One of my biggest issues is fillets I must not have enough training on the rules and how to know they work cause I can not seem to get them to work every often. and since you have to add them at the end of the design this takes a great deal of time and more than not they just do not work. Can anyone tell me how I can insure not to have problems? I work in all surfacing. Like it will work one way but not another, I have done some research and I can not seem to find any rules to insure it will work. I need a 15mm radius around the whole top edge I know this can be done cause I can machine it that way so if I can machine I should be able to design it. But this is an on going problem for me so if anyone can tell me a way to insure this will always work I would appreciate it lots.
"Insure" is a strong word. You need a magic wand for that.
The big problem with this part is that you have a lot of surfaces that are almost tangent/parallel/flat. When you try to fillet edges on opposite sides of an almost tangent edge, things get really weird, fillets want to extend out to infinity, or there abouts. The first thing you have to do to "insure" fillets work on this part is to clean up the junk. To do this, you're probably going to have to go back to the original model. You could deconstruct your part in surfaces, but it would take a lot of time. The pair of edges that go along most of the part and are almost parallel to the edge here at the top of this image are a huge buzzkill.
One thing you can try is to RMB and Select Tangency to actually select each edge you want to fillet. Don't rely on Propagate to Tangent, because you don't know which edges aren't actually tangent, and when it decides an edge isn't tangent, it will just stop. Also, use the preview thing. It slows you down a lot, but it will give you an idea if the fillet will work. You can also try doing the fillet in sections, making as much of it work as you can, and then hopefully you'll eventually get all of the edges. It's a long way from "insure" to be sure.
There's a whole list of things you can try, like face fillets, variable radius fillets, trimming out an area and using Fill surface to manually create fillets. The biggest thing is to clear out the junk. You might be able to use Delete Face to clear some of it. And then sometimes when you're really desperate, the method you already mentioned is the last resort. CAD can't do it, but CAM can, so just machine it.
For future reference, it's really tough to make some of the tangencies in your part using surfaces and some of them using fillets. If you do that, you have to make sure your surfaces are perfect. This part has areas that are just a mess, from a filleting point of view. Always strive for as few broken up faces as possible, and where faces have to break, make sure they are at least c1, hopefully c2 (tangent vs continuous curvature). The fact that some of your phantom edges turn solid should be a clue that you've got some problems.
Best of luck.