Usually, I'll hinge the surfaces after the final primer coat and then spray the base, trim, and clear coats on the assembled model.

The trick I learned is to spray across the hinge line, never directly down into the hinge line. As you pass the gun along the span of the wing (or stab), just cock your wrist slightly so the gun is angled away from you. When you hit the hinge line, you will spray at a slight angle and not get too much paint build up in the gap. I use Klass Kote epoxy and a few light passes are all it takes to get good coverage.

It just takes practice. Hope this helps.

Ron

When using pin hinges, I normally paint all my control surfaces first then install the hinges.  Presently, I'm working on a model that I want to maiden in primer, then final paint after some test flights.  The plane is electric so there's no problem with getting oil on the finish.  Do I need to take any precautions to prevent the paint from affecting the hinges?

I think I remember hearing Bob Storick saying that he prepares the hinge slots and then uses a set of "painting hinges" he keeps around to temporarily mount the flaps to the wing and the elevator to the stab.  After the finish is cured and mostly rubbed out, he permanently installs the flaps and elevator with new hinges.  He puts the "painting hinges" in a box for the next project.

Did I get that right, Bob?  It is a clever idea and a good use for some of those hinge sets that are furnished with a kit but unuseable.
regards,
bill marvel

JFV:
I used to build like that all the time, then painting with technique like Ron suggests helps.

On a practical note, if you are using a dope finish it really does not stick to nylon hinges very well!  After painting you can go in with an Xacto and pick any offending paint off pretty easily...