What is it?

A full description of stone hammer drilling can be found on the excellent akvopedia website and within the Practica drillling manual and maufacturing manual. It is designed to be used in conjunction with Rota Sludge Drilling with the hole full of drilling fluid. When a hard layer is found the stone hammer is attached and a cable run through the rota sludge drilling pipes. The hammer slides inside the drill bit and therefore can fall much faster than if it was just in the drilling fluid, which would slow it a lot.