Scotch Brite - what grade do I use?

[KDOG]

What grade Scotch Brite do I use on the main tubes to buff out the little surface imperfections? Or does anyone know the proper way to sand them? Thanks!!

[Victor Duarte]

hi kdog, i dont know whith tube you re talking about... but if it is a critical one, you should avoid sand , it is really too much abrasive, i remember when i was repairing a body part of my vintage car, i insisted with sand to eliminate some rust and... did a very nice hole ! have you considered soft abrasive paste with a slow-speed drill ?

sorry for i m not an aero engineer, just giving my proper experiences..

[KDOG]

I wasn't too sure about sanding to begin with, just thought I'd ask. I'm talking about the mast,keel, and tailboom....

[gyropilot]

I wasn't too sure about sanding to begin with, just thought I'd ask. I'm talking about the mast,keel, and tailboom....In preparing aluminum parts for treating and painting, I first use a Fine grit 2" diameter 3M Scotch-Brite Rol-Loc buffing disk on an air-powered angle-head die grinder. It makes quick work of this type job and leaves a beautiful swirled satin finish on the parts. Afterwards, I wash the parts with soap and water, and then chemically treat, prime, and usually paint (not always). Paint adheres well to the surface of parts buffed with Scotch-Brite and properly chemically treated.

The Scotch-Brite Rol-Loc disks come in the following grades identified by color:

Gray = Super Fine (http://www.use-enco.com/CGI/INSRIT?PMAKA=505-6251)

Blue = Fine (http://www.use-enco.com/CGI/INSRIT?PMAKA=505-6248)

Maroon = Medium (http://www.use-enco.com/CGI/INSRIT?PMAKA=505-6245)

Brown = Course (http://www.use-enco.com/CGI/INSRIT?PMAKA=505-6242)

These disks require a holder (http://www.use-enco.com/CGI/INSRIT?PMAKA=505-6258) (backing pad).

The blue / fine disks work best for all around surface buffing of aluminum. If you need to smooth sharp edges of parts, then the maroon / medium disk is best followed by the blue / fine disk. The brown / course disk is *very* abrasive and will rapidly remove aluminum leaving deep surface scratches behind, and thus should only be used for massive metal removal (like rounding corners on thick parts and sheared plates, etc.).

Locally, Harbor Freight Tools (http://www.harborfreight.com/) carries these products at a good price, but I couldn't find them in their website catalog. Enco (http://www.use-enco.com/) is a good low-priced online source.

Regards,

John L.

[KDOG]

THANKS!!! Great info... Now as far as chemically treating what do you use for that? And Do I need the the air powere die grinder? Can I do it by hand?

[Doug Riley]

As a cheap Yankee swamp rat instead of an award-winning craftsman like John L., I buy the green Scotch-Brite pads sold in the cleaning products section of the grocery store. Sometimes the store brand is a few cents cheaper still.

Don't sand the tubing unless it's necessary to remove a serious scratch (the kind that will catch your fingernail). Sanding tends to create new scratches and embeds grit in the metal surface that then forms new starting points for corrosion. This is even more true of steel wool, which is VERBOTEN on aluminum.

6061 re-corrodes within minutes of polishing, so don't bother cleaning it up until you've actually started your paint prep. Wear gloves when doing the final cleanup; the salt and oil from your skin play a big role in paint peeling.

[scottessex]

usually phosphoric acid, and then rinse, and then alodine, and rinse with water.
At your stage I wouldn't even bother with etching and treating until you are ready for paint.
But, you can use EAGLE ONE mag wheel cleaner, for uncoated aluminum wheels, it is a phosphoric acid in a spray bottle, works very well. Available at auto parts stores.

[KDOG]

Ok, what about the alodine?

Doug, from one Yankee swamp rat to another, do the green Scotch Brite "grocery store" pads work good? Any technique I should know about?

