Hole cutter having detachable hole-sawing blade

A hole cutter comprising:

• a shaft having a bottom open chamber in a bottom side thereof, an inside hole axially upwardly extending from said bottom open chamber toward a top side thereof, and a locating hole extending transversely and communicating with said bottom open chamber, said bottom open chamber having a polygonal cross section;
• a ball movably mounted in said locating hole of said shaft;
• a socket capped on said shaft and movable axially relative to said shaft, said socket having a tapered inside wall contacted with said ball and movable with said socket relative to said shaft between a first position where said ball doesn't project into said bottom open chamber and a second position where said ball is forced by said tapered inside wall to project partially into said bottom open chamber;
• a spring member sleeved onto said shaft for supporting said socket in said second position;
• a hole-sawing blade assembly having a connector detachably fitted into said bottom open chamber of said shaft, and a cylindrical hole-sawing blade connected to said connector, said connector having a polygonal cross section that fits the polygonal cross section of said bottom open chamber of said shaft, an axial center through hole, and at least one locating recess at an outside wall thereof for receiving said ball to lock said connector to said shaft;
• and
• a drill bit having a shank inserted through the axial center through hole of said connector and fitted into the inside hole of said shaft.