Shelf supports with double tenon joints

I needed to build another shelf for the basement. Rather than use the same design as my other shelves, I decided to make some shelf supports using double tenons joints. I figured this application was also a good one to put the strength of double tenon joints to the test.

Usually I round off my tenons to fit in the mortises from my slot mortiser, but for a change, I decided to square out the mortises. These are 3/16" tenons, so 3/16" chisel is perfect for squaring out the ends. The force required was just a bit more than I could easily push by hand, so I ended up using a mallet.

I cut the double tenon using my Delta tenon jig. I cut out the space beteen the tenons by making a series of cuts to remove all the material. I ended up doing the same for the shoulders of the tenon because these were narrow enough that I could clear them out with two passes with a saw blade.

Checking the fit of the double tenon. Double tenon joints are a bit more finicky than regular tenon joints because both tenons and the distance between them needs to align precisely.

(Update 2009): I have since built my multi slot mortising machine for quickly and accurately cutting multiple mortises, and use my screw advance box joint jig to accurately cut multiple tenons. As such, I don't have to fuss much to get double tenon joints to fit perfectly anymore.

And here's one of the shelf support brackets mounted on the wall. I just screwed them into the sides of the studs on the unfinished side of a wall.

For the shelves themselves, I used some old bi-fold closet doors. These are just strong enough for the job. Not ideal, but I had some lying around, so there was no need to buy anything.