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How smooth is too smooth?

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  • How smooth is too smooth?

    I'm curious as to what the optimum finish on an aluminum surface should be that will ensure a powder coat will hold the best? Say you have a cast aluminum part that you plan on powder coating, but you want the part to have a nice, even, "slick" appearance so you decide to sand down the cast. At what grade of sandpaper would you stop the sanding process? If something has been show polished, will it need to be roughed up before coating? Any help would be appreciated.
    "Some people are like sandpaper: they may delight in the misery they inflict by rubbing up against you, but in the end you will come out smooth and polished while they'll just be ugly, wrinkled, and used up." - Beyonce Knowles

  • #2
    If it's been "show-polished"... a media blast with black oxide to modify the surface profile will be MORE than enough to accomplish your goals. If it's a bare cast aluminum (we'll say an intake manifold for example... I always use that). Just take and knock off the casting flash if there is any, and most high-spots with a file of some sort. Sand paper isn't really going to do squat for you in this case. All of the "low" spots should be filled in with the Caswell Lab Metal ( found on the openeing page when you enter this site at time of reply) and then evened out. Just media blast entire surface after that to assure good adhesion. At this point, you may also use PROD ALCHROM880 for a good chemical bond on aluminum. Coat as normal and all will be fine. Powder coatings have this wonderful "hi-build" effect which makes them such an attractive thing for the hobbyist (and machinist to request) to use. They hide the sins, in plain English. Even more-so when you put a clear coat on top! (click on the sticky forum in here that has pictures and you'll see how amazing some of the people in here have achieved these same results!.... very proud of you all). What you will end up with is a smooth "glassy" appearance that has hidden a great deal of casting marks, scrapes,chips and the like. Hope that helps......Russ

    p.s.- can somebody post the links to the Lab Metal and Alchrome880 for me? I'd give you the official non-stick thumb's up for the day if you could and I'm sure "thesound" would be eternally grateful for it as well. Thanks

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    • #3
      Sanding takes way too much time, in my opinion. Powders are good at hiding small imperfections because they are typically applied thicker, where as liquid coatings are applied thinner. Also when curing, the powder flows out and self levels, which helps to fill in moderate scratches. If you are working with cast aluminum, say a intake manifold, i would pick up some 80 grit greaseless compound and spiral sewn wheels. They cut much faster than paper and can be used in a drill with a mandrel....thus saving your arm from falling off. You might also want to pick up some felt bobs to use with the greaseless, and some sanding rolls/tapers. With these products, you should be able to knock down casting quickly. After you've gone through this, give it a quick thorough blasting with with a bead or oxide, or whatever you happen to use. This will remove residual greasless compound and other surface contaminents from handling it and what have you. From there continue with the rest of your powder coating process and you will get a nice, seemless, slick look. Good luck.

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      • #4
        or like russ said, you can build UP and fill casting marks in.

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        • #5
          http://www.caswellplating.com/aids/metal.htm

          heh. thumbs up to me for remembering :P

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          • #6
            Lab Metal - http://www.caswellplating.com/aids/labmetal.html
            --
            Mike Caswell
            Caswell Inc
            http://www.caswellplating.com
            Need Support? Visit our online support section at http://support.caswellplating.com

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            • #7
              Wow, you guys are awesome. Thanks for the info; much obliged. And you had both guessed correctly: I'm working on an LT1 intake manifold. The reason I'm looking into powder coating it are for two reasons. (1) Because the casting of this manifold leaves MUCH to be desired. In the process of sanding it down I ran into many areas where air bubbles in the casting surfaced. More sanding only yielded,(you guessed it), more air bubbles. (2) I had considered having this thing triple chrome plated, but the more I think about how much copper will need to be applied to fill in the air pockets, the more I think this manifold would get hot enough to boil liquid nitrogen at the North Pole in the middle of February. So I think I'm gonna bite the bullet and purchase some of that Lab-Metal Putty to fill in the air bubbles, then get some of that Reflectra Chrome stuff and go to town. I'll be sure to upload some pics of the finished product when it's complete. Thanks again guys.
              "Some people are like sandpaper: they may delight in the misery they inflict by rubbing up against you, but in the end you will come out smooth and polished while they'll just be ugly, wrinkled, and used up." - Beyonce Knowles

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              • #8
                Big thanks to Caswell for posting the link. You get the official non-stick "good guy" award for the day. Street value is nothing, but it makes for happy coaters .

                Anyways.... I'm glad you found our advice helpful to you. You have no clue how many uses you are going to find for lab metal. Heed my warning though.... it's as tough as all get out so go easy on it. ( I know I covered this EXACT process in Tips and Tricks somewhere already,lol) It's like bondo on steroids. Go easy and all will be fine. Oh yeah.... WE WANT PICTURES when you are done,lol. (sorry... I love when you guys post pics....so shoot me) If there's anything else that any of us can help you with, don't hesitate to ask. Unlike *cough* other places.... we like to help each other ....... Russ

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                • #9
                  Just wanted to mention that you will want to also pick up some of the clear powder to put over the reflectra chrome. If you don't it will tarnish on you in no time. I would hate for you to go through all that work and it end up a dull grey
                  Good luck and yep, we want to see some pics

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