[R-390] Painting Knobs

[Barry]

If I could justify a gallon of it and a spray-gun. That's why I stick to rattle-cans and the troubles they bring. 

Thanks, 
Barry - N4BUQ 

> Use better paint. Sherwin Williams Acrolylon 218 is my recommendation.
> R

> [ https://more.att.com/currently/imap | Sent from AT&T Yahoo Mail for iPhone ]

> On Friday, August 16, 2024, 12:49 PM, Barry <n4buq at knology.net> wrote:
>> From what I've experienced with these knobs as well as knobs I worked on many
>> years ago from some R-390A models, I suspect they were painted with polane or
>> something equivalent. Aircraft stripper used to work on that fairly well but
>> not so much with the newer stripper. No other chemical I tried would cut it and
>> the primer is even more difficult to remove.

>> The more I read about DIY power coating, the more I'd like to try it. I had some
>> knobs powder coated many years ago but the place where I had that done applied
>> a much-too-thick coating and I wasn't very pleased with it. I think the DIY
>> powder may be different from what they used and perhaps I could control the
>> thickness better. If that would work, it would probably be the best method.

>> Thanks,
>> Barry - N4BUQ

>> > I found on line Mil-F-14072, the spec on finish, that is listed in the knob
>> > drawings. Both knob finishes (P516D and P612D) have been deleted from the 4
>> > October 1990 dated document. So no help chasing documents to find the paint
>> > and process descriptions.
>> > Curious that the Final Engineering Report on the R-389/R-390, dated 15 Sept 1953
>> > says that the Manufacturing Drawings and Specifications may be used to
>> > supplement this engineering report. But the drawings for the knobs are dated
>> > January, 1956 both of which list the original R-390 (non A) contract
>> > 14214-PH-51-93.
>> > It seems to me that about two years and four months is a long time to go through
>> > the drawing approval process! Perhaps there was an earlier set of drawings
>> > just for the non-A design?JimLogic: Method used to arrive at the wrong
>> > conclusion, with confidence. Murphy

>>> On Friday, August 16, 2024 at 10:33:47 AM CDT, Barry < [
>> > mailto:n4buq at knology.net | n4buq at knology.net ] > wrote:

>> > Also, I cleaned the surfaces with acetone and let that dry (very quick drying
>> > time for acetone) before priming.

>> > Barry - N4BUQ

>> >> Jacques,

>> >> I allowed the primer to dry overnight, painted the top coat, set it in the sun
>> >> for a couple of hours to help the curing process, let it sit overnight, and
>> >> then tried the scratch test. I'm not so much concerned about the top coat
>> >> being all that hard at that point but I am concerned that the primer doesn't
>> >> want to stick to the metal. I wouldn't think the primer needs heat curing to
>> >> stick, would it?

>> >> Thanks,
>> >> Barry - N4BUQ

>> >>> Barry, IMHO, if you tried a "fingernail test" just few hours after the knob
>> >>> was painted, it is normal.
>> >>> Most paints can take a week or more to harden.
>> >>> The trick I used was to put mine under the summer sun once they were painted
>> >>> with the Krylon Dual-superbond, and they were "holding" such fingernail
>> >>> test.
>> >>> You can also use a small oven at 200F to promote the paint hardening.

>> >>> 73, Jacques, VE2JFE in Montreal

>> >>> Welp, I give up. I tried priming one knob with a non-etching primer and a
>> >>> top coat. I can take my fingernail and easily scratch the paint off down to
>> >>> the bare metal. Sigh... Maybe I'll have them chrome plated.

>> >>> Thanks,
>> >>> Barry - N4BUQ
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