Читать книгу The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking - Paul N. Hasluck - Страница 85

In thrust saws the hand and arm of the workman occupy a definite position, and the line of pressure on the saw is thus very much determined by the inclination of the handle to the line of teeth prolonged backwards. If the handle be placed at such an angle that a large part of the resolved thrust be perpendicular to the line of teeth, then the bite may be greater than the other resolved portion of the power can overcome. At another angle the bite may be very little, and although the saw thus constructed would move easily it would work sweetly, but slowly. The construction is suitable for saws with fine teeth and for clear cuttings. With regard to single-handed saws only, whatever may be the other conditions required, most handles have curved hook projections, shown in Figs. 217 to 224, p. 61, which show a variety of shapes in hand saw handles. These projections are connected with the pressure of the sawyer on the teeth. If, in sawing, the hand bears upon the upper hook, then an increased pressure is given to the forward teeth; if upon the lower hook the pressure on the saw teeth is released, and there is consequent ease in sawing. The angle at which direct thrust ought to act upon the line of teeth in the saws is obviously very different. Each material may be said to have its own proper angle, and in some saws provision is made by two set screws opposite the hooks for varying the intersection of the line of thrust with the line of teeth. In the biggest one-man saw used in handicraft—a tool quite 4 ft. long—the upper hook of the handle is wanting (see Fig. 222), because under any circumstances the weight of the saw is more than sufficient, and therefore it is not requisite that any resolved portion of the workman’s energy should be compounded with this But the lower hook must be retained, that the weight of the saw may be taken from the work. For these reasons the line of direct thrust is nearly parallel with that of the teeth. There appears to be much inconsistency in the placing as well as in the formation of saw handles, and this is the case particularly with saws for cutting metal.

Fig. 227.—Five Rip Saw teeth Points to Inch.

Fig. 228.—Five and a half Rip Saw Teeth Points to Inch.

Fig. 229.—Twelve Cross-cut Saw Teeth Points to Inch.

Fig. 230.—Eleven Cross-cut Saw Teeth Points to Inch.

Fig. 231.—Ten Cross-cut Saw Teeth Points to Inch.

Fig. 232.—Nine Cross-cut Saw Teeth Points to Inch.

Fig. 233.—Eight Cross-cut Saw Teeth Points to Inch.

Fig. 234.—Seven Cross-cut Saw Teeth Points to Inch.

Fig. 235.—Six Cross-cut Saw Teeth Points to Inch.

Fig. 236.—Five Cross-cut Saw Teeth Points to Inch.

Fig. 237.—Four Cross-cut Saw Teeth Points to Inch.