i think the OP is looking for a more specific answer..
OP if you use the search function, there are a TON of threads on the subject of in or line breeding with snakes.
http://ball-pythons.net/forums/showt...ght=inbreeding
http://ball-pythons.net/forums/showt...ght=inbreeding
http://ball-pythons.net/forums/showt...ght=inbreeding
http://ball-pythons.net/forums/showt...ght=inbreeding
http://ball-pythons.net/forums/showt...=line+breeding
I've read before that some corn snakes are on their 11th generation of line breeding in some cases and they are just beginning to see issues associated with that. Ball pythons aren't past 6 generations. But i cant remember the source, i'm sorry.
With inbreeding, there is always the possibility of passing along an unwanted gene with a wanted one. I've heard of breeders actually trading or selling off certain females or males in their collections and getting some new animals to get new blood into their collection every some-odd years.
Just because you line breed for a few generations dosen't automatically mean that your animals will hatch with no eyes, kinks or deformed heads. There are also other things that cause these problems like incubation problems, etc.
There isn't a "set" number of times to breed mother to son or father to daughter or brother to sister. Its really just something that you as a breeder would need to deal with.