Cromwell stock a wide range of hole making tools designed for all drilling applications. With well-known brands like Dormer and Kennedy, you'll be sure to find the right tooling solution for your individual needs and application.

What is drilling?

Drilling is cutting application that utilises a drill bit to cut a circular hole in hard materials. The tool works by rotating and is pressed against the surface of allowing its cutting edges to cut through the material creating chips. Drills are available in many types and sizes with metric and imperial measurements available.

When are drills used?

Drills of some description are used in the majority of hole making applications. On e of the most common types of drill is the twist drill which features 2 or more flutes arranged in a twist allowing chips to be evacuated efficiently. They are commonplace in drilling machines and versions of them are used with handheld power tools for everyday domestic use.

Depending on the type of cutting application more specialised drill can be used. For example, drilling sheet metal requires the use of a step drill which is named because of its conical tip that resembles the steps of a pyramid. These types of drills allow precise hole making of varying diameters.

When drilling hardened metals, then carbide drills can be employed. These types of drills are made from a tungsten carbide compound instead of the standard steel alloy or high-speed steel and feature a harder, sharper cutting edge. Their drawback is that they are more expensive and less resistant to breakage through knocks and being dropped and as such are usually reserved for specialist usage.

Types of drills

There are a wide variety of drills and hole making tools, suitable for different industries, applications, and levels of experience. To help with the tool selection process Cromwell has outlined a selection of the most common types.

Twist drill - The most common type of drilling tool, the twist drill comes with a multitude of variations of its own. General purpose twist drills are known as jobber drills and are used in a wide range of applications from woodwork to metalworking. Longer length versions of twist drills are available for specialised applications, sometimes known as aircraft drills. Twist drills are commonly made from high-speed steel or a cobalt compound for tougher materials. Many feature coatings such as oxidised and titanium nitrate for greater durability and lasting sharpness. There are also carbide versions of twist drills designed for tackling hardened metals.

Centre drill - Centre drills are double-sided drills with a 60-degree, stepped point. Usually operated in a lathe with either a drill chuck or collet chuck. They commonly come in two types, although there is a third type that is not as commonly used. They are:
Type A - Used in the formation of centre holes with a 60-degree chamfer.

Type B - Forms a hole with 2 chamfers, one measuring 60 degrees and another measuring 120 degrees. The latter helps in protecting the hole against damage that can lead to inaccuracies.

Type R - Forms a centre hole allowing for more holding accuracy due to the contact at a single point. The trade-off is that the holes load bearing capacity is reduced.

Step Drill - Named because of its conical tip that resembles the steps of a pyramid, these types of drills are ideal for drilling sheet metal as their specialised tip allows both variation and accuracy of sizing.

Replaceable head/insert - These drills feature a body tool with either a replaceable head or individual cutting inserts that make up the part of the tool that actually does the cutting. They are widely used in specialist industrial applications. An advantage of this is that the entire drill doesn't need replacing when the cutting edge has become dull, however they tend to be costly items so they are rarely used outside of industrial machining.


What drilling bit do I need?

This is primarily dependant on several factors, what material you are drilling, what size hole you are drilling, what type of hole you are drilling and how many workpieces you are drilling.

The material being drilled will determine what hardness of drill you will need, for example wood and softer metals or materials would probably require high speed steel, but for hardened materials such as tool grade steel then high-speed steel might result in a dulled cutting edge and a reduction in the tool lifespan. Carbide drills are better at retaining their sharpness and are used to cut harder materials such as hardened steel.
Sizing is also a key component, drills are available in a range of diameters and lengths with imperial and metric measurements. Making sure the size of the hole matches the size of the fastener is also paramount.

There are also different types of hole that different drills are designed for. A simple pilot hole can be drilled using a twist drill, however centre drilling applications requires the use of a centre drill as these are designed to be operated on a lathe chuck.

In the case of large scale industrial drilling a replaceable head or insert drill might be more appropriate as these machines are designed for rapid machining applications with little down time.