Robert Bonner wrote:
> I thought we covered this last week. You don't want to use LYE on aluminum
> unless you want it to GO AWAY. It dissolves it, acid works more controlled.
> Lye would cause more pits.
>
I gotta jump in here.
Lye, if used with a bit of intelligence, does not "dissolve" aluminum.
At least not any more then you would want to in the first place. I use
the stuff all the time on aluminum and it works great for putting a nice
matte finish on parts and is a reasonable surface prep prior to painting
if you don't have the resources to do a professional prep.
As far as the air variable cap surfaces, all the Johnson and Caldwell
caps I have seen appear to have had the plates tumbled. Depending on the
tumbling media used, the surface can be nicely de-burred down to the
microscopic level and leave anything from a matte to a polished finish.
Although I have the resources to tumble small parts, I don't have to
patience to do it. A proper job may take several days depending on the
media used and the type of "polish" desired.
If I were to re-build a air variable with the resources I have here, I
would dis-assemble it and using 400 grit wet-or-dry paper carefully take
off the high spots. Then I would do a light etch with lye (sodium
hydroxide). The lye will etch away all the microscopic ridges left by
the sandpaper and leave you with a nice matte finish that will look good
under the microscope. Any "potholes" that might be left on the plates
won't matter as long as there are no high spots or sharp shapes or edges.
As has been said here recently, never dump parts in lye that have blind
holes tapped into them. I have not had any problem with drilled and/or
tapped holes in sheets or plates, but have had a bit of trouble with
blind holes. Of course, I use a lye concentration suitable for the job
at hand and watch it all the time it's in the bucket.
The acid wash has always been a problem for me as the acid I would like
to use is much more difficult to obtain then sodium hydroxide. Has
anyone used white vinegar for this?
73, Larry
--
Larry - W7IUV
DN07dg
http://w7iuv.com
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