[R-390] White lines on knobs and more

[dog]

Common household lye -Drano- will etch aluminum too. But you'd prolly 
still want to prep it somehow before painting. It makes a nice finish on 
aluminum unless it's deeply scratched. What I've done is sand it to 360 
and then use the lye, it takes all the sanding marks off. But if you 
leave it in long enough the AL is gone, be careful out there.

On 9/11/2019 20:55, Larry H wrote:
> Thank you, John, for the nice explanation.  Your R-390 panels look very
> nice.
>
> Question - would sanding the knobs remove the oxide well enough?  Is there
> an easy way to tell if the oxide has been removed?
>
> Regards, Larry
>
> On Wed, Sep 11, 2019 at 1:53 PM John Gedde <jgedde at optonline.net> wrote:
>
>> The whole idea is to get the surface coating of aluminum oxide off.  For
>> the knobs, I bead blasted them.  For panels and what not, scotch brite
>> followed by a quick dip in diluted metal “prep and etch” available from
>> Home Depot.
>>
>>
>>
>> The coating I speak of is what Collins et al used for a surface treatment
>> on unpainted aluminim like chassis panels, the Utah plate, etc.  So,
>> getting up to speed with Bonderite gives you not only the ability to prime
>> for painting but to restore coated parts in the radio as well.  I have done
>> several unpainted panels and covers on my radios using this method.  I used
>> scotch brite brushed in one direction carefully to clean off the old
>> conversion coating the OEM put on and also to duplicate the brushed finish
>> they had originally.
>>
>>
>>
>> I’ve attached a pic of my R390 inside.  All the covers shown have been
>> restored using this method…
>>
>>
>>
>> John
>>
>>
>>
>> *From:* Larry H <larry41gm at gmail.com>
>> *Sent:* Saturday, September 7, 2019 5:47 PM
>> *To:* John Gedde <jgedde at optonline.net>
>> *Cc:* R-390 Forum <r-390 at mailman.qth.net>
>> *Subject:* Re: [R-390] White lines on knobs and more
>>
>>
>>
>> Thanks John,  Good to know about your new method.  I was wondering, how do
>> you clean and deoxidize the aluminum in prep for the dip?
>>
>>
>>
>> Regards, Larry
>>
>>
>>
>> On Sat, Sep 7, 2019 at 9:52 AM John Gedde <jgedde at optonline.net> wrote:
>>
>> Hi Larry,
>>
>> It looks great!  I have moved away from using a spray primer on aluminum
>> prior to paint in favor of a chromate conversion coating.  Loctite
>> Bonderite is what I use.  It's what we use at work for spaceborne
>> mechanisms that get painted or aluminum surfaces that remain bare
>> (non-anodized).  I've never had any issues with adhesion using this stuff.
>> Basically you clean and deoxidize the aluminum, dip it in Bonderite for a
>> minute or so, rinse and let dry.  The aluminum turns a golden color and
>> paint readily adheres to it if you spray within 24 hours.  The coating is
>> also known by other names: ChemFilm, Alodyne, Iridite, etc.
>>
>> John
>>
>>
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