There is no way you are bending 3/16" steel on a 1/4" radius in a small homebuilt brake. How clean of a bend do you need? What I would do is get a piece of 1/2" diameter bar, mill it to a half round, them mill out the inside radius. Weld that to the end of your flat stock. Voila
Another method would be to heat and beat it around a piece of bar stock, but this would not be neat and clean.