A method enabling key operation of a clutch thumb-turn cylinder whether or not any force is applied to the thumb-turn, comprising angled lug or lugs on the cam drive proximal in relation to the thumb-turn (proximal cam drive) and angled lug slot or slots on the cam inner flange. The proximal cam drive lug or lugs are angled such that when viewed from a superior aspect the lug profile is substantially an isosceles trapezium. The sides of the cam flange lug slot or slots are angled so as not to exceed the angle between the non-parallel sides on the proximal cam drive lug. The angled sides of the proximal cam drive lug and cam flange lug slot significantly reduce the radial forces exerted in a barricade-type situation, thereby reducing the horizontal force required for the key to disengage the proximal cam drive, engage the distal cam drives and successfully operate the cam to unlock the door. The invention is intended for use in such environments as hospitals and public buildings, etc and in use will enable the room occupant a degree of privacy under normal circumstances but will allow the key holder to gain access to the room when necessary, for instance for medical or safety reasons.
展开▼
