Holesaw choice and tips on use.
There are 2 main types of holesaw used in DIY, plus a couple of related items.
As pictured above, DIY holesaws are usually a cylinder shaped barrel with saw teeth on the open end. A central pilot drill bit is fitted. These usually come in sets with sizes optimised for electricians or plumbers.
These can drill to almost the depth of the holesaw. For very thick materials, if the saw is withdrawn and the cut centre of the wood chopped out, it can then drill the same depth again.
Holesaws come in carbon steel, bimetal and HSS. The better ones are HSS, and these will drill wood, metal or plastic. The others will drill wood and plastic.
With Starrett cutters and all systems which are compatible (e.g. Bosch and Sandvik), the arbor and the cutter are separate, and there are two sizes or arbor and two types of pilot drill.
Interchangeable blade holesaw
These are very poor performers, though just about workable with care. They also don't last long, expect half a dozen holes per blade size if you're consistently careful. Often they wont last that long.
The sawblades are weak and have little support, and very gentle pressure must be used at all times. A momentary application of moderate force and they break, damaging the workpiece. They also don't tolerate fast rotational speed, since the sawblade is poorly supported.
These need to be withdrawn to clear debris regularly during use. They can only drill to the depth of the blade protrusion, so thicker items like doors will need to be drilled from both sides to make the hole. Stop just short of full depth penetration, or the metal casting will scrape the workpiece.
These have an abrasive cutting edge rather than saw teeth, and are used on masonry. Most used in DIY are designed to work dry, but there are also ones that need a flow of water to cool and clear debris.
Due to the hard nature of masonry, a snag is likely to cause injury, and core drills should be used with a drill that has a safety clutch.
Holesaws may use carbide or diamond abrasive. Diamond is used on tiles.
Hammer action is not usually used with a diamond core drill or an abrasive tile drill. There are core drills available that are designed to be used with hammer action, but many are not suitable for this, and usually it isn't needed.
Some drill bits are also used for large holes. These include
- Flat bit - tend to produce a messy edge to the hole.
- adjustable flat bit - adjustable hole width
- Auger - very neat, but drilling angle not correctable during work. Can also be used in a hand brace or impact driver.
- MAD bit - wander readily, can correct misaligned holes
- Cone bit - these make large holes in thin sheet material, mainly plastic & metal. Available in continuous and stepped size types. Tidy the hole up by drilling from the other side a little too.
For more detailed info on these drill bits, see Drill bit
piccy These comprise a rotating arm with one or two moveable cutting blades.
Typically designed for large holes (commonly around 30mm to 150mm) in thin soft materials, primarily plasterboard. Limited depth of cut (around 20-30mm) so more often useful for sheet materials, eg: cutting downlighter holes in a plasterboard ceiling.
A router can be used to make very large holes in sheet material.
Punches can be used with sheet metals and non-brittle plastics.
- In use the drill needs to be kept straight, or the hole will be misshapen
- Keep pressure fairly gentle, or the saw will snag
- The final hole size often doesn't match the holesaw size. If size matters, test first on some scrap wood
- If the pilot drill is blunt, pre-drill a centre hole with another drill bit
- To enlarge an existing hole, just fill the hole first. Jam a piece of round timber into it, or attach a bit of sheet wood under the old hole
- Holesaws are for use on wood, plastic, and in many cases metal. They're not for masonry
- Core drills are for masonry only
- When cutting thin or flexible material, clamp some wood to the back of it
- If you need to cut out a disc with no centre hole, cut a disc from some scrap the usual way, fix it onto the material you wish to drill, then holesaw over it without the pilot bit protruding into the interior of the holesaw. This way the first disc controls the holesaw position instead of the pilot bit.
The main safety issue with holesaws is the tendency to snag. When this happens, the drill is yanked round forcefully, potentially causing a wrist injury. Its best to use a drill with a safety clutch, this is designed to slip in such situations, minimising the likelihood of injury. Nearly all cordless drills have this feature.
Where a holesaw is used in a drill with no safety clutch, take care not to let hands wander over to one side during drilling, and keep drilling speed and force low. Less than careful use with no safety clutch can soon lead to hospital.