What is it?

The angle grinder is a versatile cutting, grinding, polishing and sanding machine. It is traditionally used for cutting stone and metal, but has a multitude of other uses.

Typical applications include cutting bricks, paving slabs, and roof tiles. Cutting slots and chases in walls. Fast cutting through metal bar, sheet, angle etc, and fast grinding and fettling.

Types

An angle grinder is a good example of a tool that does a few jobs very well! Although there are wide range of makes and models to choose from, angle grinders basically come in two forms: 115mm and 230mm. The smaller tool is lightweight and easy to use single-handed for some applications. The larger machine however, can be quite a handful and should always be used with two hands. The main limitation of the smaller size is limited depth of cut.

Safety

While not as obviously dangerous as say a circular saw, angle grinders still spin the cutting disc very quickly (typically over 11,000 rpm on the smaller machines) and the outside edge of the disc will be doing over 80 m/sec, that's nearly 180mph! Allowing a disc to touch any part of your body can result in a serious burn or cut.

In addition to ear defenders, gloves and eye protection are essential. Eye protection goggles should be of the "indirect" vented design. The more common direct vented type (recognisable by the multiple small open perforations at the side of the goggle) have a habit of letting through small hot shards of metal thrown up by angle grinders. Removing these once they have melted their way into the surface of your eye is not nice!

If you're using an angle grinder for sanding then respiratory protection is also essential since angle grinders have no in-built dust collection facility. When using an angle grinder to drive a wire brush, a leather apron is also to be recommended since picking small wire fragments of out of your stomach or groin is not generally considered to be a pleasant experience!

Take care when cutting or grinding metal, since the grinder will produce copious amounts of sparks. These not only hurt when directed against your person, but are also very able to start a fire should they fall on something flammable.

A word about dust

To say that an angle grinder used to cut masonry produces “dust” is really a mastery of understatement! When used outside you can quickly find yourself operating inside your own local fog. Not only that but you will be finding dust on yours and the neighbours' cars for weeks to come. If you wish to use an angle grinder inside for wall chasing, it is best to do so in a house that is unoccupied! Since by the time you have cut a three or four foot long chase in plaster, there is a good probability you will not even be able to see your hands in front of your face. Note that because of the dust problem a specialist wall chaser, or an SDS drill fitted with a chisel or a chasing gouge is actually a far more appropriate tool in most circumstances.

Discs

Most work with angle grinders is done with cutting or grinding discs. The type of disc dictates the type of work you can do. For metal cutting or grinding the discs are usually made from a reinforced abrasive material. For stone and masonry cutting, you can either use abrasive cutting discs, or alternatively a diamond cutting disc. Whilst significantly more expensive, the diamond disc is almost always preferred to ordinary abrasive discs since it makes a much cleaner and faster cut, and will out last many hundreds of abrasive discs (using several abrasive discs to cut one paving slab is not uncomon), so ultimately it represents much better value. Note that using a diamond disc to cut metal will quickly destroy the disc.

Other accessories

In addition to cutting and grinding discs, an angle grinder is also able to use a number of other types of accessory. These include flap discs for fast and aggressive sanding, wire brushes for rapid rust removal or paint stripping, and mortar rakes for brick removal and repointing activities. Mounting a flat backing pad will also enable the tool to be used for a sanding and polishing.

Quality indicators

The difference in quality between the high end and budget tools it's not as obvious with angle grinders as it is with some classes of power tool, since quality of finish is not usually an issue. Better quality tools will deliver more power to the cutting disc, and less vibration to the operator. On budget tools, the motors will not be rated for continuous operation, and switchgear may be of a lower quality. Better quality tools tend to have bearings and switch gear which are better sealed against ingress of dust. This is especially important when cutting masonry since the dust produced is highly abrasive and can also clog switches.

Accessories

Most angle grinders come with relatively few accessories. Typically you will get a spanner for enabling you to change the disc, and a side handle which can usually be fixed it to the body of the grinder in two or three places to help hold the machine steady.

If you find yourself changing discs frequently, you may find it simpler to buy a quick release locking nut. These replace the usual disc locking nut that requires a spanner to undo, with one that can be simply undone by pulling and twisting on a small lever it is a part of the nut. For prolonged use an anti-vibration handle may also be worthwhile.

Features

On the larger size of tool, slow start is a highly desirable feature, since it prevents the massive kick at switch-on. A removable disc guard can be useful since it will allow a wider range of accessories to be fitted to the tool.

Cordless angle grinders

Cordless angle grinders have appeared on the market recently. These offer the freedom from a power lead, however that freedom comes at a price. Not only are the machines far more expensive to purchase, but you also have a very limited run time since these machines make very heavy demands on their batteries.

Second hand tools

Nothing special to look for, other than making sure that the switch operates correctly, and the lead is undamaged. Pay particular attention to machines that have been used for heavily for cutting masonry. On poor quality tools the dust can result in a sticking power switch which can be very dangerous, as it can lead to a machine you are unable to turn off!