A clamping assembly is provided for retaining an accessory on the spindle of a power tool. The clamp assembly preferably includes a planetary gear system for transmitting torque applied to the clamp assembly to the accessory, wherein the planetary gear system multiplies the torque transmitted to the accessory so that the torque transmitted to the accessory is greater than the torque applied to the clamp assembly. An extendable lever or a handle may also be included for increasing the amount of torque applied to the clamp assembly by the user. A clutching system may also be employed to prevent the user from over tightening the clamp assembly