[R-390] Knob painting question

[Gregory W. Moore]

GE, All

Many years ago, back in the mid-70's, I happened to have the fortune to 
do some engineering for a subcontractor to Boeing.
Now, I believe all on this list are familiar with the standard Green 
Zinc Chromate primer which is used on most interior metal surfaces of 
aircraft.  Well, Boeing went a step further, and prescribed a 2-part 
Epoxy version of the same dull green (actually, it turned out semi 
gloss, but they didn't care).  Once you had baked that paint for an hour 
at 80C (176F) but a few degrees won't matter if the components can 
handle it (we were producing instruments and control surface position 
transducers, with the electronics already sealed within, so when a 
finish was specified, you had to be real sure that the cure temp wasn't 
a destruct temp--hi--.  That being said, once that was baked on for an 
hour, well, it JUST WOULDN'T COME OFF!!!.  Even EpcoStrip, which from 
personal experience can remove skin from your legs easily (neutralize 
with a drench shower and vinegar, followed by a 100+ MPH trip to the 
hospital in a police car (hey, the police officer had a grin ear to ear, 
who was I to keep him from enjoying himself), and I had some weird 
looking legs for a while --hi--... (some idjit had left a pan in a walk 
in paint booth, and I had gone down to the paint shop after hours to do 
some "government work", on (what else, the front panel of an R390A, as 
well as changing the color of a M28ASR teletype from WU livery to Navy 
livery.) the light switch was inside the booth, and I didn't see the 
pan....lesson well learned....

To put it mildly, even EpcoStrip won't budge that Boeing Green Epoxy 
Primer (I don't remember the mfg P/N, nor the Randolph P/N but unless 
environmental controls have changed all that signficantly, it still 
should be available.  I would recommend a light bottom coat of that, 
baked on, and then use Dulac Semi-Gloss lacquer (27038 per Fed-Std 595) 
OPNOTE: This is kind of simple, 17038 = gloss black 27038=semi-gloss 
black 37038 =flat black.
or Wornow Cat-L-Ink screen printing epoxy ink, which many companies will 
produce to the Fed-Std color of your
desire... if you want to start with gloss black, they also make a 
"flatting agent" which is a white silica powder which you
mix thoroughly with the thinned mix.  The only couple of things which 
are important with Epoxy paints are first, mix them
in a METAL container (I have caught too many idiots trying to mix the 
base and hardener in wax cups, ordinary paper cups,
and all sorts of other porous materials). Second, follow the 
manufacturers directions exactly (some call for mix by weight, and some 
by volume). Third, allow to react for at least 1/2 hour before using 
reducer or thinner. Fourth, insure that the reducer or thinner you are 
using is compatable with the environmental conditons in which you will 
apply the finish. Fifth, cure exactly according to the mfg's 
instructions, or to a time determined by previous experimentation.  
Lastly, don't try and stretch the
work time. These finishes all have a definite pot life. This does not 
mean that they turn into gel either, they may look just fine,
but won't apply or cure worth a counterfeit 3 dollar bill. 

    This is not to be considered definitive, I just happened to work 
designing and specifying finishing and marking materials for a variety 
of aircraft instrument dials, scales, pointers, etc, as well as the 
cases in which they were housed, as well as a lot of
equipment destined for the Navy, Marines, Air Force, and Army, as well 
as NASA and a lot of Commercial Aviation, so I developed a pretty good 
handle on this stuff.  This was additional assignments besides designing 
and building the "innards" for the prototype stuff, so I wound up with a 
fairly balanced education about finishes, as well as electronics, and 
complex analog
displays.
More info:
Randolph Products, Inc.  http://www.randolphproducts.com/index.htm

You can get copies of Federal Standard 595 (the standard color chips for 
all milspec products) by FAXING (Phonecalls don't work) to:
DODSSP (Dept. of Defense Single Stock
Point) in Philadelphia, PA. The number is (215) 697-1462. Just fax a
sheet of paper with your name and mailing address on it, and
state that you want a copy of Federal Standard 595.

Wornow Cat-L-Ink, fine mesh screens, etc:

Podgor Joseph E Co Inc 	609-663-7878 	7550 Central Hwy 	Pennsauken 	NJ 
08109


OK, I will now end this long, obtuse screed concerning paints and 
finishes, I'm sure that every member of this list has their own pet 
suppliers, and coating methods, but it really helped my mind to come up 
with these from when I was actively involved in specification writing 
and one-off prototyping.

73 es tnx de Greg WA3IVX /NNN0BVN

.

b w wrote:

> Hey Barry (III)
>
> My guess is that a roughed surface would hold the primer and paint 
> better. I used to sand-tex metal for painting, such as motorcycle 
> frames/gas tanks, cars, wrought iron, etc. Same principle. Sand-texing 
> is what you see on the nonglare parts of rifle receiver sections.
>
>
> the other other Barry, or the non-(III)
>
>> I am in the (slow) process of refurbishing a couple of sets of knobs.  I
>> have cleaned the old paint off and smoothed the surfaces with #320 
>> and #400
>> wet-or-dry paper and figured they were pretty much ready for powder 
>> coating.
>>
>> In the process of restoring some brass and other parts for my "new" 
>> Zenith
>> T.O., I was using a cotton buffing wheel with jeweler's rouge as the
>> polishing paste.  I wondered what this would do to the aluminum knobs 
>> so I
>> gave it a shot.  Wow!  The surface really polishes up nicely.  I thought
>> about giving them a coat of lacquer and letting them stay bright, but it
>> gives them a "dime-store stereo knob" kind of look so I nixed that.
>>
>> My question is will buffing them prior to powder-coating be a bad 
>> thing?  In
>> other words, will the coating be less likely to stick to the shinier
>> surface?  If it will stick, then I think the polished surfaces will 
>> result
>> in a much nicer looking knob.  Anyone tried this?
>>
>> 73,
>>
>> Barry(III) - N4BUQ
>>  
>>
>
>
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>

-- 
"All that is necessary for the triumph of evil is that good men do nothing."
                                                   --Edmund Burke

Greg Moore NNN0BVN PA
U.S. Navy-Marine Corps Military Affiliate Radio System (MARS)
Official Pennsylvania Area Website:
http://pages.prodigy.net/nnn0fbk/mars.htm
Official Northeast Area Website: 
http://www.navymars.org/northeast/index.htm
Navy-Marine Corps MARS: Proudly Serving Those Who Serve."
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