How to make and install a corner shelf joint

For a corner shelf, the joint is the most important where the boards meet.  Although shelf brackets can be used to hold the shelves where the joints fit, the less brackets used at the corners give a professional effect to the project.  An alternative method is to use plywood.  The exact shelf size (90 degrees shelf) is marked out and cut from it, but there is a lot of waste plywood material for a small project.

Economically, using a dovetail type joint (with regular shelf boards) for the corner shelf is the better way to achieve the best results.  The joint gives the impression of a butt joint, but at a closer look from above eye level shows a mortise and tenon joint except the tenon slants down at a 45 degrees. The slant prevents the tenon cut from slipping off the other trenched piece when joined.  Also a view from the bottom shelf shows a simple mortise and tenon except the joints slope upward.

Whether it is a left or right hand corner shelf, one board is cut as a tenon dovetail and the other board is cut to receive the tenon dovetail.  For a left-hand corner installation, the right shelf is cut to the tenon and the left shelf is trenched to receive the tenon.  The opposite application is applied to a right hand corner installation.  Whereas for a "U" shaped shelf installation, the centre or middle shelf is cut to a tenon type joint and the outer shelf is marked to receive the tenon dovetail.

The shelf tenon size is marked to about one fourth the width of the shelf with the tenon protrussion marked at 3/4" thickness of the board.
The tenon is marked with the dovetail (45 degrees angle) angle pointing downwards.  Butt the two boards together at 90 degrees and transfer the marks to the other corner board.

Use a dovetail saw or backsaw and a bench vice to cut the tenon and the trenched dovetail of the two boards accordingly and then test fit the pieces together.  Adjust the cuts for a snug fit.

Shelf brackets are installed along wall to support the shelf at intervals spaced at 32' spacings, but not exceed 48' spacings if large objects are placed on shelf.

From the corner, a shelf bracket may be placed at 16 inches to support the trenched shelf, but for the tenon shelf, brackets may be spaced at 32 inches away from the corner.

As the corner shelves are joined together, ensure a proper fit.  A strip of steel bracket is fastened to the front underside of the shelf

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