Woodworker's Journal 2001-25-2, страница 32

the wood surface will be scored with ridges. Also, with harder wood, the micro teeth will quickly break off. blunting the cutting edge. In other words, the flatter and more polished the faces, the sharper the cutting edge — and the longer it will stay sharp.

Whatever abrasive you choose, the starting grit is determined by the condition of the back face of the blade. Since new blades require the most work, start with the coarsest grit. Remove all the manufacturer's marks at the outset or else they will haunt you at later stages. The more pressure you apply, the faster the cut rale. Place the abrasive on a solid surface and work the blade with arms extended to add the weight of your upper body. First-time flattening jobs can be a lengthy chore, so you may prefer to sit on a high stool.

To flatten and polish the back face you could use any one of a combination of oil stones, water-stones, diamond plates, coated abrasives, and diamond paste.

Oil Stones: Oil stones were once the primary method of sharpening tools. They're still manufactured and mined and, because they resist wear, there are still plenty of them around.

There are three basic types: Carborundum and Crystolon, gray color and made of silicon carbide; India, reddish-brown color and made of aluminum oxide, and a variety of natural stones; such as Hard and Soft Arkansas. If you have inherited some oil stones, they will almost certainly need flattening. Then, store them properly.

Check flattening progress with a 10X hand lens to confirm that you have replaced one set of marks with a set of finer marks.

Apply diamond paste in small spots to the MDF carrier plate. Identify each plate by grit size to prevent contaminating one si2e with another. For the same reason, wipe the blade thoroughly before moving to a finer grit.

Squelch and spread the diamond paste the length of the plate before starting to polish. The pastes come in different colors, but they all turn black In use.

Waterstones: Walerstones imported from Japan began to displace oil stones about 20 years ago. Although they wear more quickly than oil stones, they cut faster, and the finest grit produces a highly polished surface. The abrasive is aluminum oxide held in a soft bond of fine silica. The grit range of Norton stones is 200x, l.OOOx, 4,000x, 8,000x.

Waterstones are readily available as singles, combinations, or packs of four. Properly-cared for, they will last the average woodworker for many years and are well worth the investment of S50 a stone.

Coated Abrasives: A coated abrasive consists of abrasive grains bonded to a backing by an adhesive. Those suitable for sharpening blades are composed of either aluminum oxide or silicon carbide bonded to paper, cloth, or polyester film.

Woodworkers routinely sand wood with aluminum oxide papers. Although the same product can be used for flattening the backs of blades, a better choice is the cloth-backed product designed for metalworkers. I use Metalite aluminum oxide cloth, available in 8V x 11" sheets, specifically formulated to cut steel. It's "closed coated," which means the abrasive grains completely cover the backing. The "open coated" woodworkers' product has about 50 percent coverage.

Metalite^- comes in many grits, ranging from 8Ox to 600x. The cut is so aggressive at the coarser end that you may wish to wear work gloves. Coated abrasives in grits l.OOOx and

32

April 2001 Woodworker's Journal