Fig. 971.
On small work the edge a a should be ground straight, and set at a right angle to the work, so that it may face off the whole surface at once, but for work of large diameter it should be ground and set as in [Figs. 970] and [971], so that it will cut deepest at the end e, enabling it to carry a finishing cut from the circumference to the centre, by feeding it with the cross-feed screw.
Fig. 972.
Fig. 973.
The cutting edge should be level with the centre of the work, the angle of the top face d being about 35 degrees in the direction of the arrow c for wrought iron, and level if used for brass. When this tool is to be used for a face close to the work driver it should be bent at an angle as in [Fig. 972], so as to enable the driver to clear the slide rest, and when used for countersunk head bolts, it may be bent at an angle as in [Fig. 973], so that when it is once set to give the head the correct degree of taper, it will turn successive heads to the correct taper without requiring each head to be fitted to its place.