1- Twist Drill - Design and Fabrication

The twist drill name came about due to the original manufacturing process of the drill not just the the appearance. The manufacturing process was to rough mill the flutes in a straight line along the body then heat it up and twist it into the now familiar spiral shape. The twisted shaft was then semi-finished milled, heat treated and then ground to size.

Although the twist drill is simple to use the drill is not simple a great deal of work has been performed in making it a precision tool. After the drill has been ground to size the tip is formed. The most common tip angle for a drill is 118 degrees. Over the years the 118 degree lip has proven to work well on most materials however to be more efficient other degrees are recommended for certain types of materials. This is particularly true if a large amount of drilling is going to occur on one part or large, quantities runs on material that is hard or soft. Blunt angles, (130-150 degrees) for harder material, and more acute angles (60-90 degrees) for gummy softer materials.

The twist drill are manufactured as right and left handed, (the right hand is prevalent), and composed of three principal parts;

  1. The Shank (solid part of the drill that does not have flutes), straight or tapered.
  2. The Point or Tip (does the cutting).
  3. The Body (flutes and cutting end).