I'm still pretty new at chopping mortises and cutting the tennons that go into them, so I practice whenever I get the chance. Right now, I'm putting together a rack to store boards on. I've ripped some 2x4s into 1 1/2 x 1 1/2. I've chopped some 1/2" wide 1" deep mortises into them. Extending from the mortises will be 1 1/2" x 1 1/2" x 12" (13" if you count the length of the tennon). I'm planning on putting a small diagonal between the vertical and horizontal, maybe 3" out the length of the horizontal. These will be attached to the wall studs. I have 3 levels, approximately 12" apart. I'm guessing I can store up to around 12 2x6s on each level. I don't have any question on the strength of what I'm building, but it got me to thinking.
Is there a way to determine how much weight a tennon, supported only on one end, can hold by itself before additional bracing is needed. In other words, in my construction, how long could I make the horizontal without the diagonal below or for a particular length how much weight can it support?
I hope I worded that clearly.