Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 84

A saw must in one dimension (that of thickness of blade at least) be very thin, and that part cannot be strengthened by means of ribs. When a strengthening bar is introduced at the back as in tenon saws (see Fig. 244, p. 66), the depth of cut is limited. If a light saw blade be pressed against an object or hooked on one, then tension causes this straight blade to be more and more strengthened. On the other hand, if the saw blade be pressed forward by thrust, the weakness of the blade is apparent from the bending. Now, formed as saw teeth are, either to cut in both directions or in the forward direction only, there is always one direction in which the work to be done is accomplished by a thrust upon this thin metal. Clearly the metal will bend. If, however, the teeth cut in the direction of tension only, the work tends to preserve the straightness of blade, and upon this an important quality and use of the tool depend. That this tension system can be efficient with a very narrow blade is clear from the extensive use of band saws. There is, however, a property in the breadth of the blade which applies equally to the tension and thrust systems—it is the guide principle. The breadth of the blade operates by touching the sides of the gateway opened by the teeth. When it is desired to dispense with a straight guide for sawing purposes, it is done by narrowing the blade as in lock saws, keyhole saws, tension frame saws, etc.

Fig. 222.—Hand Saw Handle.

Fig. 223.—Three Rip Saw Teeth Points to Inch.

Fig. 224.—Three and a half Rip Saw Teeth Points to Inch.

Fig. 225.—Four Rip Saw Teeth Points to Inch.

Fig. 226.—Four and a half Rip Saw Teeth Points to Inch.