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Finishing prior to anodizing

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  • Finishing prior to anodizing

    I machine a lot of 6063 aluminium parts on VMC. These are later anodized semi-bright black. I manually sand paper them to remove the machining marks which takes lot of time. I would like to know other fast process to remove machining marks. Someone suggested me glass beads. Please let me know how to use glass beads and what should be the grain size?

  • #2
    Re: Finishing prior to anodizing

    glass beads will give a very dull finish, you should look into vibratory polishers, its the easiest way
    "A stupid man's report of what a clever man says is never accurate because he unconsciously translates what he hears into something he can understand.
    Custom Anodising

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    • #3
      Re: Finishing prior to anodizing

      To add to spankey's post, if you're looking to remove machining marks, you're going to be left with a dull finish no matter what you use.

      That said, I highly recommend a vibratory tumbler. I use a Thumler and it runs almost 24-7 and has been doing so for years without a hiccup.

      I keep two bowls for the tumbler. One contains polishing media (walnut shells treated with chromium oxide). The other bowl contains abrasive media to remove machining marks or deep scratches (plastic media).

      For most of my parts I'm able to run them in just the polishing media prior to anodize and they come out with a nice mirror shine. These parts are machined to a 0.8 ra finish so come off the machine pretty smooth. However, when I come accross a part that has undesireable scratches or deeper machining marks, I know I will have to run it in the abrasive media first, as polishing it will only make those defects nice and shiny, not get rid of them.

      The abrasive tumbling process only requires a couple hrs to get rid of most machining marks. The part will be very dull. I normally give the parts a quick dip in lye after this step to clean off the surface as they tend to get dirty when abrasive tumbling. Then the parts go into the polishing media for several days to get polished back up. Yes, this requires time, but depending upon the size of the part and the size of your bowl, you may be able to do a lot of parts at once, freeing up your time for more important things.

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      • #4
        Re: Finishing prior to anodizing

        I do the same as g8erh8er!

        I use synthetic 3/8" cone media for about 8 hours then switch to treated cob for another 12 hours in my vib finisher.

        I'm in the process of designing and building a high energy barrel finisher at the moment which will cut the whole process by 2/3 time.

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        • #5
          Re: Finishing prior to anodizing

          Thanks. Could you please give me more information of the process such as how does tumbler behave on sharp edges, what should be size of tumbler for big parts, how much time one cycle of tumbling takes?

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          • #6
            Re: Finishing prior to anodizing

            Vib finishers take care of sharp edges nicely, depending on the type of media of course. As a rule you usually start with a med to heavy cutting media in the beginning like synthetic or porcelain. I like synthetic because all you have to add is water, no detergents or other specialty liquids.

            As for size of machine you want one with enough size to allow your part (or parts) to move freely through the media. I built my system around the size of parts I normally make which are 5" dia x .875" wide with very intricate mill work in them. The style I choose was a vibratory tub as opposed to a bowl due to the size and shape my parts. Each part sits in it's own chamber so other parts don't impinge each other. Cycle time for the synthetic media is usually 6-8 hours and the treated cob to shine them up runs for 8 to 12 hours.

            Here's a pic of a reel I finished the other day to give you an idea of finish. You can achieve even better finish if you take more time.

            Click image for larger version

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            • #7
              Re: Finishing prior to anodizing

              Very nice gardinhackle! I never had any luck with cob media, just didn't get the parts as shiny as walnut shells do. Are you using one of the rotary tumblers that allow you to put several barrels inline? Always wondered how those work compared to a vibe tumbler.

              To the OP, we really need to know what size parts you're looking to do to give you a better recommendation. Also, how much $$ you're willing to spend.

              Tumblers can be cheap, or very expensive. I bought the largest version Thumler makes and I think it was around $500 at the time. It allows me to tumble 30-50 small parts at a time comfortably. I could probably fit more, but then I would get more part-to-part contact and you end up with dings/scratches.

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              • #8
                Re: Finishing prior to anodizing

                Originally posted by g8erh8er View Post
                I never had any luck with cob media, just didn't get the parts as shiny as walnut shells do. Are you using one of the rotary tumblers that allow you to put several barrels inline? Always wondered how those work compared to a vibe tumbler.
                Thanks g8erh8ter!

                I use the treated cob sold by McMaster Carr. It works well. I have untreated walnut that I added white rouge to but it doesn't seem to work (at least for me). My vib finisher is a "U" shaped tub style but it's far too slow. So I'm working on building a high energy barrel finisher (as you mention) that has 4 barrels on the drum. I'm building mine with only 2 though as I don't require one that big. The centrifugal force it imparts on the parts is tremendous causing the media to work more efficiently and much faster. One negative point about vib finishers is they take too long to do the insides of the parts if at all. The Barrel finisher will do it because it compresses the media into every part of the component.

                Same concept as the one in the video but scaled down https://www.youtube.com/watch?v=WhFC9hTCdRA

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                • #9
                  I use plastic tumbling media (the green colour) plastic media that you can find on Amazon, Habor Freight or any mass finishing supplier
                  The pyramid shape media is a good choice if your parts have special surface geometry.
                  Our purpose is to find the right size and shape media that can finish the surface of the entire part
                  At the same time, media will not get lodged in the hole of the part even after long time use (when they become smaller and smaller)
                  You can read the article to understand more how to choose the right tumbling media

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