The Secrets of Tool Sharpening

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So, to handle the variety of implements in our workshop-and to put an edge on knives quickly-we built the belt sander that's shown in Photo 2. 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 (1,050RPM), 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 . . . but 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 . . . and MOTHER's 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 (Photo 3). 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 (Photo 4). 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 felttip marker for this task-see Photo 5 -because it's easier to use than is machinist's bluing.)

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