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  • Billet Aluminum refuses to polish...

    Hi Everyone,

    Been polishing stuff off and on a few years; mostly molds for products I make. Given that any visible imperfection in the mold transfers to every part made, I have become rather good at convincing aluminum to polish.

    But there is one mold section of my latest product that is the most ornery hunk of aluminum I have crossed paths with. Start being nice to it at all and it turns gray. It has some kind of material fallout akin to when I polished a cast mold, but much smaller. Initially, fallout happened with 1200 grit and also with any polishing buffing. I had the part re-tempered to T6 and that's helped a lot; and the aluminum grabs at sandpaper the way it should. It is billet and allegedly 6061 T6 with a certificate.

    I made a video before getting the part tempered: https://youtu.be/7AdXyMTEOks In it you can see the results of other parts of the mold as well as this part's refusal to be clear.

    Some observations:
    » Whenever the ambient temp drops, polishing becomes troublesome. Now I've got a heat lamp and halogens pointing at it when I work so the part is warm to the touch. This did make a difference and the idea came from reading threads on here.
    » It takes first cut really well, always making me think "this time" is going to be the one.
    » I have tried buffing (cutting) after block sanding to many different grits. I end up needing to re-sand to get out waves from polishing or the pitting that sometimes happens.
    » The metal seems to hate speed: run a buff up properly fast and those pesky little bits of grit will fallout leaving a pit and a healthy scratch next to it.
    » For cutting I have tried black, brown, and mother's billet. All are excellent at removing sanding marks. The exception is when I tried buffing after 600 grit instead of 2000 or 2500; after 600, the effort it takes to clear the sanding will make the gray haze start to show up.
    » After the heat treatment, using white compound (JacksonLea and a few others), stiffer buffs tend to dig in and instantly load up while the usual softer buffs just make gray happen.
    » I have gotten to to have zero buffing marks (perfect mirror finish) and the gray seemed ok ... until I walked outside. When dark is reflected, the mirror surface is visibly cloudy and quite ugly.
    » I use brake cleaner to remove any compound buildup between stages. I also use Argo corn starch with fresh cotton t-shirt on the surface until it comes away clean.
    » Using a loose buff always makes a combo of haze and undesired scratches. Using a flannel buff always makes gray.

    Things I've tried to remove the haze:
    1) Flitz (buff wheel and by hand),
    2) Mothers Billet, by hand and by buff
    3) Rubbing in the Argo like a mad man
    4) Novus plastic polish, (solutions 2 and 3).

    It looks like any time I'm "nice" to the surface, it grays up and I have to go back to brown or black compound at the first hint of hazing. Tomorrow, I'm getting some new stiff buffs and am going to try using blue compound (plastic) with a stiff buff to see if I can manage to minimize the remaining marks while also avoiding haze.

    Anyhow, thanks for reading. Not really expecting help, just kind of sharing my situation. I'll update with end results and technique.
    - Chris

  • #2
    Re: Billet Aluminum refuses to polish...

    Interesting results...

    I wet sanded 1200, 2000, 2500, and 3000 grits. I was pretty attentive to the 1200 and 2000 grits and made a passable effort at the 2500 then pretended to care with the 3000.

    After doing the inside of the mold, I went to the test patch on the outside of the mold and started experimenting. While I could cut with a sewn buff and semichrome, it hazed up pretty quickly.

    My plan from last night was to use plastic/blue compound and a treated sewn buff to cut then a sewn buff to color, and here's the result from 3 passes cut and 5 passes color:

    Click image for larger version

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    The swirls are from the buff and only show up with one angle of view. Working under halogens in otherwise dark shop makes very easy work of finding swirls and scratches. Odd angled scratches are from abusive application of corn starch with a not-perfectly-clean t-shirt section. Lighting is from 3 halogens on posts on opposing angles. Darkness is looking at the ceiling being reflected.


    Click image for larger version

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    Same lighting and position of part now with the reflection from a tree that's 50-odd feet away, outside the shop's roll-up door.


    If I can accomplish this on the inside of the mold tomorrow, I'll be very happy. The swirls are acceptable, there's outstanding color, and almost no haze. (next post, only 2 attachments per post).

    Comment


    • #3
      Re: Billet Aluminum refuses to polish...

      Click image for larger version

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      It took some work to find and capture the haze/clouding with the phone -- and like the swirls, only shows in a narrow angle of view. This appears acceptable to me... final judgement outside in the direct sun tomorrow with the reflection being the dark ceiling inside the shop.

      If it looks this good in the sun and I can manage this quality on the inside, I'll be very happy. While it is lower quality than I prefer, this option is acceptable and the alternative is $7-10k to get a new top piece CNC machined.



      Click image for larger version

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      These are the 2 buffs I used on the outside of the mold: a porter cable treated buff from Lowe's and a Harbor Freight sewn buff. Both were well used but thoroughly raked before this test to remove buildup. The blue compound I used is the stick in a plastic tube from ... Harbor Freight.


      I've got at least $100 in compounds from Dico, JacksonLea, Home Depot, and Lowe's. So for giggles, I chose the most accessible option first. I've got probably $200 in buffs from every source I can find. I like the Porter Cable buffs (from Lowe's) because they are well balanced, have the leather reinforcement on the center hole, and have proven quite durable. The Harbor Freight buffs hold up pretty well, too, and are cheap.


      If tomorrow goes well, I'll report back sometime before Monday... will be busy driving the mold to the plant and then taking a couple days off.

      Thanks,
      Chris

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      • #4
        Re: Billet Aluminum refuses to polish...

        Are you absolutely certain that there is no fine grit residing in your buffs?

        Richard

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        • #5
          Re: Billet Aluminum refuses to polish...

          Hi Richard,

          Yes -- I've purchased a number of new buffs. I keep buffs in bins with their compound and also have a "mixed up" bin that I banish contaminated buffs to.

          As it turns out, the "all blue" method came up with some outstanding results... I did the 2 steps mentioned above. And then I grabbed the loose flannel 6" buff that was in the blue bin to see what might happen. I ran it at full speed with barely any contact to the surface and I was able to not make more haze.

          Click image for larger version

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          Click image for larger version

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          I still had to be careful with the last buff as haze did try to crop up here or there, but not much and also limited to narrow viewing angle. Delivered the mold to the plant today, so I'm quite happy.

          Now it's beer:30.
          Chris

          Comment


          • #6
            Re: Billet Aluminum refuses to polish...

            Good work. I've come across some aluminum too that just doesn't want to act right and get polished. I'm fortunate though. Most of my aluminum sculpture pieces are beat out of .050 1100 sheet metal. That stuff just loves to take a shine.

            Richard

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