The most common hidden shelf brackets are part of a floating shelf design, where the bracket is hidden in the hollow core of the shelf itself. However, if you don't have a floating shelf available, you can invert the concept to build a clean lined bracket for any shelf. Though it requires some precision cutting, this project is still appropriate for novice to intermediate do-it-yourselfers. Set aside a full afternoon for this project, which will leave you plenty of space to take your time and get it right.
Measure the thickness and length of your shelf.
Cut three wood strips to a length equal to the length of your shelf, plus 5 cm (2 inches). For example, a 75 cm (30 inch) shelf would need strips cut to 80 cm (32 inches) long. Take the width of your saw blade into account while cutting.
Cut two other wood strips to a length equal to the thickness of your shelf. A 2.5 cm (1 inch) shelf would need one-inch strips. Take the width of your saw blade into account while cutting.
Arrange the two short strips and two of the three long strips into a rectangular frame. The 5 cm (2 inch) edges of the short strips should about the 5 cm (2 inch) faces of the long strips. Glue in place, then reinforce with three 4 cm (1 1/2 inch) wood screws per connection, a total of 12 screws.
Cut the remaining strip to a width that matches the total width of the frame you've built. Mount that strip to the back of the frame using wood glue and six evenly spaced 4 cm (1 1/2 inch) wood screws per long strip.
Sand all faces of the bracket. If desired, paint or stain to match or complement the shelf.
Mount the bracket to the wall using 7.5 cm (3 inch) wood screws, each drilled through the back plate and into a wall stud behind. Position the bracket so it crosses at least two wall studs.
Coat the inside of your bracket with wood glue. Slide your shelf into the bracket, then screw in place with one 4 cm (1 1/2 inch) wood screw for every 5 cm (2 inches) of board length. Screw in place on both the top and bottom faces. Wipe away excess glue.
This will work for knick-knack shelves or other shelves that support a light load. Hidden bracket shelves aren't suitable for heavy loads such as book shelves or entertainment centres.