An overburden drilling device includes a drill bit body, a percussion element for applying impacts to the body, and a casing attached to the body. The casing is connected to the drill bit body by a casing shoe which comprises semi-cylindrical halves which are held together by a circular ring that...http://www.google.de/patents/US5839519?utm_source=gb-gplus-sharePatent US5839519 - Methods and apparatus for attaching a casing to a drill bit in overburden drilling equipment 
