Drill Bit Guide for DIY’ers
From routing wires to drilling pilot holes for fasteners, drill bits are indispensable tools for the professional tradesman as well as the DIY homeowner. In this article, EHT explores a wide range of drill bits to cover the basic types and their various applications.
TWIST BITS AND
COMMON MATERIALS The standard twist-type drill bit is the most mass-produced drill bit on the market. The geometry and sharpness of the cutting edges determine the performance of the bit. The most common twist bit
has a point angle of 118 degrees, which is suited for all sorts of general-purpose tasks. Sharper points, such as a 90-degree angle, provide more aggressive cutting power for materials such as soft plastics. A shallower tip angle, such as 150 degrees, is designed for applications such as drilling steel (but requires a starter hole). The general rule is that harder materials require a large point angle, and softer materials require a sharper angle. Today’s twist bits are available in several material types. Soft, low-carbon steel bits are inexpen- sive, but are only used in wood and require frequent sharpening or replacement. High-carbon steel bits are somewhat more durable and can be used in metal or wood, but excessive heat can damage the cutting edge. For better quality and a step up in hardness, high- speed steel bits (HSS) are more tolerant of heat and can drill through softwoods, hardwoods and metal. Additional materials are now being used to ramp up the per- formance of today’s metal-drilling bits. Cobalt bits are designed for drilling the toughest materials, like hardened stainless steel, cast iron and titanium. These bits combine HSS with a percentage of cobalt, Photo © Bosch