Fig. 41, B. Cutting-off Saw.
Fig. 41, C. Compass, or Keyhole, Saw.
Fig. 41.—Saws.
(In each of the three varieties of saw teeth shown in
Fig. 41, the set of the teeth is exaggerated.)
In all except the finest saws, the teeth are set; that is, the points are bent a very little in such a way as to make the cut wider than the thickness of the blade, so that the saw may cut through the wood without binding, which it could not do if the cut were the same thickness as the blade. The blades of all high grade saws are thinner upon the back than upon the cutting edge, but if the saw is to be used upon the finest work, this difference in the thickness of the two edges of the blade is supposed to make the setting of the saw unnecessary. For general work, it will be found that the saw will be much more efficient if it is given a set adapted to the size of the teeth, or to the nature of the work it is expected to do.
The compass, or keyhole, saw (Fig. 41, C) is used where it is necessary that the saw should cut both with and across the grain. It is used to start the cut for a rip- or cutting-off saw, when a cut has to be made in the surface of a board. This saw is used also in many places where it is not practicable to use a larger saw, and for sawing curves. In order to allow it to cut around curves easily, the face, or cutting edge, is considerably thicker than the back, and the blade is made of soft metal. It may then be given a heavy set, so that it will bend instead of breaking or kinking, as it would be liable to do from the nature of its work if made of tempered steel.
Some carpenters working upon job work, where it is desirable to carry as few tools as possible, have a narrow 20” or 22” saw sharpened like a compass saw, which for ordinary work is quite satisfactory as either a cutting-off or a ripsaw, thus making another saw unnecessary.
Fig. 42.—Backsaw.