[R-390] Painting Knobs

[Barry]

As I've mentioned over the past several months, I'm in the process of refinishing the knobs (as well as all the other front-panel parts) for my R390.  I stripped, sanded them and used Rust-Oleum Self-Etching primer and painted them with Rust-Oleum enamel.

The Rust-Oleum Self-Etching primer and Rust-Oleum enamel worked very well on the front panel, escutcheon, meter covers and, as far as I know, the large knobs.  I had reason to remove the paint (again) on the larger knobs and the paint and primer stuck quite well; however, I've discovered that the primer doesn't seem to stick very well to the smaller knobs.

While working on the smaller knobs, I noticed a small chip in the paint on one of them that exposed the bare metal.  I don't know exactly how that chip was made but I think I dropped one of the knobs onto the table top which might have hit it just right.  I noticed I could take a sharp putty knife and some of the surrounding paint could be removed all too easily.  Another knob had a very small spot where the bare metal was exposed as well.

I decided to dump those two (and a third one that had some small defects in the top coat) into a can with acetone and, after a short soak, I pulled them out.  The paint had wrinkled quite well and was very easy to remove (it virtually fell off); however, the primer also came off very easily which was different than some of the other pieces I'd painted.  In fact, the primer and paint stuck very well to each other but the entire paint/primer fell away from the metal.

I think those knobs are die-cast aluminum so I can't explain how/why the primer wouldn't have stuck to those the same way as the other aluminum parts but I just don't know.

Anyone have a similar experience and, perhaps, have a suggestion for a better primer?  I think the factory used conversion (Alodine?) process on most all of the aluminum parts and that would probably be a "best" solution.  I had some parts done that way many years ago around here but it was pretty expensive and I'm not sure it's even still an option around here.

Thanks,
Barry - N4BUQ