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Thread: Why do we use 6061?

  1. #1
    Insider PBSteve's Avatar
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    Why do we use 6061?

    From a discussion on PBN

    Quote Originally Posted by got wake?
    Please explain why you think it is so expensive to 3D mill 7075.... I'm an applications engineer for one of the best cutting tool manufacturers and have 3D milled a lot of 7075, btw. The time consuming part comes from smoothing everything out, since 6061 will tumble the tool marks out faster, but if the proper media is used, 7075 isn't bad. I used media for my stainless parts with 7075, and it worked well.
    Quote Originally Posted by Umami View Post
    Interesting. I was under the impression the brittleness of 7075 made it more difficult to machine (harder), but that doesn't seem to be the case. It seems the hardness and brittleness means smaller chips, which makes it easier to machine.

    I do know 7075 definitely doesn't take type II ano well, though.

    Shoot me a PM if you want to keep the discussion going, I don't want to derail the thread.
    I got this from a couple forums. I was definitely under the impression that 7075 was more difficult to machine, but based on this guy's comment and some wandering around on practicalmachinist.com, that doesn't seem to be the case.

    6061 will get gummy and most likely you will have to drop your rpm. 7075 has a great short chip formation where 6061 will string much worse. The stability is decent in most cases in billet, but in forgings or castings it is more part dependent.
    http://www.practicalmachinist.com/vb...-6061-a-95307/

    (I like those forums, experience on the ground is great)

    Regarding anodizing, I already knew 6061 had better ano properties but I got confirmation of that here:

    Actually 6061 will respond nearly identical to 7075 with Hard anodize. The difference is with type II anodize. Where 7075 will not take the colors as well as 6061 will. And 7075 has to be run through a desmut first before type II can be performed.

    The biggest difference you will see is surface finish matching. If the bead blast is not the same on two different parts the black anodize will only make the contrast worse.
    http://www.calguns.net/calgunforum/s...php?p=11562020

    7075 is also considerably more expensive, about 50%. That combined with the anodizing properties seems like enough to keep people away... perhaps there's something else out there people haven't considered?
    Ever so many citizens of this republic think they ought to believe that the Universe is a monarchy, and therefore they are always at odds with the republic. -Alan Watts

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  2. #2
    Insider ElPanda's Avatar
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    cost is the deciding factor

    there is no reason to switch from 6061 when it fits perfectly in most paintball applications

    now if there were an actual strength requirement where you would be better off using 7075 that would be a design exception

    from a business perspective it simply makes no sense to use a more expensive material when you end up with an identical part for a significant decrease in cost of the material

    if you are comparing it to 7075, yes it is softer, but to say you have to start affecting speeds and feeds for every tool, I totally disagree

    I have extensive experience machining both and I use identical speeds and feeds for both, and they both machine beautifully (7075 more-so because it does indeed break chips a little better due to the decrease in ductility)
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    Insider Dayspring's Avatar
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    So, say, you'd use 6061 for a ULE body for the Automag, but 7075 for the valve due to pressure?

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    Insider PBSteve's Avatar
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    If you're going to rebuild an automag, just build the valve so you don't need the insane pressures and don't bother with SS or 7075

    In the Paragon we use some 7075 for small bits that require the strength, but we don't want to go to stainless because of weight considerations.

    Regarding the cost thing that is definitely the driving factor. But is there anything else available of similar properties and cost to 6061 that people overlook? I'm not particularly aware of the available alloys... should probably spend some time on MatWeb, but if anyone has suggestions I'd love to hear them.
    Last edited by PBSteve; 10-20-2014 at 08:41 PM.
    Ever so many citizens of this republic think they ought to believe that the Universe is a monarchy, and therefore they are always at odds with the republic. -Alan Watts

    I work for the company building the Paragon

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    Insider PBSteve's Avatar
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    Bummer, 6013 is a small fortune and limited in availability.

    Guess we'll be using 6061 for a while.
    Ever so many citizens of this republic think they ought to believe that the Universe is a monarchy, and therefore they are always at odds with the republic. -Alan Watts

    I work for the company building the Paragon

  7. #7
    I think a lot has to to do with the ability of 6061 taking to anno better than 7075. But this is a pure guess. A professional annodizer would have to chime in that. But what about this, i know that the SP shockers used something other than 6061 fir the SFTs, but would wear anno off easily. What was their aluminium grade?

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    Insider new ion?'s Avatar
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    2000 series. Andy can tell you more.. I know he's mentioned more than once it was actually harder to machine.

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    Spent years 3d machining 7075 AGD Sluggo bodies and 6063(?) AGD rails. To me, they both cut about the same. The 7075 seemd to come off the mill "cleaner" but that could have been a coolant staining issue. 7075 is expensive and overkill for anything aesthetic, but it was Tom's wish to overkill things. Anodizing took a few times for the local guys to get them close to matching colors, but once it was dialed in it wasn't really an issue.

  10. #10
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    The reason for 6061 is like 90% cost-based and like 10% material properties. It's good ole fashioned economies-of-scale leading it to be the cheapest due to high demand. So long as it works in the application there's no reason to spend any more with a different material, unless you need the rigidity of a 7000 alloy.

    Shockers were 2011. Significantly faster and more reliable to machine, but the anodizing was hit-or-miss.

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