Industrial Drilling Processes and Tool Mechanics

The Drilling Process

Drilling is a metal removal operation which aims to make circular holes in a part's section. It is performed with specialized tools called bits. These operations range from manual machines to large-scale industrial equipment.

Essential Tools for Drilling

The drill bit is the primary tool for creating cylindrical, conical, and other types of holes. This tool is typically made from a cylindrical steel rod featuring helical slots (flutes) that facilitate chip removal. The tip of the bit contains cutting edges formed at the intersection of these slots.

The surface behind the cutting edge is beveled to ensure that only the edge makes contact with the material. The cylindrical margins of the slots form beveled edges that act as a guide. The width of this strip depends specifically on the diameter of the drill.

Technical Specifications and Angles

• The tip angle: 118º for steel and up to 130º for light metals.
• Tilt angle (Helix angle): 15º for steel and brass, 30º for cast metal, and 40º for light metals.
• Shank (Mango): The part that is attached to the drilling machine. It often features slots and maintains a cylindrical shape.

Specialized Drill Bit Varieties

Multi-flute bits: These usually have 3 or 4 slots and are used to enlarge or finish existing holes.

Counterbore/Step drills: These act as a guide for a previously drilled hole.

Countersink bits: These have a conical shape and are used as deburring tools to produce a conical housing.

Oil-hole drills: These feature internal holes to deliver lubricant directly to the cutting area, which helps to lighten the load and reduce friction.

Drill Movement and Metal Removal

For the metal removal process to occur, the drill must be subject to two distinct motions:

• Rotation: The bit rotates around its own axis; this is the main cutting motion. Rotation speed is usually indicated on the machine in revolutions per minute (RPM).
• Translational motion (Feed): The penetration movement of the drill. The bit progresses by finding new material to cut with its blade. Progress is usually measured in mm/rev.

Calculation Formula: n = (V_c × 1000) / (π × d)

Professional Sharpening Techniques

During use, the tip undergoes rounding (wear). You must sharpen it before it deteriorates due to overheating. Proper sharpening must achieve:

• The appropriate tip angle for the material.
• Leading edges that have exactly the same length.
• A correct point geometry to ensure a sharp tip.