Creative Woodworks & crafts 2001-08, страница 40

Sharpening Carving Tools

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by Ivan Whillock

Most carvers know that sharp tools are more efficient and safer than dull tools. Many beginners find that the hardest job in carving is sharpening tools. Unfortunately, a tool that is considered sharp by a beginner might seem quite dull to a professional carver.

Years ago. it was uncommon lo buy factory honed carving tools. They were ground to an exLent, but much work was left for the carver to do. Most carvers bought a new tool and worked the edge to their preference. These days, more and more carving tools are sold factory honed, nearly ready to go. At that, most trained carvers will regrind them or at least "touch them up," putting the exact edge on them that they prefer. Even in these days when factory honed tools arc readily available, it is a good idea for carvers to be able to sharpen tools from scratch. Besides, through use or mishap, even carefully ground tools may have to be reground.

Some Basics

Because I use the traditional two-handed style of wood carving, I grind my tools to a 20 to 25 degree angle (see Fig. 1). It is also important to keep the bevel flat. Holding the tool square against a grinding wheel creates a hollow ground (see Fig. 2). There are two ways to diminish the hollow grinding. One is to move the tool up and down on the wheel to cover the entire bevel. The other is to hold the tool at a slight angle to the wheel (see Fig. 3). Thus, the flat side to side dimension of the wheel minimizes hollow grinding. While the tool is being ground, it is rotated side to side to cover the entire bevel of the tool. Also, whenever the tool feels slightly hot it is dipped in water. High carbon steel, great for holding an edge, cannot take heat. If the steel turns blue, the temper is gone and the edge must be reground.

Of course it isn't necessary to use a machine for sharpening (sec Fig. 4). Many professional carvers I know do all their honing by hand on stones. (The hobby carvers are the ones who have the fancy sharpening machines!) When using a stone, move the tool side to side, freezing your wrist into the proper angle for the degree of bevel you desire. Along with the side to side motion of your arm, also rotate the tool to cover the entire bevel. Putting your finger on the end will help you feel whether the full bevel is against the stone. You will soon get the feel for the proper angle. Check your progress often to make sure you are grinding evenly throughout the whole bevel. Return the tool lo the stone each time at the exact angle so that you grind a single flat angle on the tool. While you can do all of your grinding on a single fine stone, it is much faster to have two or three stones of different grits. As we discussed in an earlier column, there are many choices for stones: oil, water, diamond, ccram-ic. I like a coarse stone for the first stages of shaping, a medium to clcan up the coarsc stone marks, and a fine Arkansas stone to begin the polishing. Final honing is done with a strop.

Treat the V tool like three tools (see Fig, 5). Sharpen the sides like a chisel. Move it. side to side on the stone with your wrist frozen into the angle you desire. Unlike with the gouge, you do not rotate your wrist. Turn the tool over from time lo time and work the same angle on the other side. Be very careful in keeping the outside bevel parallel to the inside plane of (he tool. This is the biggest challenge in sharpening a V tool. Now sharpen the bottom of the V as if it were a gouge, rotating it as you move it side to side on the stone (see Fig. 6). It is very important that the bottom angle of the V tool is about the same degree as the sides. Also, inspect the inside

of the V tool. If the bottom of the V is slightly rounded—as is the case with most larger V tools, then the outside shape must be rounded to match. A protruding tip at the bottom of the V indicates the outside grinding does not match the inside shape of the tool. An indentation on the side near the bottom indicates that the outside grinding is not parallel to the inside plane of the tool.

The Wire Edge

When grinding the edge of a tool, most of the steel turns into filings. When the steel is very fine, instead of being ground away it bends away from the stone. This is called the burr or the wire edge. The presence of a wire edge indicates that you have ground past the previous edge. This is the signal that most carvers use to indicate that they have ground enough steel away. In the proper light you can see the wire edge, and you can also feel it if you pull your finger across the surface opposite the side you were grinding on. The wire edge is removed by running a slip stone on the inside of the tool (see Fig. 7). A variety of shapes are available to match the shape of the tools. You can also remove the wire edge with a piece of hardwood cut to the inside shape of your tool. Put a little honing compound on it and draw it parallel to the inside surfacc.

Many sharpening machines have cloth wheels that are used to remove the wire edge (see Fig. 8). Because they are flexible, they shape themselves to the tool. Caution: also because the cloth wheel is flexible it wraps itself around the edge. Too much polishing on the cloth wheel will round the bevel, which changes the cutting angle of the tool. If you use a machine, use the cloth wheel very judiciously.

Final Honing

After the tool is ground to shape, it must be polished. This cuts down resistance and removes any remnant of a burr. This is usually done on a strop, or a wheel of leather or rubber composition. Usually the strop is loaded with honing powder or paste. Pull the tool along the strop, the cutting edge following. Take care to keep the bevel flat on the strop so that it is not inadvertently rounded either at the heel or the tip.

Like the barber who strops the razor before and during a shave, wood carvers strop their tools often. Experienced carvers are usually able to keep a tool in service for a long time—often years without having to regrind them. They use their tools carefully, keep them stropped, and the edge lasts a very long time, (inexperienced carvers who twist and pry with their tools—and often "cheat up" while honing their tools—have to regrind them often.)

Test the sharpness of your tools by cutting cross grain in soft wood. If the wood shines under the cut, the tool is sharp. If the cut is fuzzy, keep working on it. The proper bevel is on the tool if, held in the traditional two-handed posture, the tool cuts immediately upon touching the wood.

Sharpening is a learnable skill. A surprising number of beginning carvers arc impatient when it comes lo learning to sharpen. They want lo "gel carving" and consider the time spent sharpening as a delay. I encourage new carvers, instead, to take pride in the sharpness of their tools—to embrace the art of sharpening with the same energy that they have for carving itself. You'll never become a "master carver" without first becoming a "master sharpener"!

40 • Creative Woodworks S. Crafts August 2001