Edmund S. Smith

For the benefit of amateur workers who have found difficulty in keeping a good sharp edge on plane irons, chisels, etc., a device is described below which, if properly made and used, will eliminate the main source of this trouble.

In sharpening a plane iron, for example, on an oil stone the chief difficulty lies in maintaining the tool at a constant angle with the stone on the forward and backward strokes. Any change in this angle of course produces a more or less rounded bevel on the iron as shown in exaggerated form in Fig. 1. When this rounding is at all marked it is next to impossible to secure a sharp working edge. As the degree of rounding of the bevel becomes less, the ease and rapidity with which a fine edge may be obtained materially increases.

Jig For Sharpening Tools On An Oil Stone 283

Fig. 2.

The desideratum, therefore, is to secure an absolutely flat bevel. To this end the writer devised the holder shown in the drawings, and found that it worked so satisfactorily that it is now offered to any one who may have encountered the difficulty he found in keeping the tool at a constant angle with the oil stone. By its use a tool may not only be ground more perfectly, but even with the extra time required in clamping the tool in the holder an actual saving of time is effected, especially if considerable stock is to be removed as in grinding out nicks, etc.

The device consists of the cylindrical steel bar A, recessed along its central portion to receive the flat piece of steel C, which is clamped to it by the thumbscrews D, D. The rounded rods B, B slide through the bar A near its ends at an angle of about 70 degrees with the flattened portion of the bar. Their position with regard to A is adjustable by means of the knurled screws E, E.

In use, the tool to be ground, a plane iron for example, is clamped between A and C and the legs B, B so adjusted that the iron meets the oil stone at the desired angle, as shown in Fig. 3. For the commoner angles the tool is clamped about four inches from its edge. The legs rest upon the bench (or other plane surface) straddling the stone. The tool and its holder are now moved back and forth over the stone as usual, the resulting bevel being of course perfectly flat.

By adjusting one of the legs so that it is longer than the other edge will be ground at an angle with the side of the tool instead of square with it. This same result is obtained by clamping the tool at any other than a right angle with the bar A. In this way the edge of the tool may be more or less rounded if so desired or it may be ground straight, but at an angle of as much as 45 degrees with the side of the tool. The degree of the bevel is determined by the length of the legs B B extending through A, ad also by the distance the tool is clamped from its edge in the holder. When the bevel is ground the tool and holder are turned over and the flat side of the tool rubbed on the stone to remove the burr, the holder in no way intrfering with its movment.

Jig For Sharpening Tools On An Oil Stone 284

Fig. 3. FIG. 1.

The most convenient oil stone to use is the so-called "combination stone" made of carborundum or other abrasive, consisting of a coarse and a fine stone cemented face to face. The coarse side is used on very dull tools where considerable stock has to be removed. When this is accomplished the stone is simply turned over and the fine side will soon put a keen edge on the tool.

The size of the holder depends partially upon the kind of tool to be used in it, but the dimensions of the parts given below will be found convenient for a holder to include chisels and plane irons up to 2 1/2 in. wide.

Bar A, 5 1/2 in. long, 3/4 in. diameter.

Rods BB, 3 1/2 in. long, 3/8 in. diameter.

Bar C, 3 1/2 in. long. 3/4 in. wide, 1/4 in. thick.

All four screws 1/4 in.