I've built a work bench by modifying some plans I found, and one part of the modification involved installing a shelf. The bench is 8' long, stable and solid, and I used 4x4x6 uprights in the back corners to mount the shelf onto.
To keep the shelf from flexing I used 2 2"x6"x8' as stringers between the 4x4s and attached the shelf ( 12"w 1/2" maple) to the bottom of one of the stringers with countersunk 2" #8 Robertson screws spaced every 12".
My question is: should I further brace this shelf considering the maximum load on it will likely be less than 100#? My suspicion is that I should install 3 triangular braces, one at each end and one in the center to prevent any sagging.
Edit: Here's the updated picture with both upper and lower. The curve in the small shelf is illusory, just need to touch it up with the router when I bullnose the front of the bench.
Best Answer
I agree, you should use some "L" shelf brackets UNDER the shelves to the vertical supports. There are many you can chose from, but even the cheap gray 10 inch ones would work fine. Remember, if you use 3 supports, the load is divided, so each bracket will only be holding apx 1/2 of the load resting between two supports. If you mount them over the shelf, rather than under the shelf, the load will be supported only by the mounting screws rather than transferring the load to the upright post, for that reason, I'd stick with mounting them under the shelf. Your shelf as pictured without braces will most likely split at the line where the mounting screws are, as the grain of the wood follows that direction.
BTW, nice workbench! Good luck