The bench grinder is an essential shop accessory for sharpening turning chisels, putting a new edge on badly nicked plane blades and bench chisels, grinding drill bits, and for a range of other metal grinding, shaping and polishing tasks. It will also keep your garden tools in top cutting condition.
Essentially, a bench grinder removes metal by means of an abrasive wheel (or ‘stone’). Most grinders have an induction motor with spindles mounted on each end of the motor’s armature. The grinding wheels are attached to these spindles. Wire wheels, buffs and polishing discs can also be mounted on the spindles. Generally, grinders also come with some kind of tool rest and spark guard.
Grinders are rated by their wheel size, with 6″ and 8″ wheels being the most common. The wheels come in course, medium or fine grits. Typically, 6″ grinders have ½ to ¾ HP motors, and 8″ grinders have ¾ to 1 HP motors. The motors run at high speeds, usually around 3,450 RPM.
The most common kind of grinder is a ‘dry grinder’ or a ‘double end grinder’ to distinguish it from a ‘wet grinder’ (which uses a waterstone wheel and water as a coolant and lubricant) and a ‘slow speed grinder’ (which runs at a much slower speed, of around 1,700 RPM).
In general, you can use turning tools and drill bits straight from the grinder. For bench chisels, plane blades and the like, you follow up grinding with honing on bench stones.
Most grinders are supplied with inexpensive carborundum wheels, typically a coarse 36 grit wheel and a medium 60 grit wheel. These wheels work fine for sharpening garden tools, but are really not suitable for the needs of woodworkers. They are slow cutting and become dull and glazed quickly, causing tools to overheat. While this may not be critical when sharpening an axe, if you’re re-grinding the bevel on a turning chisel, excessive heat can ruin the temper of the chisel (making it soft and reducing its cutting properties).
Upgrading to higher quality, soft bond, open structure aluminium oxide wheels, is highly recommended. Because these wheels wear faster, you can sharpen faster, with less danger of taking the temper out of the tool. Unless you are a professional wood turner or mechanic using your grinder everyday, a new set of wheels should last a long time.
Wheels don’t have the same density throughout their structure, and they can vary in thickness. As a consequence they vibrate when turning. Cheaper wheels tend to vibrate a lot more. Unbalanced wheels make it more difficult to achieve a uniform grind on tools, they can damage the bearings over time, and they reduce the life of the wheel because they have to be trued (or dressed) more frequently.
A common complaint with grinders is that the toolrests tend to be small and flimsy. It’s important that the toolrest be rock steady, and have a large enough surface to adequately hold the tool that you’re grinding. Otherwise you’ll find it difficult to create a consistent bevel on chisels and plane blades. A steady toolrest also makes for safe grinding. To see if your toolrest needs replacing, press down on it with your fingers – there should be no flex.
The King Canada grinder (model KC-890), at $79.99, is good value in a basic, no frills, bench grinder. It has a direct drive motor with permanently lubricated bearings, and takes 8″ wheels up to ¾” thick. Its heavy weight (36 pounds) helps reduce vibration. The carborundum wheels on this grinder are quite coarse, and the toolrests are rather flimsy affairs. They’re much too small (1 ⅛” x 2 ¼”) to support any but the very smallest woodworking tools, and they flex quite a bit. However, with a few embellishments from Oneway Manufacturing we’ll turn the KC-890 into a grinder fit for a king’s workshop.
We’ll begin by replacing the stock aluminium oxide wheels on the King with grinding wheels from Oneway Manufacturing. Wheels are easily installed, so we’ll put the King wheels aside to use when grinding our gardening tools. Removing the wheels is straightforward.
The Oneway wheels are of exceptional quality. These are ‘friable’ wheels, which means that the grain in the wheels fractures as you grind, exposing fresh grinding surfaces. Consequently the wheels don’t load up and glaze over as quickly as other wheels, and they don’t heat up the tool as quickly. They’re specifically designed for high speed grinders, like the King, and come in 54, 80 and 120 grits. Because we’ll be using this grinder primarily to sharpen turning tools, we’ll install 54 and 80 grit wheels. At $57.50 per wheel, these are very good value.
Next we’ll balance the wheels, using Oneway’s ‘Wolverine Precision Balancing System”. Sounds complex, but it really isn’t. Balancing takes all of half and hour, thanks to well written and easy to follow instructions. The kit is available for grinders with ½”, ⅝” and ¾” diameter shafts, though the wheels require a 1″ diameter center hole (plastic reducers are included). The kit consists of a stand, axle and bearings, and a two-part flange (a set for each wheel). Once the wheels are balanced mount them on your grinder. At $57.50 this kit is a good investment that will extend the life of your grinder and cutting tools.
The Oneway Wolverine Grinding Jig is the ultimate toolrest. It consists of two heavy-walled aluminium extrusion bases that you mount under each wheel, on top of a plywood platform (user supplied). The bases have cam-lock clamps that serve to hold grinding accessories. The kit also comes with a sturdy 3″ by 5″ toolrest (for grinding scrapers, paring tools and other square end tools), and a 27 ½” long V-arm (for grinding gouges and chisels). The jig is quick and easy to assemble. You do need to make sure that the center of the diamond shaped arm holes of the bases is aligned with the center of the grinding wheels, and that the front edge of the bases are even with the front edge of the wheel. Once this is done you’re ready to use the jig. This jig is very sturdy and rigid, the way a tool rest is meant to be. And at $79.95 you won’t break the bank.