Movement No. 151 converts continuous circular motion into continuous but greatly reduced rectilinear motion, using a worm gear driving a dual-threaded screw shaft. A worm on the upper shaft meshes with a toothed wheel fixed on the screw-shaft, providing a large speed reduction. The screw-shaft itself is cut with two threads: a right-hand thread on one section and a left-hand thread on the other. Two nuts are threaded onto these opposite sections — one on the right-hand thread and one on the left-hand thread. As the screw-shaft rotates, both nuts travel simultaneously, but in opposite directions — they move toward each other when the shaft turns one way, and away from each other when it turns the other way. The worm gear reduction means the nuts move very slowly relative to the input rotation, providing precise and powerful clamping or spreading force. This mechanism is widely used in vises, clamps, and centering devices where symmetric, simultaneous closing or opening of two jaws is required.
151. Continuous circular into continuous but much slower rectilinear motion. The worm on the upper shaft, acting on the toothed wheel on the screw-shaft, causes the right and left hand screw-threads to move the nuts, upon them toward or from each other according to the direction of rotation.