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The bench grinder is the enabler of a household workshop. Sure, it's not going to be the fanciest tool in the shed, nor the most expensive, but that doesn't mean it's not the most important. Put simply a bench grinder will elevate the rest of your toolset, providing sharpened blades, edges and chisels as well as smoothing the edges of any objects you're working on.
From small household tools to large industrial grade equipment, bench grinders, like most tools, come in all shapes and sizes. For most DIY sheds, a bench grinder will be about the size of a shoe-box. Housed in the bench grinder, you'll find two wheels that are treated with bonded grit.
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The type of grit will depend on what you're using it for. For grinding steel you'd use Vitrified Aluminum Oxide. For non-ferrous materials like copper, or brass you'd fit a White Quartz Sand wheel. Normally, you would expect about 90 degrees of that wheel to show, the rest is encased within the unit.
The wheels are linked to a small motor that, when ignited, will rotate the wheels at 3,000 to 4,000 revolutions per minute. One quarter of a horsepower should be more than enough for a small workshop. The spinning, gritted wheels can then be used to smooth, or sharpen, the edges of plane irons, wood and cold chisels, drill bits, knives and scissors. A bench grinder can also repair screwdrivers and punches, smooth rough welds and grind off rivets. If you replace the gritted wheel with a buffer you can use it to clean, or polish, all sorts of tools and objects.
The premise of a bench grinder is relatively simple and works much in the same way as using sandpaper. The treated wheels act like thousands of tiny knives which reduce contact material into dust. Placing the edge of the object against the spinning wheels, the user applies consistent pressure to smooth, or sharpen the selected object. The engine is engaged via a foot-pedal to allow the user full control of both arms when engaging the bench grinder.
Bench grinders are designed to grind down even the toughest materials. You can make a chisel disappear in minutes so, it goes without saying, always keep your hands well away from the wheels when the engine is engaged. Small filaments and metal dust will spray off when grinding metals so always wear safety goggles to protect your eyes.
Before every use, you should make a check of the wheels on your bench grinder. To check the grinding wheels take a solid, metal object and tap the wheels. You should hear a ringing sound. If, when you tap the wheel, you instead hear a dull thud, the wheel may be cracked and needs replacing. Grinder wheels spin rapidly so the slightest structural damage can result in the wheel itself shattering. Needless to say, a damaged wheel could lead to a very dangerous situation.
The type of wheels that you use will determine the type of job the bench grinder is suited for. Typically a bench grinder will have on wheel treated with a coarse grit, and the other with a finer grit. The coarse grit is for heavy-duty projects, ironing out chinks or cracks in the object. The finer grit is used to sharpen existing tools, or for polishing purposes.
The grinding wheels themselves, are often fragile so always place the bench grinder in a quiet corner of the workshop. That way you can avoid costly replacement wheels from accidental damage.
If your primary use of a bench grinder is for woodwork, you may want to consider an aftermarket tool rest which will allow you to get those finer bevel angles. When it comes to woodwork it's well worth investing in a friable wheel. The standard wheels on a bench grinder will run far too hot for wooden tools so opting for an aluminum oxide or ceramic alumina will pay dividends.
That just about wraps it up as far as the bench grinder is concerned. It's not the most sophisticated tool in the workshop but it's a must-have for those serious about DIY.