Fig. 2760.
Obviously the fleam makes the points weak, but this in coarse saws may be partially remedied by shaping the teeth as in [Fig. 2760]. Fleam on the front face or throat of the tooth has the effect of preserving its set, the pressure of the cut being as shown by the arrows in [Fig. 2753].
It is evident that the finer the point of the tooth the sooner it will become dulled, and that the harder the timber the more quickly the tooth will become dull. So soon as this occurs the teeth refuse to cut freely, and the extra pressure on them acts to spring them upward and to take off the set. It is obvious that for soft wood the teeth may be given fleam on both faces, and that the front face should have some fleam, even for the hardest of wood, whether the back face has fleam or not. Also, that in proportion as the grain of the wood runs more across the saw kerf than in line with it the teeth should be filed to cut on the side, and the hook of the front face may be lessened, while vice-versâ, in proportion as the grain of the wood runs parallel with the kerf, the tooth may have hook and fleam on the back face with a slight fleam on the front one.
Fig. 2761.
Gauges.—Of gauges for marking on the work lines parallel to its edges there are several kinds, a common form being represented in [Fig. 2761], in which the block that slides against the edge of the work is secured by a set-screw.
A better method, however, is to use a key set at a right angle to the stem, so that the head may be tightened or loosened by striking it, as if it were a hammer, against anything that may happen to lie on the bench, hence the gauge may be set and adjusted with one hand while the other is holding the work, as is often necessary when marking small work. The marking point should be a piece of steel wire fitted tightly in the stem, the protruding part being ground or tiled to a wedge, with the two facets slightly rounding, and whose broad faces stand at a right angle to the stem of the gauge, the point or edge only projecting sufficiently to produce a line clear enough to work by; otherwise it will not be suitable for accurate work.