[R-390] Painting Knobs, Drawing Spec

[Barry]

Interesting. Perhaps that explains why the primer adhered so well to the large knobs. 

Barry - N4BUQ 

> I'm looking a the drawing for a small knob. it says:
> MATERIAL: ZINC BASE ALLOY, DIE CAST, ASTM-B-86-577 ALLOY AG40AB
> MAY BE SUPPLIED BY DOEHLER-JARVIS CORP, CHICAGO.

> Drawing for the large knob says:
> MATERIAL: ALUMINUM BASE ALLY, DIE CAST USING ALUMINUM ALLOY NO 13 IN ACCORDANCE
> WITH FEDERAL SPEC QQ-R-591

> same vendor as small knob.

> Tom

> On Monday, August 12, 2024 at 10:38:39 AM CDT, Barry <n4buq at knology.net> wrote:

> Tom,

> I really wish I had glass bead or other media blasting available. That would
> have saved me so much time!

> After getting as much of the existing paint as I could with Aircraft Paint
> Remover, I resorted to hand-sanding with 320-grit silicon carbide paper. That
> left a shiny but not too slick of a finish. I really don't know why the primer
> didn't stick to it.

> I went with full gloss and not sure if that was the best choice (I don't
> remember what sheen I used long ago) but it looks okay. If this paint job does
> fail with use, then at least it's easy enough to remove...

> Thanks again,
> Barry - N4BUQ

> > Barry,

> > I have done several sets and just finished up one the other week. I used to wire
> > wheel the old paint of but have since transitioned to using my glass bead
> > cabinet. This provides a little "texture" for the paint to grip to but not
> > enough to show through to the finished coat.

> > I have also used the self etching primer with good results. For the last two
> > sets I used Rustoleum semi gloss / primer in one. This worked well also.

> > Tom
> > W3TA

>> On Monday, August 12, 2024 at 10:13:31 AM EDT, Barry < [
> > mailto:n4buq at knology.net | n4buq at knology.net ] > wrote:

> > 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
> > ______________________________________________________________
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