Abstract: A device for applying cavitating liquid jets to a work surface has an annular work surface engaging area surrounding a chamber, recessed into the device and with an open end adjacent the working surface, a jet nozzle on the opposite side of the chamber which projects a high velocity liquid jet against the working surface, and passages extending from the chamber to the interior of the tool and providing the main route for escape of spent liquid, the passages being calibrated so as to maintain the chamber full of liquid without engendering a substantial pressure rise within the chamber. The velocity of the liquid jet is high enough that shear between the jet and the spent liquid causes cavitation.