Angle grinder

Angle grinder discs can cut, sand, polish, grind down, tool wood & metal.

Disc Types

Grit Discs

Common cheap discs used for stone & metal cutting & grinding. Cutting discs are thin (typically around 2.5mm), grinding discs are thick (around 6mm or so).

Diamond discs are recommended instead of grit, as performance is vastly superior.

There are however occasional tasks where these grit discs can perform better.

• grinding HSS tool steel
• accessing tight spots using a small worn down grit disc

Main types of grit disc:

• Stone cutting
• Stone grinding
• Metal cutting
• Metal grinding

Other types:

• Stainless steel cutting
• Extra-thin (1mm)
• Aluminium & copper cutting
• See-through discs (large cutouts enable view of workpiece during use)
• Flexible backing pad + fibre abrasive disc for sanding
• Flap discs
• Zirconium flap discs

Diamond Discs

Diamond Discs give a huge performance improvement on grit discs for nearly all tasks, and are now affordable to more or less all angle grinder users.

• Performance far superior to grit discs
• Even basic ones will outlast at least a couple of dozen grit discs
• Safer than grit discs, as a steel disc will not fly apart

Cutting Discs

• Standard thin blades for cutting.
• Available from a few pounds each

Diamond Grinding Discs

• Diamond grinding areas on one side of the disc
• Not cheap
• Available with 1 or 2 rings of abrasive
• Discs are heavier than other types

Tile Cutting Discs

These have no thermal expansion slots. If worked hard without cooling they will heat up and buckle.

TC Grinding Discs

A cheaper equivalent to diamond discs, harder than grit discs but not as hard as diamond.

Wood Discs

Discs designed to tool wood.

Sizes

1"

• 1" - 1.5" abrasive dics are used on die grinders (aka dremel tools).

4"

4.5"

• The most commonly used size for diy
• Wide range of discs easily available for 4.5" grinders

5"

9"

• Large size for cutting deeper.
• Gyroscopic effect affects controllability

Safety

Sparks

Angle grinding discs produce huge quantities of sparks, and good eye protection should always be worn. Direct vent goggles allow sparks to enter the eyes, indirect vent are needed.

Fools can be identified quickly on any site: people refusing protective eyewear when using an angle grinder are a risk to work with, and should be kept an eye on.

Sparks should be kept away from flammables, such as dry sawdust, and windscreen glass, into which the sparks can embed themselves leaving minor permanent damage to the glass surface. Sparks from metal cutting also stain concrete. Nothing is visible initially but as the sparks rust the staining soon appears.

Sparks must also be kept away from the eyes of passers by. Failure to do so can cause injury and/or result in legal problems and costs.

Control

An issue with angle grinders is their ability to go out of control, jump at you and bite off a lump of flesh. Forces on the grinder result from friction between disc and workpiece, which result either from pushing the tool too hard or not controlling its position accurately enough. In other words the best way to reduce risk is very careful control of position, and not pushing it in a rush.

Control of position means always use 2 hands, don't overreach, and ensure a stable standing position, and don't let it wobble in use. It can be tempting to reach out for that last bit, but really its a mistake. These tools have 4.5" 11,000rpm cutter discs with little safety guarding, and you don't want to have a fight with one. You will definitely lose. Which bit you'll lose is anyone's guess.

Keeping yourself out of the plane of the spinning disc much reduces the risk of being bitten by kickback.

The Power-up Gotcha

If you plug it in and the switch on the grinder is on, it will spin, jump & bite.

Reducing risk:

• Check switch position before applying power
• Steel toecap boots
• Use a soft start grinder

Unidentified Flying Objects

Angle grinders generate unidentified flying objects at times, hence the need for eyewear. The objects are usually identified afterwards, but move too fast to be identified while flying.

Face should be kept out of the plane of the disc, as this is the direction in which flying objects and broken discs are launched.

To avoid UFOs, dont push the machine too hard. This is usually what causes them. Push it a bit, the disc grabs the workpiece, and the direction it moves forces the machine hard into the workpiece, and the machine throws.

Petrol driven machines behave much better in this respect, as they have a clutch, but electric grinders have nothing that will slip, plus the inertia of a kilowatt or so of mains motor doing 11,000rpm, so the throwing force is too high to control.

Grind vs Cut

Don't use cutting discs to grind. They aren't tough enough to take side loads and are made even thinner by the grinding process. If you grind off the abrasive side they may shatter and launch a fleet of sharp abrasive flying objects. If you grind off the mesh side they can explode and cause serious injury.

Speed ratings

All grinding wheels have a speed rating. This should not be exceeded in use. Exceeding speed ratings puts more force on the wheel than it is designed to take. Discs coming apart at 11,000rpm is a known issue with grinders.

Especially stupid would be putting a 6,000rpm disc in an 11,000 rpm machine. Yet 6,000rpm discs are on sale and some people do put them in 11,000rpm machines.

Diamond discs are much safer than grit discs in this respect.

Wrong Discs

Never use bench grinder discs, or any other disc not designed for an angle grinder. These other discs lack the explosion control bonded fibre mesh that angle grinder discs have, and generally will not survive the high spin speed, resulting in explosive failure. People have died mucking about with the wrong kind of disc.

Grit damage

Diamond discs throw removed grit so fast it can be hard on skin. Tough gloves & arm coverings are recommended.

See Also

Angle Grinder article

Angle grinder safety

Discussion of disc types

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