Angle grinders can be powered by an electric motor, petrol engine or compressed air. The motor drives a geared head at a right-angle on which is mounted an abrasivedisc or a thinner cut-off disc, either of which can be replaced when worn. Angle grinders typically have an adjustable guard and a side-handle for two-handed operation. Certain angle grinders, depending on their speed range, can be used as sanders, employing a sanding disc with a backing pad or disc. The backing system is typically made of hard plastic, phenolic resin, or medium-hard rubber depending on the amount of flexibility desired.
Angle grinders may be used both for removing excess material from a piece or simply cutting into a piece. There are many different kinds of discs that are used for various materials and tasks, such as cut-off discs (diamond blade), abrasive grinding discs, grinding stones, sanding discs, wire brush wheels and polishing pads. The angle grinder has large bearings to counter side forces generated during cutting, unlike a power drill, where the force is axial.
Angle grinders are widely used in metalworking and construction, as well as in emergency rescues. They are commonly found in workshops, service garages and auto body repair shops. There is a large variety of angle grinders to choose from when trying to find the right one for the job. The most important factors in choosing the right grinder are the disc size and how powerful the motor is. Other factors include power source (pneumatic or electric), rpm, and arbor size. Generally disc size and power increase together. Disc size is usually measured in inches or millimetres. Common disc sizes for angle grinders in the U.S.A. include 4, 4.5, 5, 6, 7, 9 and 12 inches. Discs for pneumatic grinders also come much smaller. Pneumatic grinders are generally used for lighter duty jobs where more precision is required. This is likely because pneumatic grinders can be small and light yet remain powerful, because they do not contain heavy copper motor windings, while it is harder for an electric grinder to maintain adequate power with smaller size. Electric grinders are more commonly used for larger, heavy duty jobs. However, there are also small electric grinders and large pneumatic grinders.
Through a sound pressure level and vibrations study conducted by the National Institute for Occupational Safety and Health, grinders under an unloaded condition ranged from 91 to 103 dBA. In addition, angle grinders produce sparks when cutting ferrous metals. They also produce shards cutting other materials. The blades themselves may also break. This is a great hazard to the face and eyes especially, as well as other parts of the body, and as such, a full face shield and other protective clothing must be worn. Angle grinders should never be used without their guard or handle attached; they are there as a necessary precaution for safety. All work should be securely clamped or held firmly in a vice.