E. J. Tangerman - Whittling and Woodcarving

SHARPENING does not waste time, but saves it, for sharp tools cut far faster and easier (thus more accurately) than dull ones. The stone itself, coarse or fine, must be composed of sharp-edged gritscoarseness alone does not mean fast cutting.

Sharpening a tool comprises four operations: grinding, whetting, honing, and stropping. Grinding produces a fine saw-tooth cutting edge, usually with a feathery end of turned metal ( b), the wire edge, clinging to it. This must be removed and the size of the saw teeth reduced as much as possible. Whetting gives finer saw teeth, honing still finer ones, but still the wire edgemuch finer now to be surepersists. Stropping straightens out or breaks off these last saw teeth and removes the final wire edge. Once very fine saw teeth are produced, all four operations need not be gone through continually. Frequent stropping and less frequent honing will retain the edge until it is too blunt to cut well.

Either the old-fashioned, large-diameter, slow-speed, water-dipped grindstone, or the newer, smaller, faster emery wheel can be used for grinding, which is required only on new tools, broken edges, or those that have had a long period of service. The emery wheel shapes a tool faster, but will burn it if it is not dipped into water often. It is far better in this instance to be safe than sorry, for too much water never ruined a tool, and too much grinding heat will. It draws the temper, giving a soft tool end.

Tools should always be ground on the wheel periphery, with the wheel turning toward the cutting edge. If an emery wheel, it should not be too coarse. The periphery should be clean and square and kept that way by regular dressing with an emery stick, a bit of broken wheel, or a diamond dresser. Otherwise the wheel will load with bits of groundoff steel, will glaze and burn the tool. A crooked surface produces a crooked cutting edge, too. If the wheel has a tool rest, use it, and while sharpening, move the tool across the face of the wheel, thus wearing it evenly.

How to sharpen and test a knife: Paper and tip tests for sharpness

A broken or poorly shaped cutting edge should first be fed perpendicularly to the wheel to square it up. Then grind the bevel, which properly should vary with the hardness of the wood you plan to cut. A thinner cutting edgeone with a smaller included anglecuts through wood more easily, but hard woods dull it so rapidly that a thicker edge is advisable. About 15 to 20 degrees included angle ( a ) is suitable for tools to cut soft woods; 20 to 25 degrees gives the edge more support in hard woods.

When you grind an edge, hold the tool carefully at the proper angle and move it perpendicularly to the wheel ( b), giving a little relief just back of the cutting edge that will make the tool hold its edge longer. Chisels and other single-ground tools are ground from the bevel side only, firmers and axes from both sidesin the latter case very evenly to be sure the cutting edge remains at the center of tool thickness.

Gouges must be rotated evenly from side to side (by a wrist-twisting motion) during grinding, so that the whole curved face is cut away evenly. Work carefully, or the corners will be ground away, putting them behind the bottom of the U, and the tool will have a tendency to stick. One gouge, say a -in. one, may be ground this way intentionally for use in cleaning up a ground close to a cornerbut dont do it with the others.

Whetting and honing should really be considered together, for the processes are exactly alike, the difference being in the coarseness of the stone. The natural or quarried whetstone is Washita, yellowish, or grayish, and slow-cutting. The natural hone is Arkansas, a white, extremely hard, fine-grit stone that produces an exceptionally fine edge. If preferred, the two may be obtained together, with Washita on one side and Arkansas on the other. Manufactured stones of silicon carbide or aluminum oxide grits, such as Carborundum, are similar in appearance and cutting effect.

How to sharpen and test firmers: Nail and chamfered-corner tests

Good machine oil, or a fifty-fifty mixture of machine oil and kerosene, is used as a lubricant to prevent loading of the stone. Move tools in straight lines parallel with the axis of the stone. Only in this way can you keep the surface flat and square. If it gets out of square, grind it on the side of a grindstone, or rub down with sandstone or an emery brick. Cover stones when not in use, and keep them clean and moist with a few drops of oil. Clean natural stones by periodic washing with benzine, kerosene, or gasoline, or boil in water containing a little soda. Clean manufactured stones by putting them in a tin pan and heating in an oven. (This causes the old oil to be exuded.) Then wipe it off hot.

Gouges, parting tools, etc., must be finished inside with a slip or shaped stone. This is laid inside the curve or V and rubbed o utward to remove wire edge. Some carvers lift the back end a little to produce a very slight bevel. Rest the tool on the bench with the edge projecting an inch or two for the stoning ().

Stropping is done on smooth leather, just as for a razor, except that many carvers use two strops, the coarser covered with a paste of crocus powder in oil, the second with a little oil only. Here is the second exception to the rule of sharpening against the cutting edgealways trail the edge on the strop ().

How to sharpen and test a gouge: . Stropping. FIG. 452 Various shapes of slips

Now to specific tools: Unless nicked or broken, the knife blade is never put on the grinding wheel. Its wedge shape provides proper clearance and support for the cutting edge without shaping. The blade is always sharpened on a flat stone (). Whet and strop all the way back to the heel on both sides, and give the tip a bit extra.

To test for sharpness, draw the edge across your thumbnail ( b ). It should cut in easily, without pulling. Stainless-steel blades are harder to sharpen, but hold an edge longer.

Firmers and chisels are sharpened similarly, except that the edge is pushed the length of the stone instead of being held from the side. Hold the blade at an angle of 20 to 25 degrees with the surface of the stone ( a ), otherwise it will tear the wood instead of cutting.

Parting tools and scrapers: Turning scraper edge

Usually any woodcarving tool can be kept sharp for a long time if you habitually strop, or hone and strop, it while you plan the next cut. A little practice will teach you how. Whet a chisel on the bevel face, finishing with a light stroke or two on the flat face to remove wire edge. It is best to fasten the stones and strops down, as in ).