Vacuum chuck

Claim 1

A vacuum chuck for use in lens grinding comprising a cylindrical block with a concave upper surface having on its outer edge an annular gasket whose outer diameter is equal to the diameter of the block; said block being provided with a vertical circular bore extending downward from the top of the block to join a through horizontal passageway in the block, the vertical bore being constricted before joining the through horizontal passageway; said vertical bore having resting therein a helical spring and a metallic sphere on top of the spring, the diameter of the sphere being less than the diameter of the bore, and an annular groove below the top opening of the bore, said groove holding an O-ring whose inner diameter is less than the diameter of the sphere; the through horizontal passageway having two opposed openings, one side of said passageway being constricted towards the center of the block to form a venturi which meets the bottom opening of the vertical bore, and the other side of the passageway being widened beyond the venturi; and a separate L-shaped passageway comprising a horizontal portion going inward from the side of the block to join a vertical portion going downward from the top of the block, the horizontal portion being threaded and holding a screw cap.