(57) An effraction-resistant device for a lock with plate tumblers (18) comprising a casing
(1) which slidingly accommodates a bolt (9) whose tang (10) has a rack-like set of
teeth (11) for moving the bolt by means of a double-pattern actuation key and a transverse
pin (33) for locking the bolt so that it is engaged in openings (30) of the tumblers
(18) which are elongated in the direction in which the bolt slides. The openings have,
along their longitudinal edges, mutually opposite teeth (31,32) which form passages
through which the transverse pin (33) can travel by successive key turns. The tumblers
(18) have two slots (26,27) which are elongated at right angles to the tang (10) and
are engaged by respective guiding pins (13,39) in order to guide the tumblers (18),
in contrast with return springs (38), at right angles to the direction in which the
bolt (9) slides. The device is characterized in that one (13) of the guiding pins
is fixed and the other one (39) is movable and has opposite ends which are rigidly
coupled, with play, in respective seats formed in respective mutually opposite walls
of the box-like body, so as to allow movements of the pin in the slots and oscillations
of the tumblers in an inclined position; engagement means (45,47) are provided which
are adapted to engage the tumblers (18) when they are fraudulently made to oscillate
in the inclined position.
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