Electrically driven fastening appliance

A power fastening tool comprising a housing closed at one end, a tool driving spindle journalled at said closed end and extending outwardly therefrom, an electric motor mounted in said housing and having the drive shaft extending therefrom and an automatic clutch control planetary gear system interconnecting said motor drive shaft and said spindle, said gear system comprising a central gear fixed to said motor drive shaft, a plurality of planetary gears arranged around said central gear supported on a planet carrier connected to said spindle and drivable by said central gear and an annulus member having an internal gear which coacts with the planetary gears for revolution about the central gear, said annulus member having one end closed to form a face in opposition to the closed end of said housing, said annulus face and said closed end being provided with resiliently engagable clutch means operating to respectively maintain said annulus member stationary relative to said housing on application of a first torque not exceeding a predetermined level and to permit rotation of said annulus member with respect to said housing on application of a second torque greater than said predetermined level.