My impression is that bowl feeders, once you get beyond the very simplest designs, take a considerable amount of tuning, requiring some real specialized skills and experience. The basic vibratory bowl or centerboard bowl is not the hard part, unfortunately. The sorting, indexing, and conveying parts are the "skilled art" parts.
If you just want flat parts with roughly 1:1 aspect ratio (e.g., nuts or washers) to advance up a ramp and out of the bowl in single file, that's not too hard. If you need to line up parts with a larger aspect ratio (e.g., needle bearings), that requires more work. If you want asymmetric parts to be oriented consistently, that requires even more work, although headed parts (e.g., bolts or machine screws) are rather easier to deal with than some other shapes. If you want basically cubical parts to be oriented consistently, that requires a whole lot more work.
The sorting and indexing mechanisms are often ingeniously simple. But they take a lot of time and experiementation to perfect. If you're a specialist who's done this for decades, you already know what works in a lot of cases. If you are a generic machinist and hands-on mechanic, figuring it out from scratch could take weeks or months of messing about.
When I was at the University of Wisconsin in Madison in the late 80's, I ran across a collection of detailed studies of bowl feeders in the engineering library. It was the first time I'd seen that stuff anywhere outside of "how it's made" style industrial movies (which today would be Youtube clips). The only reasonably common place I've seen this sort of thing published is in the four-volume set Ingenious Mechanisms for Designers and Inventors edited by Franklin Jones and published by Industrial Press. Volume 1 has about 50 pages of example feeding mechanisms, but there's nothing like a general introduction or guidelines; it's all just examples. The other three volumes are similar. There are probably specialized texts on this subject, but I don't have any to refer to.