Angle grinders

While hand tools are going to be the basis of your tool kit, power tools are great for speeding up your tasks. Can you cut steel with a hacksaw? Can you remove metal with a file? Sure, but it’s a lot quicker if you use a tool like an angle grinder.

They come in a number of sizes. Let’s talk about each one of them and why they’re useful and what sort of accessories they can be set up with. 

Angle grinders are generally classified by the nominal diameter of the accessories they use. The typical cutting and grinding accessories are described as “abrasive” in nature. They consist of abrasive particles bonded together into a wheel or disk. The materials used and construction of the wheel or disk will depend on the application – discs used for cutting steel will be different to discs used to grindstone, for example.

The abrasive particles “scrape” away material as they spin. Eventually they dull and break away from the bond, exposing new, sharp particles. This means the diameter of the wheel or disk decreases in use, until it is too small to be useful.

The Four-Inch grinder 

Four-inch diameter tools are the cheapest ones you’ll generally find on the market for mass consumption and are well suited to motorcycle tasks.  When you’re using grinders on a regular basis it can be tedious changing accessories all the time. If you buy two, one can be set up with a cutting disk and the other with a grinding wheel or a sanding disk, which will speed up your workflow.  

The Nine-Inch grinder

9-inch grinders are great for heavy-duty jobs like roughly cutting up large steel sections, tube or sheet. There is no “finesse” with a 9-inch grinder, so it’s not suitable for most motorcycle work (other than cutting the frame). Don’t waste your money unless you have other needs for it. “Bigger” is not “better” in this case.

The Five-Inch grinder

This size grinder has turned out to be very useful for one reason: it will cut through 1-inch/25mm tubing from one side in a single cut. This is a common size used on older motorcycles (as is 3/4″ and 7/8″, or 19mm and 22mm for the metric world).

If cutting this tubing using a 4-inch grinder, you might only get three-quarters of the way through and then you have to turn around and cut from the other side. This makes a clean, straight cut more difficult. The accessories are a little bit more expensive, obviously, but they do last a longer than the 4-inch ones. 

Purchase a cheap 4-inch grinder first. If you choose to purchase a second grinder, consider a 5-inch grinder if cutting tube is a common task.

It should also be noted that while corded grinders are most common, cordless angle grinders have grown in popularity and are handy tools with enough cutting power for all relevant bike work. If you are purchasing a cordless grinder and/or cordless drill, consider getting the same brand so the battery is interchangeable.

Grinder accessories

It is the sheer number of accessory (disc/brush) types that you can fit to a grinder (and what you can do with them) that makes it such a useful all-around tool for your workshop.

Cutting discs 

When considering accessories for your grinder, a cutting wheel or a cutting blade is an absolute must. One-millimeter-thick ones are by far the most useful. They allow you to cut through tube cleanly, quickly and with a thin “kerf” (which is the thickness of the cut).  

Sanding disc (flap wheels)

Another very useful accessory is a “flap disk” or a sanding disk. A flap disk is constructed of an array of sanding pads bonded to a backing plate. They are available in a range of abrasive grits. As they are used, the edge of the pad wears away to expose more abrasive.  

100 grit or 120 grit is a great all-around grit for bike work. The coarse grits (40, 60 or even 80 grit) are very aggressive and can remove a lot of metal very quickly if you’re not careful.  

Grinding disc 

Similar to the coarse grit flap wheels, a grinding disc is a very aggressive method of removing metal (even more so than a flap disc).  They are very cheap but use them carefully on your motorcycle.

Wire brush

This should be a go-to tool for stripping paint or cleaning up rust off surfaces. As the wire bristles spin, they smash paint and rust off a steel surface without significant surface damage. Steel bristles are harder than aluminium, so they will damage an aluminium surface. The bristles will remove paint and rust from irregular surfaces and many a garage builders complete motorcycle frame has been stripped back to bare metal with a wire wheel on a grinder.

They come in various shapes, such as flat disc or cup shapes and can have straight bristles or twisted bristles. The twisted versions are much stiffer and have less give to go around protrusions. There are also versions of these available for drills.

Paint stripping discs

These often have proprietary names depending on the manufacturer, but regardless are great for motorcycle work, especially for larger, flatter surfaces, such as fender and gas tanks. With an angle grinder, a paint stripping disc and a wire wheel, you can remove paint from a whole motorcycle. Would it be quicker to send it for sand blasting or dipping? Sure, but you can do it at home at low-cost with these tools.  

You can also purchase versions to be fitted to a drill.

Synthetic non-woven flap discs

Similar construction to a flap wheel, synthetic non-woven flap discs contain a polymer abrasive rather than an abrasive particle pad. Different colors indicate different grades. These are great for final sanding and surface smoothing. They are much less aggressive than a sanding flap disc, so are relative safe to use on aluminum surfaces with less damage.

Grinder use and safety 

Accessories must be matched to the spindle on the angle grinder you purchase. The packaging or instructions will specify the bore (hole in the center of the disc) that fits your grinder. Wire wheels are sometimes supplied with a threaded fitting that screws directly onto the spindle.  

Ensure you center the disc on the spindle and clamp the disc snugly between the inner and outer flanges. You will need the tools provided with the grinder are needed to secure the outer flange nut. Only change discs when the angle grinder is disconnected from, or turned off, at the wall socket.

Bonded cutting and grinding discs are susceptible to impact. If you drop one, you should not use it. If it cracked due to being dropped, there is a risk it will explode when the angle grinder spins it up to full speed. Don’t believe it? Google images for “angle grinder accidents” – if you dare.

Grinders drive the spindle very quickly, and this speed combined with the abrasive cuts or grinds away metal. Don’t press the disk into the work heavily. If you hear the motor slowing down, you’re overloading it, and risk the tool kicking back at you if the disk gets jammed. Let the disk and the grinder do the work.

A lot of YouTube videos show angle grinders being used with the disk guard removed and it makes no sense why people remove these guards. Your fingers are wrapped around the body of the angle grinder less than 2-inches away from a disc spinning at 10,000 rpm. With no guard, you are at risk of a visit to the Emergency Department if the grinder kicks back for you.  

While you are cutting or grinding, showers of sparks (which is burning carbon) and small shards of metal fly. To protect your eyes and lungs from this airborne debris, wear a disposable dust mask. Although you might not think it, hearing protection is also highly recommended when using an angle grinder even for short periods. Hearing loss is a cumulative issue.

All that airborne metal and carbon will settle on surrounding surfaces, so protect vulnerable items like disassembled engines, transmissions, and carburetors from ingesting this nasty stuff, as the metal particles will eventually begin to rust. Move these parts or cover them while you’re working.

Finally, it’s wise to check for fire hazards before you start cutting or grinding. Look for chemicals, gasoline, oil, paper, cardboard, or fabrics such as rags. It’s easy to accidently divert sparks into your clothes and burn yourself! Wire wheels will start ejecting wires after heavy use. They can be found embedded in your clothing in unusual locations at inopportune times while you’re working. Cover your arms and legs with heavy workwear to provide maximum protection.