59.—Screw Press.details

A lever and an inclined plane may be combined together into a screw-press, the incluned plane being coiled up into a spiral or screw-thread (fig. 59). For every complete revolution of the lever, the weight is raised a distance equal to that between the spires of the screw-threads; hence the mechanical advantage of such a press is the circumference of the circle traversed by the force applie dat right angles to the lever, divided by the distance between succes­sive spires of the screw. Wheels and axles are usually combined by means of cogs, as is well seen in the wheel-work of a clock. (p. 138)