First - this isn't a big deal if the rent isn't riding on the progeny..
Trying to refine genetics to keep the best and sift out the problems? Inbreeding will do it as long as you are willing to cull.
Commercial operation trying to maximize outputs? Inbreeding is the opposite of what you need and will cost you money.
This isn't as scary as most folks say as long as you know there can be problems - 3 headed monsters are not the problems you can expect. Like Travlr said, fertility will take a hit as well as longevity and all of the lowly heritable traits. In my experience, you will probably have a fine calf and not think about it again. Not to be too vulgar but the only reason people freak out about inbreeding is because they compare it to humans which are much more difficult to cull.
If you know what breeding your bull comes from, I would compare his pedigree to the Angus genetic defect list. There is a long list that is worth the time to run through. A lot of bulls have been cleared through DNA testing but not many females. If you don't see any potential carriers in the last 3 generations, I wouldn't worry about it.
"The limit" will be dictated by the gene pool you have along with luck. At some point the calves will be less fertile but that could be 4 generations later - there is no way to know. If it works for you and you are OK with the relatively low risk of real problems, have at it. All animals have genetic issues and you are more likely to find them this way but the good part is that with every generation, you have improved your stock if you don't see any problems.