How To Choose the Right Holesaw

What Are Holesaws?

The holesaw does what its name implies – it’s a specialist type of drill bit that bores out circular holes in material. A hole saw (also sometimes called a hole cutter) uses a cylindrical or cup-like blade with a serrated lower edge to bore a hole that is significantly wider than that which can be achieved with a conventional drill bit. Typical uses for holesaws include making cutouts in ceilings for downlights or other light fittings, drilling holes for routing cables and electrical wiring, making holes for fitting taps and other plumbing hardware to baths and sinks, installing locks and handles in doors and cutting routes for ventilation ducts and pipes in masonry.

Holesaws can be used to make holes in virtually all common construction materials, including timber, metal, plasterboard, ceramics, glass, bricks and plastics. Different types of design of holesaw exist to suit different materials, although High Speed Steel (HSS) and diamond-tipped holesaws can be used on a wide range of materials.

How do Holesaws Work?

While a drill bit works from its tip outwards, removing the core material as dust, a holesaw works differentially. As its name suggests, it makes a circular cut, leaving a ‘plug’ of material inside the holesaw which is then removed when the cut is complete. The holesaw is only making a single circular cut. This means they are much quicker and more efficient than drill bits when it comes to cutting holes, never mind the numerous cases when the hole required is bigger than any practical drill bit can be.

Many holesaws have the ability to mount an arbor or pilot drill. This is a conventional drill bit that attaches in the centre of the holesaw blade and protrudes through it. This provides a way to initially align the holesaw, and helps locate the holesaw as it cuts through the material, ensuring that the hole is straight and doesn’t drift or turn oval as it is cut. Having an arbor fitted to the holesaw also allows you to work from both sides of the cut (if both are accessible, at least). Drilling all the way through in one direction can lead to a lot of tearing or ripping of the material in the final stages of the cut. But with an arbor, you can cut in one direction until the arbor breaks through, then cut in the other direction, using the arbor to ensure the correct alignment.

How To Choose The Right Holesaw

The two key factors to consider when selecting a holesaw are the diameter and the depth. The diameter of the cutting ring will determine the width of the resulting hole and should be suitable for the final purpose needed. The depth of the holesaw determines how much material you can bore through before the core of the saw becomes full of material (the plug formed as the saw cuts its way down). Once this is full the holesaw will not be able to cut any further. So, the holesaw’s depth should ideally exceed the depth of the hole you’re cutting.

If it doesn’t, then you will have to stop to clear the plug from the core. Many holesaws have slots or gullets in the side of the blade so that a screwdriver can be used to push out the plug of material. Others may even have an ejector spring which will push the plug out when released, and some holesaws can have ejector springs fitted as aftermarket upgrades.

Two other considerations when choosing a holesaw relate to the teeth. Many modern holesaws feature variable pitch teeth, where the angle and shape of the teeth changes in a pattern around the circumference of the saw. This reduces wear and vibration and makes for a faster cut, but the resulting cut can be rougher. Constant pitch teeth tend to wear more quickly and cut at a slower pace but produce finer and more precise cuts with less tearing of the material.

The other measure is teeth per inch – how many teeth are on each inch of the holesaw’s circumference. This is a bit like the ‘gearing’ for the holesaw, as fewer teeth will each take a bigger ‘bite’ of material, while lots of smaller teeth will take a smaller, finer bite. So, a holesaw with a low TPI (under 5 TPI) will cut quickly but with a rougher finish, while higher TPI (10 or more) will cut more slowly but with a smoother result.

When to Use a Metal Holesaw

The most common sort of general purpose holesaw is a ‘bi-metal’ holesaw. These tools usually have cobalt alloy HSS (High Speed Steel) for the cutting teeth and alloy steel bodies. These are close to being a ‘universal’ type of holesaw, suitable for cutting all major construction materials. The added strength and durability of the bi-metal construction means these holesaws are ideal for resistant metals such as mild steel and stainless, but they also work effectively in wood, plastic and plaster.

When To Use a Tungsten Carbide Holesaw

Standard bi-metal holesaws can cut through metals. However, they will wear out quickly, especially if regularly used to cut through thick metal. Holesaws can be optimised for working with metal with tungsten carbide teeth. These have greatly improved hardness and heat dissipation and so perform better and last longer when cutting metal. Therefore, these are the best holesaws for metal but will be unnecessarily expensive for users who only occasionally cut through metal and mostly use holesaws on wood or plastic.

When to Use a Diamond Holesaw

Diamond is the hardest natural material and so makes for an excellent cutting agent. Diamond holesaws have a continuous diamond-coated cutting edge rather than individual teeth. The diamond’s hardness and temperature resistance make a diamond holesaw ideal for use with ceramics, stone, glass, marble, porcelain and other similar materials.

Choosing the Right Holesaw

Hopefully our holesaw guide has demystified these useful tools. From now on, when selecting a holesaw, whether you’re buying one for a specific job or choosing one from a holesaw set, bear the following factors in mind:

1. Use a bi-metal holesaw for most standard construction materials. One with tungsten carbide teeth will perform better and last longer when cutting metal, while one with a diamond cutting edge will be best for ceramics.
2. As well as choosing a holesaw that’s the right diameter for the hole you’re cutting, also choose one that’s deep enough and collects enough material to avoid having to stop the cut to empty the core too often. It’s always best to be able to make the cut in a single action.
3. The design and number of teeth can have a big impact. Fewer teeth are quicker but rougher, while a high number of teeth are slower to work but produce a cleaner cut.

Holesaws at Rennie Tool Company

Rennie Tools offers two lines of holesaw. We supply a range of bi-metal holesaws with and without fittings for arbor drill bits, in sizes ranging from 14mm to 250mm. Rennie Tool also manufacturers a six-piece set of diamond holesaws suitable for use on ceramics and porcelain, with sizes of between 6mm and 16mm, or individual diamond holesaws of between 6mm and 150mm in diameter. For more information or to place an order, visit our website and contact us today.