Sharpening With Waterstones

More and more woodworkers are finding that the path to perfectly sharpened edge tools leads them through water. For that's what lubricates the increasingly popular Japanese waterstones. These man-made whetstones offer a big advantage in sharpening tools—an abrasive surface that constantly renews itself as you work.

A waterstone's soft abrasive particles break off in use, constantly, exposing new, sharp edges. As you continue sharpening, those broken-off crystals crumble into smaller and smaller pieces. The crumbled crystals mix with the water on the stone's surface, creating a slurry-in effect, a honing and polishing compound.

Compare this with what happens to the hard abrasive particles that make up many other kinds of whetstones. Instead of breaking off through use, they round over and become dull. At the same time, oil residue and metal particles pack into the stone's pores, glazing the surface and reducing the stone's ability to produce a really sharp edge.

Japanese waterstone grades cover a range from 150 to 8000 grit, but those numbers don't relate directly to U.S. grades. For example, the abrasive action of a Japanese 150-grit stone approximates a 100-grit U.S. one; the Japanese 1000, a U.S. 500; and the Japanese 4000, a U.S. 1000. It's better to relate waterstone grades to each other than to try converting them to U.S. grades.

Here are some points that will help you when buying waterstones:

• To remove a lot of metal fast, for restoring a damaged edge or changing a blade's bevel, for instance, you'll want a waterstone in the 150- to 250-grit range.
• You can count on an 800-, 1000-, or 1200-grit waterstone for general-purpose sharpening. The 800-grit stone is a good all-around choice if you sometimes have to sharpen nicked or heavily used edges.
• For honing and polishing a sharpened edge, select a 4000-grit or finer stone, sometimes called a finish stone.
• A pair of stones will suffice for normal tool sharpening—an 800, 1000, or 1200 and a 6000 or 8000. If you often deal with damaged edges, add a more aggressive 150- or 250-grit stone to your set.
• Individual waterstones cost from $20-$40 on average, with some ultrafine (8000-grit) finish stones running as high as $75. You can buy combination stones, with a coarser grit on one side and a finer one on the other, for $25 to $50.

Waterstones are intended to be used wet. So before sharpening, soak the stone for 10 to 15 minutes in clean water. (We bathe ours in a drywall-compound tray, shown below. You can use any small pan deep enough to submerge the stone in.) While sharpening, keep the stone's surface wet. (We squirt water on the stone from a bicyclist's water bottle; any squeeze or spray bottle would do the job.)

All the water, along with the slurry of abrasive and steel particles that forms on the stone's wet surface, makes sharpening messy. To contain the mess and protect your benchtop, place the stone on a cookie pan or similar shallow tray. Hold the stone in the center, using spacer blocks or a simple fixture like the one shown in the illustration above and the opening photo.

For better sharpening and to protect the stone from accidental gouging, always hold the tool in a sharpening or honing guide, as shown in the opening photo.

Some woodworkers store waterstones in water-filled buckets or plastic boxes. That's okay for coarse and medium stones, but not for fine-grit finish stones. They should be stored dry.

We prefer to store all waterstones dry—or maybe damp would be a more accurate adjective. It's less hassle: You don't have to stash sloshy boxes of water in your shop, and you won't end up growing odd organisms if you fail to change the water often enough.

After use, just rinse the stone, pat it dry, and stick it into a lidded plastic box. (The stone will remain damp for a while, so keeping it in the original cardboard box isn't practical.) Protect waterstones from freezing temperatures—water that remains in a stone can freeze and crack it.

Sharpening plane irons, chisels, and other tools calls for a flat stone. But, because sharpening action constantly shears abrasive particles from the waterstone, its surface can become dished. It's easy to flatten a stone again, though. Here's how:

Place a piece of 120-grit wet-or-dry sandpaper, abrasive side up, on a piece of glass or some other true, flat surface. Wet the sandpaper, then rub the stone on it in a figure-8 motion. Check the stone's face with a straightedge.

Flatten your waterstones after every few uses, rather than waiting for them to become noticeably dished. Even if you flatten a stone after every use, it will still last a long time.