The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking. Paul N. Hasluck
long enough to reach the tooth from the table, place a parallel block of wood on the table, and put the rule on it, or draw a line on the plate, and place the rule on the plate in a line with this line. This test applies to all hand saws mentioned in this chapter. Fig. 282 shows how to find the angle of a saw-tooth; B is the rule, C is the saw-tooth at an angle of about 65°, and D is the line on the saw-plate, or on the top of the saw-table, as the case may be.
Fig. 281.—Protractor.
Fig. 282.—Ascertaining Angle of Saw Teeth.
Figs. 283 and 284.—Unevenly Worn Teeth.
BEGINNING HAND SAW SHARPENING.
Before attempting to set and sharpen saws for actual work, the beginner should practise on an old saw or on a piece of saw blade which he cannot possibly spoil. If such a vice as shown by Figs. 267 and 268, p. 71, is used, fix the bottom of it A in the bench-vice, and then place the saw between its jaws with the teeth standing about 1/2 in. above. If the saw is placed further out of the block, the action of filing will cause it to vibrate, and very soon the teeth will be stripped off the file. The teeth of an old saw will probably appear as in Figs. 283 and 284, that is to say, the teeth will be uneven and some may be longer than others. With the saw in this condition only some of the teeth can be at work, therefore they all must be brought to one common level. To accomplish this the flat file (Fig. 280, p. 73) is passed down the saw’s edge, or top of teeth, two or three times in succession, in the manner shown at Figs. 285 and 286, the former being an end view, and the latter a front view. It may now be seen by looking down the edge, as shown in Fig. 286, whether all are level. If the tooth points are not in line, those which are below the rest will not work. Hence, in sharpening, as in setting, perfect uniformity is essential to the best results. This process of filing down the teeth is called topping.
Figs. 285 and 286.—Topping Saw Teeth.
Fig. 287.—Filing Saw Teeth.
SHARPENING HAND SAWS.
The teeth at both point and butt of a hand saw should be very slightly smaller than those in the middle, as it is at the last-named point where the greatest force is exerted in every down stroke. But it is absolutely necessary that the set is the same from point to butt of every saw, whether rip or cross-cut. The middle of the cutting edge of a cross-cut saw should be slightly rounded, being highest at about the middle. The saw being still in the saw vice, insert the file in a handle, and grasp it with the right hand, taking the point of file in the left, as shown in Fig. 287. Place the file against the face of that tooth nearest the handle that inclines away from the worker, holding the file at an angle with the blade of saw as shown in Fig. 287. Then lower the right hand to about the angle shown in Fig. 288 (which shows the left hand removed). The file should be held obliquely across the saw blade, as in Figs. 289 and 290, the point end of the file being inclined towards the saw handle as illustrated by Fig. 287. Gently push the file forwards, lifting it at the end of stroke, returning it, and again pushing it, until the point of the tooth has a keen edge. Repeat this upon each alternate tooth until all upon one side are sharpened. Afterwards turn the saw in its vice and sharpen the teeth upon the other side in the same manner. Be careful not to press the file against the back of the tooth, or unevenness will surely result. It may occasionally happen that when touched with the file, the saw may be found to be too hard. To soften it, remove the handle, and “blaze” by smearing the blade with a mixture of wax, suet, and oil, and heating over a fire till the mixture ignites. But this is not a method for the beginner, who would certainly spoil the saw. Keep all saws slightly rounding on the edge. The rip saw and hand saw can have a quarter of an inch rounding with advantage. To do this the points of the teeth must be frequently filed down, and the heel and the point filed away. There are always several teeth at the heel and at the point that do little work; those in the middle portion do most, and consequently wear away fastest. All saws, except circulars, have a constant tendency to get hollow, and this must be prevented; and the only way to prevent it is to file the teeth down by passing a partly-worn file along the edges, till it touches every tooth. Then, in filing the teeth, take care only just to take out this bright mark—not one touch more, or that tooth gets low and does not work; if some teeth are filed away even a little too much, the saw might just as well be that number of teeth fewer, as they do no work. A saw in thoroughly good order is so sharpened that each tooth does a share, and no one tooth more than the others.
Fig. 288.—Filing Saw Teeth.
Fig. 289.—Filing Saw Teeth.
Fig. 290.—Filing Saw Teeth.
Fig. 291.—Badly Sharpened Tenon Saw Teeth.
SHARPENING TENON SAWS.
Sharpening tenon saws is practically the same as sharpening hand saws. It may happen, however, that some of the teeth will be much larger than others, this being due to the file not having been held at the same angle in sharpening each tooth. Fig. 291 shows the saw teeth improperly sharpened, the front of the large teeth inclining much more than the front of the small teeth. If the teeth on one range are found to be filed smaller than those on the other, file the back of the smaller teeth to a more acute angle, keeping the file at the same time well against the front of the other tooth at the bottom; and see, before the filing is finished, that the front of the next tooth has been filed up to its point, as it is the front, not the back, of the tooth that does the cutting. To regulate the teeth of the saw, file every tooth in succession, shooting the file straight across the teeth. After filing all the teeth from one side, turn the saw and file