Drill bit buying guide
A drill bit is a tool that can be placed in a suitable chuck of a drilling machine and by means of a pulsating and/ or rotational movement may make round holes in various materials such as wood, metal, stone, concrete, or glass. Confusingly, a drill bit and a drilling machine are both often called "drill". For the clarity of this article we will refer to drill bits and use de term drill for the actual drilling machine.
A variety of drills are suitable for drilling, not every drill is suitable for drilling in every material. Below you find a overview of the types of drills that are suitable for drilling and for which kind of material they are suitable.
- Drill/ Driver (wood, metal and soft stone)
- Hammer Drill (wood, metal, soft stone, hard rock)
- Rotary Hammer (wood, metal, soft stone, hard rock, concrete)
Drill bit types
Just like you can’t use all types of drills for drilling, you can’t use every type of drill bit to drill in every kind of material. Every type of material requires its own specific type of drill bit, also the type of hole you are going to drill weighs in on the decision on which drill bit to use. Below you find an overview of the most common used drill bits and the specific material they can be used on.
Twist bits, also known as high-speed steel bits (HTS), are the most common used drill bits. These drill bits can be used for a variety of materials, knowing wood, plastic, metal and even soft stone materials. That being said the twist is the bit of choice when drilling in metal. There are different types of twist bits available on the market, some are better to use in metal and others on wood.
There are especially a large number of metal drill bits available for the twist bit type. Good twist bits for drilling in hard metals are titanium nitride coated or made of solid cobalt alloyed. Keep in mind when drilling many holes into a specific material it is always better to use a specialized drill bit.
Brad point bits
The brad point bit is the preferred choice for drilling holes in wood. A brad point bit has a lot resemblance with a twist bit, with the exception of a sharp point at the end. This allows you to focus more accurately on the point where you would like to drill the hole, and you have more stability at the start of drilling which prevents outliers.
The auger bit most obvious characteristic is the screw thread shape. At the front of the drill bit is a point to make a start, just like a brad point drill bit. Once pulled into the wood the screw thread works itself deeper into wood. As a result, the borehole is very precisely centered from the point where the drilling is started. It is best to drill at a low RPM so the drill can find its own way into the wood. This type of drill bit is especially useful when drilling deep holes into harder wood types.
A spade bit is the right choice if a relatively large hole must be drilled, but a hole saw is not the solution. A spade bit is designed to drill into wood or wood type materials and cannot be used for metal or concrete surfaces. With a spade bit it is of great importance to drill in a straight line. If you find it hard to drill in a straight line or have to drill in a difficult angle it can be helpful to first drill a pilot hole with a smaller brad point bit.
A countersink may be used to remove a piece of wood to a certain depth and, in a certain width. There are two types of countersink bits, a standalone bit and a drill bit extension. The first one can be used to only drill the notch in which the screw will sink, the later drills a hole and makes the notch at the same time. When you have to drill both the hole and de notch to absorb the screw this is a efficient way of working. The countersink extension bit can be attached to twist and brad point bits. The countersink bits can be used on wood and metal surfaces.
The masonry bit is the standard choice for most types of stone. The drill is recognizable by its top where a sort of “wings” sits. In contrast to a twist or brad point bit the masonry bit does not have a very sharp top. It is advisable to start drilling at a low speed and increase power as the bits grip is increasing. When drilling width holes it is recommended to first drill a pilot hole with a smaller masonry bit. For harder surfaces, you can use a hammer drill. When using a hammer drill it best to drill the first view inches in normal drilling mode. Most hammer drills and masonry bits use a so-called SDS chuck system.
Not entirely by chance is a concrete drill suitable for drilling in concrete. The difference with a standard masonry bit lies particularly in the head of the bit. Concrete drill bits are often of higher quality, and should only be used with a hammer drill. The concrete is cut away instead of planed; this makes it that a high hardness of the head is required. These bits are only suitable for hammer and rotary drill types and make use of the SDS chuck system.
For very hard stone materials a diamond drill can be used. Where metals may not be strong enough for materials such as for example granite, diamond comes through it. It is better not to use diamond bits while drilling in hammer mode, because the friction of the diamond drill head on the hard surface that needs to be drilled is the benefit of diamond drilling.
Forstner bits are useful when drilling shallow holes in wood with flat bottoms. The drill is not meant to drill all the way through the wooden surface. This type of drill is most used for furniture building to install the hinges and fittings to connect two surfaces.
A step bit is to drill holes stepwise in thin plastic and metal. The idea is that the deeper you drill the bigger the hole gets without switching from a small to larger drill bit size.
Spear point bits
Spear point bits are only suitable for drilling into glass and tile surfaces. The bits are recognizable in that there is no thread in these drills. Drilling in glass is must be carried out very carefully to prevent a shoot out or the material breaking. In order to reduce vibration of the glass and to increase the stability it is therefore recommended to place the glass on a wooden board where you can drill through. Because the drilling in glass could be very hot it is wise to stop drilling regularly and cool the drilling surface with liquid.
Drill bit accessories
Every drill is equipped with a chuck; the chuck is the part that holds the drill in place. For one specific type of chuck, the keyed chuck, a chuck key is needed in order to be able to install en switch between drill bits. A chuck key helps you firmly clamp the drill bit inside the chuck. This type is chuck is mainly seen on heavier types of drills, like drills with a hammer function.
Drill depth stop
Sometimes you have to drill onto a particular depth instead of all the way through the service. In these situations it can be helpful to us a drill depth stop. A drill depth stop needs be attached to the drill bit at the same height as the hole that needs to be drilled, measured from the top of the drill bit. When the drill depth stop touches the service you know you have drilled the right depth. Besides a drill depth stop there are also other methods to make sure you drill the right depth.