I have been asked to volunteer to put some glass doors on a section of built-in library shelves that can be locked to keep some of the more valuable books secure. The current shelves are built with 3/4" plywood frame with 1 1/4" x 3/4" Ash trim nailed to plywood and peg supports for shelves, and have opening of about 83" high x 33" wide. The original thoughts are making 2 doors that would be 83" high x 17" wide using 2" x 3/4" ash vertical and 3" x 3/4" top, middle, and bottom frame and then have 2 glass panes per door that would set in rabbet on back side and held in place by 1/8" or 3/16" strips screwed to back. Each door would be hinged on 4 surface mount hinge so that the door would overlap the existing trim by 1/2", and the surface hinge would allow hiding a long screw to better attach the 1" wide trim to the plywood frame. All the existing shelves are adjustable, but plan is to fix the one in middle to help lock doors.

Comments on above design, or would 2 full width doors, about 34" wide by 42+/- high be better? I think the concept of surface mount hinges and hiding strength screws will be required to make a stable mounting surface.