Insert the blade of a flat screwdriver into the chuck where you would normally insert a drill bit or screwdriver attachment into your Craftsman drill.
Turn the screwdriver clockwise by hand, loosing the retaining screw inside. Be sure not to turn the screwdriver counterclockwise, the normal direction for backing-out a screw, or you may strip it.
Put your Craftsman cordless drill on its lowest gear setting. Wrap it in a cloth and put it in a table vice. Tighten the vice to hold the cordless drill but not too much to avoid cracking the casing.
Find the largest diameter hex wrench that will fit inside the cordless drill's chuck and slide the short end of the wrench inside the chuck.
Attempt to tighten the chuck by hand, if it will not turn, strike the long end of the hex wrench with a hammer in a counterclockwise direction to break the chuck free. You can now take your Craftsman drill out of the vice and pull off the chuck; it should now rotate freely to allow the insertion of different bits.