Woodworker's Journal 1985-9-2, страница 18

The Beginning Woodworker

Sharpening Plane Blades and Chisels

In any discussion of woodworking,

every individual has his own ideas and opinions. There is one element of woodworking however, that woodworkers universally agree on: The absolute necessity for sharp cutting tools. Yes, there are various sharpening devices and procedures, but one fact remains crystal clear: Sharp tools are the key to safe, successful woodworking. Dull tools will not only make for difficult, rough looking work; they are dangerous. The extra effort required to force a dull tool through the material is frequently the cause of serious accidents.

Because the proper care and sharpening of cutting tools is so important to quality woodworking, the novice is urged to master this phase of the craft as soon as possible after a basic tool collection is acquired. Indeed, many tools when purchased do not have a final cutting edge applied. It is therefore imperative that the beginning woodworker understand the principles and master the technique of sharpening even before he begins "working" the wood.

There are many types of cutting tools, however we will confine the present discussion to beveled cutting edges, such as those found on plane irons and chisels. These require frequent maintenance if they are to be used with maximum efficiency.

There are four basic steps involved in establishing a keen, effective cutting edge on bevel-edged tools. First, the cutting edge must be ground free of nicks and square to the sides. Second, the bevel must be ground to the correct angle. The third step involves whetting or smoothing of the edge to remove roughness caused by grinding, and to further refine the cutting edge. It is at this stage that a slight secondary bevel may be added to plane irons and chisel blades that will be used in hardwoods. The fourth and final step is to hone or polish the edge with a leather strop or on a buffing wheel. This last step will result in the cleanest, sharpest, most effective cutting edge possible on a hand tool.

The first two steps will not always be

necessary, however. Grinding is only required when the edge has been nicked or chipped, or when continued whetting has reduced the length of the bevel to a point when a new bevel must be established.

Determining the correct bevel angle is important. In theory the smaller the angle the sharper the blade will be. Witness, for instance, the common razor blade. In practice however, there is a world of difference between shaving whiskers and cutting hard maple. An ultra-sharp edge with a narrow bevel will quickly chip and break in hardwoods. The greater the bevel angle, the less chance there is of this occur-ing. The ideal bevel angle, therefore, is a compromise between sharpness and durability. Most experts agree that the primary bevel angle for plane and chisel blades should be about 25 degrees (Fig. 1).

The first step in sharpening is to grind away any nicks or imperfections in the edge while simultaneously es-stablishing a right angle. As shown in Figure 2, the blade should be checked with a try square to make sure that the edge is indeed square to the sides.

are ground perfectly square, jack-planes are usually given slightly curved edges (Fig. 3A). The purpose of this is to facilitate the removal of large amounts of material without

gouging or tearing out at the blade sides. The surface is then finished flat with a smoothing or bench plane (Fig. 3B).

Next, the bevel must be ground uniformly across the width of the blade. Although the recommended bevel angle is 25 degrees, this figure can be adjusted several degrees in either direction depending on the relative hardness of the wood being worked. A keen 22 degree bevel will slice cleanly through soft pine, but will tend to chip in oak, where a bevel angle approaching 28 degrees is better. However, for most general purpose work it is best to maintain the standard 25 degree bevel angle.

There are several methods to either grind an edge or produce a bevel. Using a coarse oilstone and old-fashioned elbow grease is a slow and tedious process, and it produces a flat bevel. A power driven grinding wheel is far more efficient and, because of the circular grinding wheel, a hollow ground bevel will result. The difference between flat and hollow ground bevels is shown in Figure 4.