[R-390] Painting Knobs

[Jacques Fortin]

Barry, the knobs of the R-390s are not made of aluminum, it is a zinc alloy
that is used in a die-cast process.
I obtained the best re-finishing results (after many disappointing trials)
by using a Krylon "Dual Superbond" paint-primer product, providing that the
knobs were thoroughly cleaned in lacquer thinner first and not touched by
bare hands before painting.
I do not know if this product is available on your side, but I suppose that
it is.
Good luck with your restorations.

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la
part de Barry
Envoyé : 12 août 2024 10:07
À : R-390 Mailing List <r-390 at mailman.qth.net>
Objet : [R-390] Painting Knobs

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
______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
-------------- next part --------------
A non-text attachment was scrubbed...
Name: IMG_4344.JPG
Type: image/jpeg
Size: 2427989 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/r-390/attachments/20240812/464db361/attachment.jpe>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: R-390A Small Knob.pdf
Type: application/pdf
Size: 1190057 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/r-390/attachments/20240812/464db361/attachment.pdf>