A: The idea of "best" depends on what quality factors you are interested in. I have provided some information below, but if you have further concerns, let me know.
Twist drill bit
The twist drill bit, invented by Steven A. Morse of East Bridgewater, Mass., in 1861, is the common drill bit produced in large quantities today. It drills holes in metal, plastic, and wood. The sharpening of the cutting edges is crucial to the performance of the bit. In fact, many people will throw away small bits that become dull, as the bits are inexpensive and proper sharpening is difficult.
The most common bit has a point angle of 118 degrees. A more aggressive angle, such as 90 degrees, is suited for very soft plastics. A shallower angle, such as 150 degrees, is suited for drilling steel. A slight change in angle can result in an inappropriate cutting speed with premature dulling.
For faster removal of the cut wood, the angle of the spiral is increased.
Often, this bit requires a starter hole to avoid wandering, especially at the start.
Brad point bit
The conventional twist drill bit tends to move slightly when it first hits the flat workpiece. We could use a small hole or a hole punch to accurately locate the drill bit. But a better solution for wood and softer plastic is the brad point drill bit (also called a doweling bit or lip and spur bit). The center of this bit is a sharp point that contacts the surface first and will position the bit accurately as the bit is lowered into the wood. In addition, this bit has the outside of the cutting edge that cuts the outer circumference of the hole first before the inside is cut. This will in most cases cut the surface of the hole more smoothly or more cleanly than a conventional bit that tends to tear out the fibers. This cleanly cut surface will be better to glue a dowel to with most adhesives; that is, with a rough surface, the large occasional gaps between the wood piece and the dowel will be too large for most conventional wood adhesives to bridge and maintain high strength.
This bit is also very effective in not causing the entrance of the hole to enlarge if the drill itself moves, vibrates or wobbles. This is because the cutting part of the bit is inside the hole, compared to the conventional twist bit that can cut along its lengt.
Spade bits, also called paddle bits, are used for fast, rough boring in wood. The bit itself is flat with a centering point and with two cutters on the blade. To ensure a smooth hole, sometimes a small spur is put on the outer edge, as in the brad point bit. The spur bit also tends to cause splintering when it cuts entirely through and emerges on the backside of the piece. These bits are used often with electric hand drills.
Forstner bits, named after their inventor Benjamin Forstner, bore precise, flat-bottomed holes in wood, in any grain direction. They are useful for drilling through veneer already glued down. They require substantial force to push them into the material, so would be used in a drill press or lathes rather than in portable drills.
Forstner bits have radial cutting edges to plane off the material at the bottom of the hole. There may also be cutting edges on the sides of the bit to develop exceptionally smooth sides to the hole. Forstner bits have no mechanism to clear chips from the hole, and therefore must be pulled out periodically.
A step bit, step drill, speed bit, or Unibit is a roughly conical bit with a stairstep profile. Due to their design, a single bit can be used for drilling a wide range of hole sizes.
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