An engine lathe (Fig. 198) is the commonest form of this type of machine and is used mostly for turning straight pieces. It is constructed to support a spindle which is free to revolve through the medium of stepped-cone pulleys and belts. The spindle is supported by the head-stock, which is fastened to the bed which rests on legs of convenient height. The work is revolved or driven by centers, face plates, or chucks. The chucks are fastened to the spindle. If the casting or metal requires a support at both ends, the tail-stock with an adjustable center is used and is operated by a hand-wheel. When used for turning, a tee rest is employed to support and assist in guiding the tools. Cylindrical or round work is held between centers, and the tool is gripped in a tool post, which in turn is part of the carriage. The carriage is advanced by means of a screw feed, or through gears driven by means of a feed rod.