The Secrets of Tool Sharpening

To get the best performance possible from the bladed implements in your kitchen and workshop, here is how MOTHER EARTH NEWS' researchers go about the job of tool sharpening.
By the MOTHER EARTH NEWS editors
July/August 1981
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With this assortment of hand-held tool sharpening devices and a bit of patience you can put an excellent edge on a knife, but for other tools they're less practical. Pictured on the top row from L to R are a soft Arkansas stone, buck sharpening steel, Smith hard Arkansas stone, and a Gerber sharpening steel. Below in descending order are a sharpening steel for stainless, sharpening steel for high-carbon, and a ceramics stick.
PHOTO: MOTHER EARTH NEWS STAFF
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There are few experiences more frustrating than attempting to work with a dull tool, but keeping keen edges on the average household's supply of bladed implements can be a very time-consuming task. Consequently, we'd like to pass on a few of the time-saving methods our workshop brigade uses to keep its (sizable!) stock of equipment well honed.

A Versatile Edge

After working with a variety of different edge designs, we've come to favor a multi-angled taper for most of the shop tools and heavy-duty knives, while we prefer a rounded version of the same edge for kitchen cutlery.

Of course, other blade configurations are well-suited to specific tasks. Hollow-ground knives, for example, will slice food more easily than will blades with our preferred edge, but the former grind's loss of strength limits its usefulness for many purposes. In fact, we're inclined to think that hollow-grinding has only three legitimate applications: on carving knives, on decorative knives (it does enhance the appearance of a blade), and on flathead screwdrivers (where the relief helps the tool reach deeper into a fastener's slot).

The specific angle to which a tool is sharpened should be determined by the duties that the implement must perform.

Wood chisels, planes, and similar shop items need a medium angle (about 30°) to peel back layers of wood, for example, whereas cold chisels, axes, and other heavy-duty implements need blunt angles if they're to resist chipping.

It's a good idea to let the intended task determine the edge angle when sharpening knives, too. A fine carving tool, for example, might get by with a very steep angle to let it glide through a Thanksgiving turkey. However, a pocketknife honed to a similarly severe edge would never survive being used to punch holes in can lids, cut wire, or any of the other not entirely appropriate tasks such tools are regularly asked to do.

A Quicker Way

With a little patience, you can use hand-held sharpening devices to put an excellent edge on a knife. But when you're honing other tools, the manual sharpeners often aren't practical.

So, to handle the variety of implements in our workshop—and to put an edge on knives quickly—we built a belt sander. With it, our researchers can finely hone just about any tool in a matter of minutes.

The grinder is made of three 1 1/2"-wide, 6"-diameter casters, a slow-speed (1,050 RPM), 1/4-horsepower motor with one of the casters attached to its shaft, a frame to connect the pieces, and a 1"-wide sanding belt. (The belts we use are sold as crankshaft polishing items, and are available in grits as fine as 400. However, we've found that the worn 320 belts discarded by our local auto machine shop work quite well, and the price is right!) The working surface atop the sander's frame is built from oak (to resist wear), and an open area has been left in the center for doing fine work.

The Procedure

To show you how the device is used, let's run through the steps needed to renew a really dull kitchen knife, perhaps the most difficult sharpening job of all. But first, consider the lighting in your shop area. It's very hard to do a decent job of sharpening without adequate illumination. MOTHER EARTH NEWS' toolsmiths recommend working with an incandescent light shining directly over the shoulder of the honing hand.

STEP ONE: Establish the taper. Knives that are badly worn or have been ground incorrectly (you'd be surprised how many are inconsistently set at the factory) need to be filed to a balanced taper of 10 to 15° per side. We use the finest-toothed file available, and stroke the blade very lightly. In this step—and in each subsequent one—only one stroke is made per side before turning the blade over.

STEP TWO: Smooth the taper. Now we go to the belt sander, to smooth out the file marks from the blade—using nothing more coarse than 240 paper—by resting it lightly on the wood-backed portion of the belt at the 10 to 15° angle. If at all possible, we orient the blade so that the belt is moving toward the edge to reduce the burr which inevitably forms during grinding. In addition, we keep the knife in constant motion across the belt and turn it over frequently.

STEP THREE: Blue the blade. The coloration helps to show just where the edge has been ground. (We often use a wide felt tip marker for this task because it's easier to use than is machinist's bluing.)

STEP FOUR: Establish the edge. At this point, it's time to grind the edge to the desired angle. Again, the blade is moved against the wood-backed portion of the belt, but it's now held at the finished angle. The bluing makes it much easier to judge our progress during this stage.

STEP FIVE: Smooth the new edge. The gloved left index finger (assuming the person is right-handed) is slipped beneath the belt in the center section, and the blade is worked against the abrasive surface backed by a sensitive finger tip.

STEP SIX: Strop. To remove the burr that forms along the edge, we tack the tip of a worn belt to the edge of the table, hold the loose end out with the left hand, and draw the blade back and forth across the abrasive surface. A check with a fingernail—pulled perpendicularly past the edge—will tell you whether or not the burr is gone.

STEP SEVEN: Finish. Even a worn 320 belt will leave scratches in steel, which will make a blade more susceptible to corrosion. So we finish our cutlery with a ceramic stick (a soft Arkansas stone—without oil—will do the job, too). The edge is slipped along the rod's surface as if one were attempting to slice off a piece of stick. With one stroke per side, the pressure is gradually lightened as the blade moves more and more easily against the ceramic.

Other Tasks

Our homemade belt sander has proved to be quite useful for maintaining everything from scissors to screwdrivers. We fabricated a rest—from a 3/8" X 10" carriage bolt—next to one of the wheels so that different tools could be held easily at their preferred angles. The arc of the caster also happens to be ideal for hollow-grinding a screwdriver.

Depending on how worn an implement is, it can be returned to top-notch shape—using the procedure detailed above—within three to five minutes. That's a small price to pay for a tool that works!


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