AR-15 lower failure, new spools.

Decided to go the cheap route and get an AR-15 lower with a .22LR upper, so I could put several thousand rounds downrange for a fraction of the cost of 7.62 ammo(as my AR-10 would use).  Here it is, fully assembled.

IMG 0112

Got all the parts needed to build the rifle for under $400, had a printed lower, and was all ready to go out to the range, when I bumped the buttstock with my elbow and tore the receiver apart.

IMG 0122

I had used epoxy putty to put threads into the buffer mount of my printed lower because the threads as printed were too tight and the part fractured under the stress of inserting the buffer tube.  This fracture and the decreased holding force from epoxy putty(compared to printed threads) contributed to the failure.

But I had a clever idea.  I’m going to print the lower receiver in two parts.  The buffer tube threads in one part, along with the rear mounting lug, and then the rest of the lower as a seperate part.  This seperation will allow me to use very high detail on the threads, and orient the lower receiver in such a way that it won’t need support material.

I have been wrestling with hot-end issues on my printer and installing the new filament spools.

IMG 0120

That’s right. Two 10 pound rolls. Won’t be long before I’ve got a pair of empty spools.  When my dual extruder shows i’ll be all set to rock the two-color prints.

 

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6 Responses to AR-15 lower failure, new spools.

  1. Have Blue says:

    Bummer about the broken buffer tower! I’m not sure how long mine will actually hold up, as testing with a .223 upper is showing a bit of flex, and I really need to reinforce that area more. I came across a new polymer upper the other day, and noted that it appears to have material all the way around the buffer tower (not to metion integral trigger guard and larger front takedown lugs): http://www.thefirearmblog.com/blog/2012/07/13/ati-omni-lower-50-polymer/

    I really like the idea of printing the buffer tower as a separate piece – getting proper threads to print will probably be one of the trickiest areas, and being able to dial in your settings for that without needing to print the rest of the receiver will be very nice. Can’t wait to see what you come up with for that!

    • turomar says:

      Congrats on the .223! I saw your post on AR15.com
      Someone linked to it on SomethingAwful, where i posted about my broken lower(cuz it was kind of awful).

      I appreciate the nice things you said about me, though I admit now I feel more pressure to get my AR working.

      • Have Blue says:

        Well, I wouldn’t feel any pressure – it took me over a year to finally get off my butt and test fire my lower, after all!

        At any rate, your work has been fantastic, as it shows what is possible with the current generation of open source printers. Additionally, the issues you’ve run into (warping, weak buffer tower, etc.) will be far more useful to other RepRap/Makerbot users than my experience of “eh, it worked for me”.

  2. C. Wells says:

    Hi Have Blue,

    I’m a reporter trying to get an accurate story on how you constructed the .223. Is there a way I might be able to contact you with a couple questions?

    Thanks

    • AdmiralFDG says:

      You would probably have better luck contacting him through his site, but that appears to be melting from slashdot effect (I’m expecting similar any time now on this one)

      -AdmiralFDG
      Site Admin

    • Have Blue says:

      Charlie – I dropped you line via my gmail account. I’ll see if I might be able to give you a call tomorrow.

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