Excessively heavy cuts may be taken by the form of tool shown in [Fig. 1808], in which a is the tool, b the tool box, and c the work, the depth of cut being from d to e, which may be made 21⁄3 inches if necessary. The face f of the tool is ground at an angle in the direction of i, so that the tool shall take its cut gradually, and that the whole length of the tool cutting edge shall not strike the cut at the same instant, which would cause a sudden strain liable to break either the tool or some part of the machine itself. So likewise the tool will leave its cut gradually and not with a jump. As shown in the cut, but a small part of the cutting edge would first meet the work, exerting for an instant of time only enough pressure and resistance to bring all the working parts of the machine up to a bearing, and as the tool descends (as denoted by the arrow g), the strain would increase until the whole length of tool cutting edge was in operation. For such heavy duty as this the tool is tempered down to a purple to give it strength.
Chapter XXI.—THREAD CUTTING.—BROACHING PRESS.
In [Fig. 1809] is represented a front view of a patent die stock for threading pipe up to six inches in diameter. In the figure the three bits or chasers are shown locked in position by the face plate, which is shown removed in [Fig. 1810]. [Fig. 1811] shows the machine with the face plate removed, the bit or chasers having pins in them which fit into the slots in the face plate, so that by rotating the plate the chasers may be set to size.
Fig. 1809.
