My idea is to use steel angle iron across the front, ideally not too much thicker than my shelving material. For example, I'm looking at Grade A36 1"x1"x1/4".

The front edge would only be supported on the ends. The length is 64". The shelf depth is 24". The back and sides can be supported with arbitrarily large material. The shelf surface is going to be a cast acrylic sheet (the calculation for the necessary thickness of that is another problem!).

The question is how to make a reasonable calculation as to the material size needed to make the shelf strong enough. I would like the shelf to be strong enough that I could stand on the front edge without worry of it bending (I weigh 200#). In addition to my weight, the shelf might be holding 100# or so of stuff, not necessarily evenly distributed.

I've looked at the beam deflection calculator, but I'm not sure I believe the results (my best guess from the calculator was the 1x1x.25 would deflect .75" with 400#). I'm not even sure what deflection amount is reasonable... .1"? .01"?