[Bitter Dawn]

Lots of practice! Use your diaphragm for your screams, it should be a technique that's sort of inbetween actually yelling/screaming and creating a harsh tone of your vocals, I can't imagine you can produce a loud and harsh noise properly without really using your lungs.

Describing vocal technique is a hard thing to do, I've read alot of post on forums and so called guides online and all I can ever get out of it is that screams shouldn't hurt, and practice is pretty damn important.