Fig. 1319.
Screw Cutting with Hand Tools.—Screw threads are cut by hand in the lathe with chasers, of which there are two kinds, the outside and the inside chaser. In [Fig. 1319] is shown an outside, or male, and in [Fig. 1318] an inside, or female chaser. The width of a chaser should be sufficient to give at least four teeth, and for the finer thread pitches it is better to have six or eight teeth, the number increasing as the pitch is finer, and the length of the work will permit. The leading tooth should be a full one, or otherwise it will break off, and if in cutting up the chaser a half or less than a full tooth is formed it should be ground off. The tooth points should not be in a plane at a right angle to the chaser length, but slightly diagonal thereto, as in [Fig. 1319], so that the front edge of the chaser will clear a bolt head or shoulder, and permit the leading tooth to pass clear up to the head without fear of the front edge of the steel meeting the shoulder.
Fig. 1320.
Fig. 1321.