I needed a shelf with very little depth to sit on my drafting/painting/sculpting/everything table. All shelves for purchase were fairly deep, which would take up too much of my work area.
I modeled the brackets around some cheap spruce boards I picked up at Lowes for $1.49 per 8 feet. https://www.lowes.com/pd/Spruce-Pine-Fir-Furring-Strip-Common-1-in-x-4-in-x-8-ft-Actual-0-718-in-x-3-437-in-x-8-ft/1000016907
The only dimension that matters when you buy the boards is the thickness, Lowes lists this lumber as 1" with an actual thickness of 0.718".
I press fit this shelf together, pre-drilled the four holes in the T-Joints, then used small screws to attach the T-Joints for good. The corner pieces are a friction fit. No Glue Necessary!
Flip the pieces on their backs in Cura/Simplify3D.
The angle braces are designed to print without supports.
No glue works for me, but I'm not loading it down too heavily and the shelf isn't too big... but time will tell.
Designed with Fusion 360 and a cheapo digital caliper.