Im using a procedural crater shader but the rims on them are very sharp, is there anyway to smooth them out so its not a solid edge
Lower rim tightness and raise rim softness will do the trick. Or you can shape one by subtracting 2 Simple Shapes.
i must be doing it wrong
(http://img401.imageshack.us/img401/3492/20257529.png)
Maybe unclamp your whites and blacks...