Self-contained security lock for double-hung window

Claim 1

A self-contained security lock for use in a double-hung sash window assembly having upper and lower sash window frames formed of assembled header and hollow stile members and installed for vertical reciprocal sliding movement one relative to the other, a stile of said upper sash frame having a recess into the interior thereof from a side of the stile, said security lock comprising: A. a casing having an internal cavity, a faceplate overlaying said cavity having an opening into said cavity and a pivot lug in said cavity secured to a wall of said casing, said casing adapted to be installed in said recess with said faceplate surrounding the perimetric edges of said recess; B. a leaf spring having opposite ends and mounted in said cavity; C. an elongated tumbler having upper and lower ends with said upper end pivotally mounted on said lug in said casing and said lower end being movable between a locking position and a retracted position in said opening of said faceplate relative to said header of said lower sash frame; D. said leaf spring having one end engageable with said lower end of said tumbler normally to bias said lower end of said tumbler to protrude beyond said opening into said locking position to engage against said lower sash frame and prevent such relative sliding movement between said sash frames; E. said pivitally mounted tumbler being retractable manually into said cavity to disengage said lower end of said tumbler from said lower sash frame header and permit such relative sliding movement between said sash frames; F. said second end of said leaf spring being restrained within said cavity; and G. said tumbler including a countoured recessed surface extending along the length of said tumbler, said recessed surface including a stop member, said one end of said leaf spring being slidable along said recessed surface during pivotal movement of said tumbler between said locking position against said stop member and said retracting positions away from said stop member.