by J.M.Drew St. Paul Publishing Company 1918
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Sharpening a Saw
This order should be followed in sharpening all saws, whether cross-cut or rip saws; the top-jointing, setting and side-jointing being the same in all; the only difference being in the filing. In filing any saw where a three cornered file is used, we file one side each of two teeth at once. If you find that one tooth is getting sharp before the other, bear harder against the large or duller tooth, but be careful to keep the pitch or angle of the tooth the same. When starting to file notice carefully the position of your file: First, in regard to the angle across the saw as in A Figs 4 and 5. For a rip saw the file should be about square across; for a cross-cut, an angle of about 45 degrees.
Second. Notice the pitch of the tooth as at B Fig. 6. Be very careful as you proceed that the file does not turn in your hand or handle and change the pitch as at B in Fig. 6. Third. The bevel or level of the file, whether the handle of the file be up or down. Be careful to notice these points in starting and then keep them the same throughout the filing. If these positions change, the teeth will be of different shapes, as at E. If a tooth be broken out, do not file the broken part, but keep the teeth on each side their original size, and the broken one will "grow" longer each time the saw is filed until it finally becomes of full size or length. The rip saw, which is used for ripping or splitting timber is usually filed square across; the action of the teeth being similar to that of a row of small chisels, each tooth being a chisel. Fig. 7 shows the shape of the teeth in the rip saw, filed square across. The front side of the teeth should be kept at right angles to the line of the cutting edge of the saw. For ripping hard or cross-grained wood it is well to give the teeth a little bevel by lowering the handle of the file a trifle, also to let the teeth start back slightly, so as not to bite too freely; but for clear pine, straight across, and at right angles to the length of the blade is better. In filing the rip saw it is best to file against the cutting edge of the teeth, filing one-half the teeth from each side.
The cross-cut saw is filed in quite a different manner from the rip saw. As it must cut the grain or fiber of the wood in two places, one on each side of the saw, it must also break and carry out the chips or dust between the two cuts. Let Fig. 8 represent the end view of a saw cutting a piece of timber; A being the saw, B the timber. C shows the point which does the cutting and D the part of the tooth which breaks and carries out the chip or sawdust. For cutting soft wood, the point D may be longer and sharper than for cutting hard wood, as the saw dust is more easily broken out. In cutting hardwood the point should be more blunt, in order to break out the dust as soon as it is cut by the points. The length or bluntness of these points is regulated by the level of the file across the saw. Holding the file level will make the point long, while lowering the handle of the file will make the point blunt-providing the file be kept out an angle of 45 degrees to the length of the saw in each case.
In filing the cross-cut saw it is best to run the file at an angle of 45 degrees across the saw as this gives the best results; sharpening the front of the tooth so as to cut both smooth and fast. Fig. 5 shows the plan, or the appearance on looking down at the saw and file from the top. The file should be held at about this angle in filing nearly all cross-cut saws.
The pitch of the teeth is an important feature. Too much pitch is a common fault. It is well to have a little, but too much pitch will make a saw cut rough and push hard. Fig. 6 B shows a saw with no pitch at all, and the bevel the same on each side of the tooth. The file is held level in filing teeth in this shape which issued largely in cutting 80ft wood-principally in the buck saw.
Fig. 9 shows a saw with the same amount of bevel on the face of the tooth and none on the back. This form is used in the buck saw for cutting hard wood. To make teeth of this shape, lower the handle of the file, but keep it at the same angle (45 degrees), across the saw. In filing the cross cut saw the file should be held so as to file from the handle towards the point of the saw. Some filers claim that this will cause a rough or wire edge on the face of the tooth. This may be true but such edge will be removed when the saw is side jointed. No saw, even though the teeth are not set, should ever be filed wholly from one side, as the file turns a slight edge which increases the set. This should be distributed to both sides of the blade by filing half the teeth from each side.
Table showing the different sizes of drills that should be used when a full thread is to be tapped in a hole. The sizes given are practically correct.