A blade clamp assembly for retaining a rotary blade on the arbor of a rotary tool comprises a blade washer for engaging the blade to hold the blade on the arbor and a clamp assembly threaded into the arbor to clamp the blade washer against the blade. The clamp assembly includes a planetary gear system for transmitting torque applied to the clamp assembly to the blade washer, wherein the planetary gear system multiplies the torque transmitted to the blade washer so that the torque transmitted to the blade washer is greater than the torque applied to the clamp assembly.