Monday, September 18, 2017

Turning Aluminum Cans into an AR Lower

There are few 20 minutes videos that I've watched that haven't had me reaching to see if I could skip over some nonsense.  This one had my complete attention for all 19 minutes.  Farmcraft101 takes five pounds of saved aluminum cans and recycles them by melting and casting an AR-15 lower.  H/T to ENDO for the link.


I've got to say his PPE (personal protection equipment) made me cringe a little, but that's the only thing I can be critical of.  Upper arm-length, heavy, leather gloves combined with shorts and bare legs while pouring molten metal is enough to make me cringe.  The rest of it is great stuff to know.

That said, I have to wonder if the metal would be useful for most things.  When you see things saying they're made from "Aircraft Aluminum" or an alloy like 6061-T6 or 7075, that's a specific composition of alloying elements in specific proportions, and T6 is a specific heat treatment.  If I took a pound of 6061-T6 cutoffs and melted those down, instead of soda cans, I wouldn't end up with 6061-T6.  All metals are like this, really.  Steel, brass, aluminum, titanium or whatever, the properties you see depend on the ingredients (alloy) and how they're treated.  Anyone who has taken the mechanical engineering classes on materials has seen something like this iron/carbon phase diagram.  The different colors code for different microstructures in the steel, the temperatures and concentrations of carbon that lead to their formations.  There are similar curves for aluminum and its main alloying additions - silicon and magnesium in 6061 or zinc and magnesium in 7075, for example.

That said, an AR lower has got to be pretty non-critical.  It's not just that plastic lowers are a thing, and can be bought in any quantity from an handful of companies, there's that guy who made one from HDPE - the plastic used to make kitchen cutting boards.  If a cutting board works, it's probably not a high-stress application. 


10 comments:

  1. I once read somewhere that you cannot use aluminum cans because the inside is coated with plastic. But I guess if it all burns away and does not leave any contaminants behind then you have a ready available supply of aluminum. That's a lot of detailed milling work, I'd still rather buy an unfinished lower for eighty bucks and finish it with one drill hole...

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  2. The stress point is at the radius where the threaded boss for the receiver extension curves into the top of the lower. The upper hits that boss during recoil.

    We've encountered cracks there casting lowers from 2-part resins. The company that sold us the molds now offers a stainless steel frame to reinforce this area that's embedded in the plastic.

    But, no, it doesn't need to be super strong to survive firing.

    Soda can aluminum is about half as strong as 7075-T6 in about every particular. The real question is, does it matter that much?

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    1. It might be one of those situations where, if they were free to change the shapes around there, they could redesign that with thicker plastic and not reinforce it. They probably can't do change the design because it will make the mating parts not fit.

      Embedding some metal in the plastic sounds like an easy way to reinforce it.

      Some aluminum alloys machine like stale chewing gum. They stick to the cutting tool and gum up the cutter. On top of that, the part you've machined isn't very strong.

      The Aluminum Association says cans are 3004 alloy. I looked it up here and it looks like a stronger alloy than 6061. I'm shocked.

      And, Mike, it's a bit more involved than drilling a few holes, but, yeah, this is just a project that's neat to do to show it can be done.

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    2. "Embedding some metal in the plastic sounds like an easy way to reinforce it."

      Good comment, especially as I think Glock has pretty much proven that to be true.

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    3. I believe beryllium or some other metal is added specifically to make it stretchy, so that the can shape can be stomped out at ridiculously high speed and result in uniform thickness and no tearing. Can metal is not a "normal" alloy, it was designed for one unique purpose.

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  3. And instead of a bought for the purpose broaching setup, he makes one from drill rod.

    I will have to watch the expanded series of videos.

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  4. My friend John Jay, over at the Summer Patriot, Winter Soldier blog ( http://wintersoldier2008.typepad.com/ ) made a lower out of laminated hardwood, stainless steel sheet, and PVC pipe. We had many online discussions as to manufacturing it. While it may not be as pretty as an LMT, it shot and functioned pretty well. This was done to illustrate the futility of gun ban laws.
    John doesn't have a whole lot of features to find stuff on his site, but HogNose at WeaponsMan cataloged the progress on the build.
    http://weaponsman.com/?p=25473

    I've seen lowers made from multiple pieces of laminated steel, welded together - to pieces of aluminum bar stock screwed together. I have even held some pretty cheesy injection-molded, plastic ones as well. As long as everything lines up and goes bang.....well, you know.

    Leigh
    Whitehall, NY

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    1. Great stuff. To me, one of the whole points of this is the futility of gun ban laws. It's all basically old tech. The machine tools are 150 years old, but guns have been made for much longer than that.

      There are plans online for an AR lower made from thin aluminum plates held together with hardware. I think it could be made with a hacksaw, some files, maybe drill and taps. McThag as made a few from the cast resin and molds that are on the market.

      As the saying goes, the banners "can't stop the signal".

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  5. And now we have an integrally suppressed, black powder rifle that avoids all of the onerous laws. Available over the internet and shipped to your door, now tax, no 4473, no prints. https://www.store.silencerco.com/products/maxim-50

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