Fig. 980.
Fig. 981.
Fig. 982.
It is obvious that a Whitworth thread might be cut with a single-pointed tool such as shown in [Fig. 980], the corner at b being rounded to cut the rounded tops of the thread. It is more usual, however, to employ a chaser set in the tool point in the same manner as a single-pointed tool, or in a holder fixed in the tool post. When a single-pointed tool is employed to cut a thread, the angles of its sides are not the same as the angle of the thread it produces, which occurs because the tool must have clearance to enable it to cut. In [Fig. 981], for example, is a single-pointed tool without any clearance, and, as a result, it cannot enter the work to cut it. In [Fig. 982] the tool is shown with clearance, and, as a result, the angle of the cutting edge is not the same angle as the sides of the tool are, because the top face is not at a right angle to the sides of the tool. It is obvious that the angle of the sides of the tool must be taken along the dotted line in [Fig. 982].
