A painter needs to know brushes. A chef needs to know knives. And contractors need to know their tools – and every component of them – inside and out.
This quick primer will help any builder get to know their drill bits.
Point Angles
The two most common drill bit point angles are 118 degrees and 135 degrees. The difference between the two is the shape; a 118-degree bit is steeper, more pointed and has a smaller chisel.
The 118-degree bit cuts more aggressively and is generally used for drilling into soft material like wood. Although it can puncture through steel, if used for this, the steeper cutting angle also will cause it to dull more quickly.
A 135-degree bit typically is used for drilling into harder materials, because the pitch makes it easier to drill repeated holes into tougher material.
Splitting the Point
The shaft of a drill bit has two curving grooves – called flutes – that pull debris from the hole being drilled.
In a standard point, the tip is smooth and comes to a slight point. However, unless the wood being drilled provides a solid amount of friction and the drill is perfectly perpendicular to the surface, the smooth standard point can slip off the target and gouge the wood – an issue called “walking.”
The shaft of a good split-point bit features three grooves that lift away debris, allowing the user to drill holes faster and with lower likelihood of snags. These grooves continue all the way to the tip of the bit, where they cut into the tip’s cap, breaking the smoothness and creating a grooved bit tip.
Splitting the point creates a self-centering bit that more easily anchors itself in the wood and keeps a bit on target, helping to eliminate walking and allowing the drill to cut with less pressure. For builders working with hardwoods or other valuable woods, split-point bits help protect the investment in the wood, ensuring better results.
Bit Materials
There are four main types of drill bit materials:
• High-speed steel bits, generally used to drill wood, aluminum and cold-rolled steel.
• Cobalt bits, for tough, high-tensile metals. These are usually split-point and have a higher heat resistance than steel.
• Masonry bits. Used for concrete, mortar, brick and stone, these are mild steel with a carbide tip. Carbide bits are used to drill harder alloys – because of carbide’s dense structure, users can push the drill bits harder than they can with steel bits.
• Tin-coated bits are surface treated for higher heat resistance, low friction and high surface hardness.
Why Sharpen?
Keeping drills bits sharp is critical for getting the job done right – and being able to sharpen them from anywhere is key. Bits can go dull during the course of the workday, and being able to sharpen them right at the jobsite keeps things moving and ensures fast, precise holes.
It's possible to sharpen drill bits by hand, but it takes a considerable amount of time, and requires excellent near vision. Instead, it’s recommended that users sharpen drill bits on a tool specifically designed for the job. These tools use a chuck to hold the bit at a correct, consistent angle, and an abrasive wheel or disc to sharpen the edge. Specialty sharpening tools can be found at large retailers and most local hardware stores.
The same tool can be used to sharpen high-speed, cobalt, and tin-coated drill bit types, but carbide tips require a sharpener with a diamond wheel.
New Home Builder Tips
For home builders, a high-speed steel drill with either a 118-degree or 135-degree drill point will get the job done well.
All-purpose drill bits are best for building applications, unless you need really deep holes, in which case you would use parabolic drill bits.
Forstner bits are often the go-to wood-drilling bit. These bits are guided by the wide outside rim of the bit, unlike most drill bits, which are guided by the tip. Because of that, they can be used along with a drill press to drill angled holes, holes that partially overlap, and holes on the edge of the material.
