[R-390] Painting Knobs

[robert meadows]

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


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 <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
>> ______________________________________________________________
>> 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
> ______________________________________________________________
> 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
>  
> ______________________________________________________________
> 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
______________________________________________________________
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