Preparing Aluminum Parts
These tips for measuring, cleaning, and
preparing the aluminum parts of your kitplane will really pay off in
saved time, effort, and frustration.
GREAT! But the size
they say to cut the pieces often
the first part I made
didn’t have edge distance, I learned to leave the pieces a little
the plans call for until all the holes are drilled, THEN cut it down to
found a couple of
times that after I had drilled the holes through
the skin and into the supporting structure that the holes in the
supporting structure didn’t have the required edge distance.
biggest spot this happened was after I set the center spar sections of
the fuselage to match the distance between the wing spars.
on the seat and baggage ribs weren’t long enough to give me edge
distance on the outside two rivets.
this happens to you,
it isn’t the end of the world. Of course, if it is easy to
aluminum parts and swap them out, you can do that. But if you
easily replace a part, you can add a doubler. Use a scrap
aluminum that is
at least as thick as the piece without edge distance. Make
extend to the rivet holes on either side of the questionable
Then when you rivet it all together, include the doubler on those three
holes and you are good.
This is a very important
step. Don’t get in
such a hurry
that you skip
it. By dressing all
the edges of your aluminum parts, you
remove any stress points and ensure proper fit.
Stress will build any place that there is an
cutting process used
by Vans leaves
little burrs or sharp edges on most pieces, and leaves little
thicker parts. All
imperfections need to be removed.
rule of thumb is to run your fingernail along the edge of a part. If you can feel the bumps,
you need to do
more edge dressing. Don’t
the inside of lightening holes, they need de-burring too.
I used a burnishing tool,
de-burring tool, at
first. But I wasn’t
real happy with the
results, so now I start with a file if there are heavy burrs, and
emery cloth. As an
parts are easy to edge dress using a Scotchbrite polishing wheel
mounted in a
Prime everything! I
have spent enough time doing corrosion control work on airplanes, thank
you. A lot of
builders don’t prime their
aluminum parts, they just alodine them.
really want to take the chance that your plane will rot away? If you live in New Mexico or Arizona,
and don’t ever plan on going cross-country or selling your plane, you
probably get away without priming.
is one of the things I look for and tell others to when looking into
a plane. If it
isn’t primed on the
inside, be very cautious.
I used 3M Alumiprep as
the first step. This
is the acid etch
process. It will
remove any grease, oil and dirt from
the part. Don’t go
touching the parts
after you clean them. Make
sure you are
wearing gloves to both protect your hands and to keep your hand oil off
parts. All you do
is mix a little Alumiprep
with water, then wash the parts like you do dishes at home. Get the bubbles going and
well. The writing
on a lot of the parts
will come off on this step. This
help you know you’ve done a good job.
Rinse the parts with water, and let them dry. They should now be dull
instead of shiny.
Next I alodined the parts. This is the step that
turns the aluminum parts
gold. Actually, the
comes from a dye
that is added -- it has nothing to do with the chemical reaction. It is added only so you
can see the
progress. As the
alodine gets older, the
dye doesn’t work as well. Follow
directions for how long to leave it on the parts, don’t rely only on
color. You can
completely immerse parts
in the alodine, or use a spray bottle to spray the larger parts. After the required time,
rinse with water and
let dry. Depending
on the exact aluminum
makeup of the parts, some will end up more gold than others.
Last is the primer. I
used Dupont’s Veri-prime (primer #615 and converter #616S) because it
easiest to get locally for me. Probably
any brand-name two-part epoxy primer is just as good.
I say that already? Don’t
forget the dimples on the outside of
the skins. Those
need priming too. Most
of the corrosion work I have had to do
is around rivets. The
and the fact that the rivet hole cuts through the alclad probably
the faster corrosion in this area.
can see the primer stripes on my parts in my pictures.
I’m not worried about the skin around the
dimples; I will treat that when I get to painting the outside of the
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