[R-390] Painting Knobs

[Jim Whartenby]

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 <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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