Fig. 917.
The principal forms of cutting tools for lathes are the diamond points or front tools, the side tools (right and left), and the cutting off or parting tool. The cutting edges of lathe tools are formed by grinding the upper surface, as a in [Fig. 916], and the bottom or side faces as b, so that the cutting edges c and d shall be brought to a clean and sharp edge, the figure representing a common form of front tool. The manner in which this tool is used to cut is shown in [Fig. 917], in which the work is supposed to be revolved between the lathe centres in the manner already described with reference to [driving work in the lathe]. The tool is firmly held in the tool post or tool clamp, as the case may be, and is fed into the work by the cross-feed screw taking a cut to reduce the work diameter and make it cylindrically true; the depth to which the tool enters the work is the depth of the cut. The tool is traversed, or fed, or moved parallel to the work axis, and the motion in that is termed the feed, or feed traverse.
Fig. 918.
The cutting action of the tool depends upon the angles one to the other of faces b, d ([Fig. 918]), and the position in which they are presented to the work, and in discussing these elements the face d will be termed the top face, and its inclination or angle above an horizontal line, or in the direction of the arrow in [Fig. 918], will be termed the rake, this angle being considered with relation to the top a a, or what is the same thing, the bottom e e of the tool steel. The angle of the bottom face b to the line c is the bottom rake, or more properly, the clearance.
Fig. 919.