Security lock for sash window

A security lock for use in a double-hung sash window assembly having upper and lower sash window frames installed for vertical reciprocal sliding movement, one relative to the other, said upper sash frame having a recess into the interior thereof, said security lock comprising:

• a casing adapted to be disposed in said recess having an opening to a substantially rectangular cavity disposed therein, said cavity including an upper, a lower and a back wall;
• an elongated tumbler disposed in said cavity, said tumbler including a substantially arcuate upper portion with an apex protruding from said upper portion, forward and rear edges with an ovate slot disposed midway between said edges, a pocket disposed in said rear edge adjacent to said arcuate portion, an inclined lower edge, and a wedge-shaped indentation disposed below said apex in said arcuate portion;
• a sidewall overlaying said cavity, said sidewall including a pivot lug secured thereto, said pivot lug adapted to be inserted in said tumbler ovate slot for movement of the tumbler relative to the sidewall between a retracted position and a locking position;
• a leaf spring mounted between said lower wall of said cavity and said pocket, said leaf spring normally biasing said tumbler to protrude beyond said opening into said locking position;
• and,
• a wedge-shaped protrusion extending from the upper portion of said cavity back wall, said protrusion engaging said tumbler wedge-shaped indentation in an interlocking manner during movement into said locking position, such that said tumbler wedge-shaped indentation creates a vertical component force directed downwardly into said protrusion, so that said tumbler resists further rotation, resists deformation of said cavity back wall, and prevents relative sliding movement between said sash frames.