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A good angle grinder is an indispensable addition to any home toolbox. They are very affordable, and can tackle a whole host of home, garden, and other DIY tasks.
At first glance they're a fairly uncomplicated tool, so making a choice should be easy. Think again – a quick scan of tool catalogs and websites reveals a huge selection.
It's made all the more difficult when some of the differences seem relatively small. Are they important? Will ignoring a particular detail turn out to be an expensive mistake?
In essence, this is a very simple tool. A power source (usually an electric motor) drives a set of gears, which in turn rotate the head. The head is situated at a 90-degree angle to the motor. A wheel is clamped to this head via a threaded retaining ring. There's a safety guard that usually covers the rear half of the disk. This can often be rotated, to change the spark/debris path.
The users grip the main body, with additional control offered by a side handle (mountable on the left or right). A switch or trigger operates the grinder, sending power to rotate the wheel. There's usually a lock button for the trigger, so you don't have to keep your finger on it all the time.
A spindle lock prevents movement when changing wheels.
In auto body shops and metalworking shops, the power source is often compressed air. These businesses have several compressed air tools, so it's a viable solution. That’s not usually the case at home. Tools sold by DIY stores are almost invariably electric, though they may be corded or cordless.
What gives the angle grinder its tremendous versatility is the variety of different wheels and other gadgets you can attach.
An angle grinder can perform an enormous range of jobs:
Removing paint or rust, preparing surfaces for painting (brushing or spraying).
Polishing auto bodywork or other painted surfaces.
Grinding welds to a smooth finish.
Cutting pipe for plumbing, severing bolts, and chopping rebar for reinforcing concrete.
Sharpening lawnmower blades or garden shears.
Tuckpointing walls.
Cutting concrete, stone, and ceramics.
Carving wood.
Two factors determine the capability of your angle grinder:
Wheel size
Motor power
Sizes given for angle grinders indicate the maximum wheel diameter they can take.
There are some very powerful, heavy-duty angle grinders in the 7" to 9" range, but they are beyond what most home users need.
For DIY tasks, a 4 ½" angle grinder is more than enough. It's by far the most common tool available. Some, slightly confusingly, are called 4 ½” 5”, which tells you they'll also take a 5" disk. Though a few of these models are available, it's the 4 ½” wheel size that's important. There's neither benefit nor disadvantage to the multi-size model.
In terms of power, you'll see any combination of horsepower, amps, watts, and rpm.
Horsepower (hp) is usually only shown for larger angle grinders. A top-rated 9" model can generate 5 hp or more, which is a fearsome figure for a hand-held tool. To give you a rough comparison, that's the same as a big gas lawnmower.
Amps is the measure generally used with 4 ½” angle grinders. Technically, amperage tells you the electrical load on the motor, but for our purposes, you can look at it more simply: the more amps, the more power you've got. DIY angle grinders start at about 4 amps, though we suggest 6 amps as a useful minimum. Anything above 10 amps is a very powerful tool – as much as most people will ever need.
Wattage is not often shown. Though different from amps, it can still be considered as a rating of the motor's power output. Again, it's a case of more is better.
RPM is the rotational speed of the wheel. There are notable differences between large and small angle grinders. A 9" model will typically have a maximum rpm of 6,000 to 7,000. A 4 ½” tool will run at 9,000 rpm or more.
Though not every task demands outright speed, in most cases it does mean getting the job done quicker!
The corded or cordless debate has been going on for years, and is likely to carry on a while yet! However, an angle grinder has some very specific power demands, which have a direct impact on your choice.
An angle grinder builds speed very quickly. To do this, it draws a lot of current. If you're plugged into the household electrical system, that's not a problem, but that initial surge is very draining on a battery.
Once up to speed – and it only takes a few seconds – the power demand drops. While you're actually working, there's little contrast between the power demands of the two types. However, every time you stop and re-start work, the battery takes that big hit again.
When you look at performance figures for cordless angle grinders, you'll often see similar numbers to their corded counterparts. In use, however, cordless angle grinders are frequently criticized for a short battery life.
If you need to work where there's no mains power, or where a cable would be a severe hindrance, a high-end, cordless angle grinder is a workable solution, but a spare battery is a must.
A 9" angle grinder packs a tremendous amount of power, but it’s also heavy: 12 to 16 pounds is common. This is another reason they're really only a tool for pros.
The 4 ½” models are much more manageable, usually between four and five pounds. Any lighter than this, and there's a danger that fragile components have been used. It's good to have some weight because it helps balance and steady the tool.
A case isn't a necessity, but it's a nice option.
Angle grinder size can vary by a couple of inches in length, but it doesn't have much impact. However, some have more slender motor housings, which is of benefit to those who have small hands.
As we've said, angle grinders start fast. They can generate considerable kickback, which causes them to jerk in your hand when you pull the trigger. Soft start features are designed to reduce that motion.
Some angle grinders have a lock-out button or switch, to prevent them from starting accidentally.
On some cheap angle grinders, the gears are nylon or hard plastic. A lot of power is transmitted through these components, so metal gears are recommended.
A lot of angle grinder breakdowns are caused by dust and debris getting into the gears or motor. The best models have systems to prevent this.
An enormous range of different angle grinder attachments is available, from diamond-encrusted wheels for cutting tile, to lambswool bonnets for polishing auto paintwork, and chainsaw-like devices for carving wood.
It's vital to use the right wheel for the job. Steel grinding wheels clog in stone. Stone cutting wheels probably won't put a scratch on a metal bolt. You won't save money, and a shattered wheel could cause you serious injury.
Entry-level, 4 ½” models from reputable manufacturers can be found for as little as $25, so it's possible to buy a cheap angle grinder and still get a good, reliable tool.
Price goes up pretty much in line with power, but you can still get a top DIY angle grinder for around $100.
If you want cordless, there's quite a premium. A cased kit with spare battery and charger will be $300 or more. To be fair, if you have a number of cordless tools from the same manufacturer, batteries may be interchangeable.
Pro tools – the 7" and 9" angle grinders – cost around $250.
An angle grinder is probably the most powerful handheld tool you'll own. A cutting wheel rotating at 10,000 rpm can do a lot of damage, so you need to be careful.
Always wear goggles.
Wear ear defenders.
Wear a face mask.
Wear gloves.
Make sure you have a firm grip, and beware of kickback when you start.
Whenever possible, use the auxiliary handle as well as holding the body.
Think about the debris and spark path before you start work.
Never remove the guard.
Always make sure the disk has come to a complete stop before putting the angle grinder down.
Always unplug the tool when changing disks.
Check that the new disk is tightened properly.
Never use a chipped or cracked disk.
For precise cutting, consider an angle grinder stand.
The only maintenance an angle grinder normally needs is a wipe down after use. You should always check manufacturer’s instructions, though.
Make sure whatever you're working on is securely clamped. An angle grinder's wheel speed can easily dislodge or even throw your workpiece.
Never start the angle grinder with the wheel resting on the workpiece. It can induce severe kickback.
