Modular Office — Wide Bookshelf File Drawer

Cut the drawer bottom from a 1x16 offcut left over from the bookcases, then trim the long edge 1" to reach the final width. Starting from a leftover keeps this an almost-free add-on.

Fasten the two 1x10 sides to the bottom with 2" screws and glue. Keep everything square — an undermount drawer will bind if the box is even slightly out of square, so check the diagonals before the glue sets.

Fasten the back to the sides, and also drive through the bottom into the back, with 2" screws and glue. Then install the drawer into the bookcase base on the 12" undermount slides — the box sets back 3/4" from the front of the bookcase to leave room for the face.

Measure the face to the actual opening — not the drawing — and fit it flush with an even gap all around, fastening from inside the box. Add a lateral hanging-file system if you'll store files. Fill any holes, sand, and finish to match the bookcase.