GB190513855A - Improvements in or connected with Screw Jacks - Google Patents

Abstract

13,855. Lake, W. B., and Elliot, E. F. July 5. Lifting-jacks of the type in which a screw is operated by double-acting pawl-and-ratchet mechanism are provided with means for preventing the engagement of the idle pawl with the ratchetwheel, and also with means for roughly adjusting the screw to the height of the work. Figs. 4 and 5 show the lifting-jack, with the buttress threaded screw B, engaged by a coned nut F constructed in three or more sections. The nut F is in frictional contact with the inner coned surface of a hollow ratchet-wheel C having a ring of double teeth c at the upper portion of its periphery, and an annular groove c<2> in the lower portion which is engaged by a spring-pressed ball c<3>, secured in a recess in the casing A by the stud a<6>. A peg c<6> working in a slot on the nut F is used also to connect the nut and the cap c<4> of the ratchet-wheel. The ratchetwheel C also has a flange fitting on the shoulder a<1> of the standard, and is operated by a double pawl D, pivoted at d<2> to a pair of plates d<4> loosely mounted on the standard A. A spring guard-ring E, having its ends e bent outwardly, surrounds the ratchet-wheel, and by moving the handle d<8>, the pawl D, and the plates d<4> bodily round the standard, the central projection d<5> on the pawl can be made to engage one of the ends of the loose guardring and move it through a sufficient angle to allow either of the pawls to engage the ratchetwheel. The other pawl is prevented from engaging the wheel by the guard-ring. When pressure is applied to the screw in an upward direction, the inclined screw-surfaces force apart the sections of the split nut and allow the screw to be rapidly raised. To lower the screw rapidly, the jack is inverted, and the split nut then falls upon the coned cap c<4> of the ratchet-wheel, thereby forcing the sections apart and permitting the screw to be pushed into the casing. Other methods of connecting the nut and ratchet-wheel may be used ; for example, flat roughened surfaces may be provided on each, or the nut may be omitted and the inner surface of the ratchet-wheel provided with a screw-thread engaging the lifting-screw.