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Thread: metal prep

  1. #1

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    metal prep

    I have a few steel parts for my plane (hinges, eyebolts, controls, etc...), how do you recommend preparing them before install? Should the aircraft spruce eyebolts with cadmium coating be cleaned, primed, and painted? Or just the sheet metal that I create parts out of? What specific chemicals and where can I find them (including type of paint that is appropriate). What about my aluminum gas tank? Does it need to be treated in anyway? The aluminum cowling?

    Thank you

  2. #2

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    Find the local auto parts outlet that sells real paint to the autobody shops in your area. They will sell you good primer for steel and for aluminum. Modern primers will grab onto a clean, scuffed up surface without any problems.

    The top coats depend on what your spray gear is. If you have a place where can spray polyurethan safely, you can buy an entry level HVLP set up and produce great results. OR perhaps your local EAA chapter has the gear and you can use it.

    There is no magic, just takes practice. Never thought that I would own 8000 grit sand paper. My wonderful wife says that my fuel tank is the best looking one that no one will ever see. And a fuel tanks is a great part to start learning to spray on for that very reason.

    Remember to use breathing protection. Polyurethane paint will kill you in short order if you breath the overspray.

    EAA publishes lots of good info on how to do this. And my local auto paint supplier is happy to explain stuff.

    Aircraft painting in 2012 is no different than painting a truck or car. The technology has converged.

    Best of luck,

    Wes

  3. #3

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    I'd suggest not painting anything that is already cadmium plated (clear cad or dichromate dipped cad) as that already has pretty good corrosion resistance.

    Zinc though is something else and commercial & consumer stuff is much more likely to be zinc plated - and some zinc maybe even dichromate dipped (the yellow tint) stuff).

  4. #4

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    It is common practice to prime and paint cad plated bolts. The cad plating actually is a good base for the primer. No additional prep really needed. Just make sure that they are clean of any grease or oil.

    Go take a look at any production aircraft and you will see all of the AN bolts painted by the factory (Cessna-Piper-Mooney-Gulfstream...).

    Best of luck,

    Wes
    N78PS

  5. #5

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    Quote Originally Posted by WLIU View Post
    It is common practice to prime and paint cad plated bolts. The cad plating actually is a good base for the primer. No additional prep really needed. Just make sure that they are clean of any grease or oil.

    Go take a look at any production aircraft and you will see all of the AN bolts painted by the factory (Cessna-Piper-Mooney-Gulfstream...).
    I admit it is easier that way but it seems to me (i. e. paint after assembly) as it is the "dip it & ship it" approach!

    Paint in phillips screw heads is a bitch to remove.

  6. #6

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    Uh, If there is so much paint in a phillips screw head that it interferes with your screw driver, you aren't applying the paint correctly. Paint film thickness on an airplane is normally measured in thousanths of an inch.....

    Best of luck,

    Wes
    N78PS

  7. #7

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    Quote Originally Posted by idamon View Post
    I have a few steel parts for my plane (hinges, eyebolts, controls, etc...), how do you recommend preparing them before install? Should the aircraft spruce eyebolts with cadmium coating be cleaned, primed, and painted? Or just the sheet metal that I create parts out of? What specific chemicals and where can I find them (including type of paint that is appropriate). What about my aluminum gas tank? Does it need to be treated in anyway? The aluminum cowling?
    The only reason to paint plated hardware before installation is to match the existing finish. Airplanes are finish painted fully assembled so of course any exposed hardware gets painted at that time. I try to do the same whenever possible, it's just not practical for one or two fasteners. As far as other parts, there's a plethora of prep and finish products. Acid cleaners, self etching primers, finish primers, alodyne, finish coatings, etc. Each has it's application. Carefully read the handling instructions for any product you plan to use. Some of that stuff can kill you or worse.

  8. #8
    Eric Witherspoon's Avatar
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    What type of airplane?
    Where will it be stored?
    Which Al is it made of?
    How long do you want/need the airplane to last?
    What's the overall budget for the project?

    Question 1, because some designs/designers recommend that paint isn't necessary.
    Question 2, because if it's in a hangar, particularly in a dry climate, it could sit forever and paint would make no difference.
    Question 3, because if it's a 6061-based design, this is the same Al as is used in boats (often uncoated). Sure, if it's exposed to liquid water regularly, and that liquid water is allowed to sit, bad things will happen. But 6061 is more corrosion resistant (throughout the material) than 2024 Alclads. Sure, the clad might be more corrosion resistant on its own, but it's the thousands of rivet holes exposing the parent material in 2024 that can cause problems.
    Question 4 - if it's a largely 6061 airplane, there's lots of these flying around with no coatings whatsoever. They last "long enough" for their builders/owners to get what they want out of them - call it 20-30 years. Sure, there's some older homebuilts out there, but you'd probably want to be checking things out (getting into a restoration) by then. Then again, you may be looking for recommendations on how to build a monument to material protection technologies, that will still be sitting in a museum, looking new, 10,000 years from now.
    Question 5 - if it's an ultralight where you only have $5k in it, including engine, it's probably not worth piling in any more costs. If it's a $100k+ "dream of a lifetime" project - the ultimate and final airplane you will ever build, fly, or own, then by all means research the ultimate and go for it. If it's somewhere in between, the answer varies all the way from don't worry about it, just bolt it together to thou shalt epoxy prime every possible surface.

    Then there's alodines, anodizes, etc....
    Murphy's 13th: Every solution breeds new problems...

    http://www.spoonworld.com

  9. #9

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    Apr 2012
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    Taylor monoplane
    Stored indoors, not climate controlled, but in texas which has a very dry climate.
    Aluminum is only for the gas tank and cowling. I believe I have 6061 for the tank. Have not ordered the cowling Al. Which is best?
    Hope for it to last forever.
    Overall budget is growing as I age and decrease in debt, but trying to do it bottom dollar but safe and with longevity... so far I've put in about 3k... I have the empennage, wing ribs, landing gear, instruments, majority of wood expected for completion including ply, steel for hinges and things, aluminum for tank, fiber glass windshield, randolph epoxy varnish, t88 glue, all tools necessary. I expect to put in 5k for the engine, direct drive 69 hp from great plains. Unknown k$ for fabric covering of entire plane. 1k for misc. I do not expect the metal prep be a significant part of my budget because there are so few. Just some eyebolts, aileron and elevator and flap hinges, control stick, pedals, landing gear, gas tank, cowling, motor and mount of course, and some steel cables which I will grease up. I assume that the motor is to be untouched including bolts, the mounts need to be primed and painted, eye bolts with cadmium plating can be left alone or primed if desired (same for washers), 4130 hinges need to be primed and painted, aluminum cowling and gas tank should be left alone, landing gear left alone (greased per specs). Am I off anywhere? What primer and paint do you suggest for such few parts.

    What about the castle nuts? And the pins that secure them? What about the wire used for safety wiring engine bolts?
    What fabric do you suggest to go with the randolph epoxy varnish and about how much should I expect to spend?

    Thank you very much

  10. #10

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    Don't paint cotter pins or safety wire - it will hide any fatigue or problems with them.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

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