APPARATUS TO CONTROL GRAVITATIONAL MOVEMENT OF A GEM STONE POLISHING TANG TOWARDS A STONE POLISHING SURFACE

摘要

A dashpot 6 for controlling the gravitational movement of, for example, an arm 1 in a gem polishing machine is connected by a flexible tube 7 to an upstanding tube 8 which is movable vertically to adjust the position of balance of the dashpot plunger 5. The tube 8 is raised or lowered by a motor 9 controlled by movements of the arm. When the arm is lowered, a follower 4 on the arm engages the plunger 5 before the gem held by a dop or chuck 2 engages a polishing wheel 3. The weight of the arm gradually depresses the plunger as the gem is polished. If the arm is light or counter-weighted, its pressure on the plunger may be insufficient to move it sufficiently from its initial balanced position this difficulty is overcome by the automatic lowering of the tube 8 so that liquid (e.g. mercury) flows out of the dashpot. After polishing, the arm is lifted off the wheel and dashpot, the tube being quickly restored to its original position causing liquid to flow back into the dashpot. A restriction valve 12 in the tube permits the liquid to flow more rapidly into, than out of, the dashpot.