Replacing the chuck on your electric drill is not as difficult as it may seem. The drill key that comes with your chuck is for removing the chuck as well as tightening drill bits. However, the chuck key can be difficult to work with when removing the chuck. The best way to remove the chuck from an electric drill is to use an Allen wrench. This process will work for keyless chucks as well.
Twist the chuck with the chuck key to the fully open position.
Look inside the centre of the chuck to locate the head of the Phillips-head screw that secures the chuck to the drive spindle. The screw is a left-hand thread screw. Remove the screw with a Phillips-head screwdriver, turning the screw clockwise to loosen the screw from the drive spindle.
Insert the short end of a ¼-inch Allen wrench into the drill chuck where the screw mounts. Tighten the chuck around the Allen wrench with the chuck key, just like you would a drill bit.
Lay the drill on its side on a flat surface. Hit the long end of the Allen wrench with a hammer to loosen the chuck from the spindle. Hit the Allen wrench so that the chuck turns in a counter-clockwise direction.