I need to install some heavy granite contertop (650mm depth) on masonry walls, and I have a lot of angle iron (1 1/2" by 1/8") and U channel (70mmx30mm x 5/64") leftover and thought about welding them myself.
I do remember something about levers and pull strenght, but I don't quite remember how to calculate the ratios of horizontal and vertical legs to get a good support. Can anyone enlightmen me?
I thought about using at least 300mm (1 ft) on the vertical leg, but using angle iron I will be able to use only 2 bolts (one at the top and 1 at the bottom, since the middle doesn't really need to be bolt because most of the force is at the top).
Another choice that I have is using 4mm (5/32") plate as the backing (which goes agains the wall) about 100x100 in size welded to a U channel (5/64") cut in a sort of triagular shape (like the image below). This will allow me to have 4 bolts (2 on top and 2 on bottom) on the backplate.
The first design has less bolts but a longer leg, the second has more bolts and large footprint, but a shorter vertical span. What would be stiffer/stronger?