Hi Jim - for the wheel part I'd recommend using Revolve instead of sweep - anything that looks like a 360 degree turned thing is usually better done with revolve, it makes more precise geometry.

Most likely the problem is that the closed sweep has just a very tiny crease in it where at its seam point where it closes up, and filleting does not like little tangent deviations like that.

But also a different thing you can do in this case is go to into the right-side view and just rotate the wheel left by 90 degrees (select it and grab the little rotate grip and drag to the left 90 degrees).

That will move that seam area out of the zone that you are filleting so it won't really matter how smooth it is or not at that point.

It's also just a helpful thing in general to have fewer edges running into each other when doing a fillet.

So after rotation, the wheel will look like this (note seam edge is towards the front now):



Now you can do a boolean union and then select these edges:



And now those will fillet up to a radius of 0.5 or so:



You won't be able to go much larger than that because that's about all that will fit in this spot here:



But for things that look like they're incorporating some kind of circular shape in one direction, try using Revolve instead of Sweep and that will probably help make a bit higher quality geometry with a 100% smooth area where the surface closes.

- Michael