Winch Crab Single
Winch Crab Single:
The crab and winch handle in its simplest form is a simple application of the mechanical principle of the wheel and axle, the handle representing the wheel and the crab or drum the axle. It is used for raising small loads of earth, etc., from deep excavations, and consists of two upright posts, a round wooden drum, through the centre of which an iron rod is passed, this being cranked at one end to form the winch handle, and two iron straps bent into shape to form bearings in which the iron rod can be made to revolve.
But few hoisting machines are so simple as to comprise only the winch handle and drum. The power gained would be totally insufficient for lifting heavy loads. In the single-purchase crab (Fig. 227) the first advance on this device occurs. The winch handle is not put on the same shaft as the drum, but on another lying parallel to it, and the two shafts are geared together by means of toothed wheels, a small one actuated by the winch handle directly actuating a large one on the same shaft as the drum.