Drill bits are among the most common and essential accessories used in construction and DIY projects. There are thousands of different types, sizes and applications for drill bits.
Read on to find answers to some of the most frequently asked questions in our comprehensive guide to drill bits.
What are drill bits?
Drill bits are metal cutting tools used with drills to create holes in many different types of materials. The most common types of drill bits are designed with helix flutes and a cutting point, and are powered to cut holes by rotation and torque from a drill.
How are drill bits made?
Drill bits are made from different grades of raw steel which are delivered to manufacturing plants. The steel goes through a process of cutting and heat treatment at extremely high temperatures, to harden the steel. The bits are then cleaned, tempered, grounded, fluted and pointed. Specialist drill bits go through additional processes such as split pointing.
Who invented drill bits?
The concept of a drill bit is thousands of years old, but the modern twist drill bit that we are most familiar with was invented around 160 years ago.
American Steven A. Morse, from Massachusetts, invented the twist drill bit in 1861. Before his invention, drilling was a slow and laborious process because drill bits were made from a pointed, sharp, flat piece of metal which overheated too quickly. He wanted to develop a more effective way to drill a hole and gained a US patent for a twist drill in 1863.
Drill bits and their uses
Drill bits are used to drill small to large holes in stone, granite, marble, concrete, brick, plaster, plastic, steel, wood, composites, ceramic tiles, glass and much more.
It is important to make sure that you use the correct type of drill bit to match the material you are drilling into. When choosing which drill bit to buy or use, consider its material, its strength and cutting power.
Drill bits for metal and plastic
- High-speed steel (HSS) drill bits are designed for drilling through steel, copper, hardened plastic, iron, brass, cast iron and other difficult materials. They are ideal for general use because they are very durable and resistant to heat and abrasion.
- Cone cutting drill bits are used for drilling different sized holes (or expanding pre-cut holes) in non-ferrous sheet metals and plastic.
- Multi-cut stepped drill bits are specialist, conical shaped drill bits used to make multiple hole sizes in thin material without having to constantly adjust the bit size. They are most useful for thin sheets of material, and to enlarge existing holes.
Drill bits for wood
- Auger drill bits can drill shallow and deep holes in wood. The point and large flutes work to create a neat hole and remove wood debris while cutting.
- Flat drill bits have two cutting spurs and a center point which allows for precision when cutting holes in different types of wood such as hard wood, soft wood, plywood, chipboards and MDF.
- Holesaw and arbor drill bits are used with holesaws to cut into nail-embedded wood, plywood, as well as metal, plastics, pipe and stainless steel.
- Pilot and spade, lip and spur (brad point) drill bits are optimal for drilling holes in wood. The sharp brad point and spurs ensure clean, precise and fast drilling. They are often referred to as brad point or dowelling bits.
Drill bits for masonry and concrete
- SDS drill bits (Special Direct System) are robust tools used with a power drill in hammer mode. This helps achieve more power when drilling masonry, brick, concrete and other similar materials.
- Tungsten carbide drill bits are manufactured from high grade steel with zinc plating, and are coated with tungsten carbide on the tip to increase durability. This is necessary as masonry bits heat up rapidly.
Cobalt drill bits vs. titanium vs. black oxide
Both cobalt and titanium drill bits are used to make holes in hard, tough materials like metal. Cobalt drill bits are the toughest you can get, and have no coating, unlike titanium drill bits.
Titanium bits are coated with titanium nitride or carbonitride to reduce the effects of heat.
These drill bits are not as robust as cobalt drill bits and you cannot sharpen them without the risk of removing some of the coating.
Black oxide is the most basic coating used on drill bits to provide resistance to heat, lubrication and slow down oxidation to the metal. It helps extend the life of particular drill bits, but it doesn’t provide any additional strength.
What size drill bits do I need?
The diameter and flute length of the drill bit you need will depend on the hole you need to drill.
Drill bit diameter
Here are some simple guidelines for the diameter:
- For soft wood: Use a bit 1/64” (0.4mm) smaller than the required hole size
- For other materials: Use a bit the same size as the hole required.
Drill bit flute length
In terms of length, use a drill bit which is as long as the screw or object to be inserted. For example, a 40mm screw would need a drill bit that has a flute length of at least 40mm.
The flute length is the distance from the point of the bit, to the neck.
For more specific guidance on what size of drill bit to use, refer to pilot hole charts for the particular bits and material you’re using.
How to use and maintain drill bits: Our top tips
- Choose the right size of drill bit for the job - a drill bit that is too long has a higher risk of breaking
- Drill a pilot hole in the material you’re drilling for more accuracy, especially in wood
- Make sure the drill bit is set properly straight in the chuck of your drill. Always use downward or forward pressure in a straight line when drilling
- Use a tight grip and apply firm pressure to the drill; enough so the drill bit bites into the material, but not too much that the bit slides
- Use the right speed setting for the surface you’re drilling. Hard materials need a lower speed, while soft surfaces need faster speeds
- Masonry drills need to be kept as cool as possible when you’re using them because they get extremely hot. Keep a jug of cold water nearby to cool them down
- Clean your drill bits often when you’re using them - this will maintain their optimal performance as it helps to stop them from overheating
- Keep your drill bits clean, free of debris and store them in a dry place to prevent rust
- To sharpen drill bits, you can use a bench grinder. Watch the video below to see how.
Why do my drill bits keep breaking?
There are several reasons which could explain why your drill bits keep breaking:
- It could be the wrong type for the material to be drilled;
- It could have overheated;
- The drill speed could be too high;
- You’re applying too much side loading on the bit (not drilling perpendicular);
- The drill bit could be set incorrectly in the chuck;
- The drill bit could be poor quality.
How much are drill bits?
Drill bits are very good value for money. General purpose drill bits are the lowest price. For example, a pack of 10 HSS Roll Forged Drill Bits starts from £1.16 (inc VAT). Specialist drill bits such as multi-cut stepped bits can be more expensive. Generally, the longer and wider the drill bit, the more expensive it will be.