[Doug Riley]

KDOG, alodine is a good stabilizer. It is a chemical version of anodizing. It's also extremely toxic and a known carcinogen. Treat it accordingly.

Hand-polishing with Scotch-brite is tedious but do-able. Fold the pad up and scrub away. Polish the long way rather than across the grain of the extrusion. Don't touch the polished metal with ungloved hands. Watch for the very fine metal dust you'll kick up; a good dust mask is advisable. Your nose will run black goo if you don't use one. Gross.

[KDOG]

Cool. Where would I get the alodine?

I have the time to do it by hand. This isn't going to be a fast project. I see me working on these three extrusions for the better part of 3 weeks to a month... I could work some more overtime to get components quicker, but I'm already hurting myself working the overtime that I do now. So I don't think I should. My next purchase will be the angle package, hardware package, and cluster plates from starbee, which will be well over 300 bucks. I don't see getting that till the beginning of October.

[scottessex]

Aircraft Spruce, Or Wicks should have it, you might be able to get it locally, but I am not sure, with EPA restrictions and all.

[gyropilot]

Cool. Where would I get the alodine?Alumiprep 33 (http://www.loctiteaero.com/Images/Datasheet_PDF/hst_alumiprep33.pdf) is a phosphoric acid cleaner for aluminum.

Alodine 1201 (http://www.loctiteaero.com/Images/Datasheet_PDF/hst_alodine1201.pdf) is a chromic acid based conversion chemical that leaves a nice golden yellow finish sutable for painting.

Both are available from Aircraft-Spruce (http://www.aircraftspruce.com/catalog/cspages/alumprepaint.php).

Regards,

John L.

[KDOG]

Thanks, got the page bookmarked...

[RICK MARTIN]

John,
I'd like to know more about Alodine. Specifically, after using the alodine can the finish be left as is or does it have to be painted or finished in some other way?

[scottessex]

The alodine will provide some measure of corrosion protection.
But it will make your paint adhere much better, You can also get self etching epoxy primer that sticks like white on rice.

So: Etch the aluminum
alodine.
pimer.
paint.
then hope your bolt holes aren't too small after being filled in with primer and paint!

[KDOG]

The alodine will provide some measure of corrosion protection.


Can you put multiple coats of the alodine on and then leave it?

[RICK MARTIN]

John, Scott, Doug,

Thanks for the response on the Alodine. I'll assume that Alodine treated aluminum would be better than no finsih at all. Is there any harm in leaving it that way for the long run. My real concern is the inside of the tubes.
Now, why not use steel wool on aluminum as long as you work to a very fine grade and clean it up real good?

[Doug Riley]

Rick -- Just noticed your address. My in-laws live in Bradenton. They bragged for years that Bradenton never got hurricanes.

The Alodine surface is nice looking but pretty soft -- not like the very hard surface you get with electrically applied anodizing. You can scratch it with a fingernail. I think that it wouldn't hold up as a finish coat.

Steel wool sheds bits of hard metal fiber that work into the softer aluminum. You can't easily get them back out again... like slivers getting under your skin. They form the nucleii for corrosive pitting. Makes a mess after the metal gets wet a few times. If you insist on using metal wool, buy aluminum wool from one of the aircraft supply places.

[gyroman]

KDOG,

You may be able to find the 2 chemicals at your local auto paint store. Most auto parts stores are not going to carry it but some have extensive paint areas within. I found a local auto parts store that carries a wide variety of paints. They have basically the equivalent of alodine and alumiprep made by PPG. It was quite a bit less than purchasing from one of the online aircraft houses ( not to mention shipping) and I got almost twice as much....

[RICK MARTIN]

Doug,

Thanks. Those are the answers I was looking for. I have used steel wool all through my original build. I guess I havent really seen the effect yet as I have always kept the gyro in my garage. I'll look into the aluminum wool. I'm guessing since it must be softer, that it doesn't work quite as well or gets used up pretty quickly.