3 steps.
3. Ejector drill for high speed drilling of large diameter holes.
4. Taper drill for batch production.
5. Trepanning tool [Fig. 3.126 (g)] for large holes in soft materials.

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