Monday, November 19, 2012

Building the 0% AR15 forging

In this nice little world we live in, there are two types of things that matter.
1. Guns
2. Everything else.

Well, to our friends at the BATFE, that's how it's all grouped, and there's a lot of stuff under the "Guns" portion that we here at this blog are interested in. Likewise, there's lots under the "Everything else" header that pertains to this blog. I know what you're thinking, what on earth is this redneck babbling about, and why should I care?
Keep reading. We're getting there.

Repeat visitors to this blog may have read a time or two that I've mentioned something being "80%" done, or an 80% kit, etc. This generally means is in reference to the BATFE's ruling that a gun ain't a gun if it ain't up to the 80% completed mark. The 80% that matters isn't just the whole receiver, but the parts that make it accept a bolt, a magazine, and a trigger group. You can drill holes in a block of aluminum until it turns to dust, but it ain't a gun until it accepts all of the above.
Now, go back to what I said up top......
It either is a gun, or it ain't.

This is a gun.



This is not a gun.









If THAT ain't a gun, then this damn sure ain't a gun, either.



Now, what does all of this have to do with this blog post?

Simple. A while back at the beginning of the year, I bought a bunch of the 0% AR15 forgings as shown in the last picture there. There is not a single bit of machine work done to these prior to you buying one, it's the same forging that almost every AR manufacturer in the US uses. Yeah, I know, so many of them claim they build their own proprietary design on their in-house CNC machines.
They don't.
They buy these forgings, pop 'em in their CNC machine, and carve out all the important parts.
Now, some places DO build their own from the ground up, but they are usually cut from a billet of auminum, aka a big chunk of raw 7075 aluminum. There's no real advantage to one over the other, in my opinion, having fired both in several calibers.
The aluminum could not be reached for comment, either.

So, we've established that we have some castings, and that they are not guns. What do we do next?
Well, as I've been doing with raw materials since I started this blog, we turn raw materials into guns!

Full instructions on how to machine one of these castings into a firearm can be found over at Ray-Vin's site here.
I machined a couple using those plans, and while it worked great, it took a long time because of all the set up work in order to machine everything perfectly.
Enter into the picture a company called CNCGUNS, who makes a jig for holding 80% AR lowers while you finish machining them. This jig appealed to me, and even though many people advise against using it on the 0% forgings, I had to try one out.
I borrowed my jig from another homebuilder a bit back, and found out why no one uses 'em to machine the 0% forgings. You have to have the top surface of the forging completely milled to spec before you can align the jig to the receiver. Okay, no big deal, it's gotta be done anyway, right?
So, here is a forging with the "deck" machined.
 Notice that there is no other machining done other than the top and buffer are being milled free of forging flash, and the front pivot pin is drilled.
(Yes, I wear latex gloves when doing machine work. I hate getting metal slivers in my hands, and the nature of my job demands that my hands stay as oil and grease free as possible.)

Now, we can align our forging into a CNCGUNS jig.


Using a flat surface, align the top of the forging with the top of the jig, and the rear of the buffer tube area with the back of the jig.
Normally, the CNCGuns jig is only used to hold the jig in place while the FCG pocket is milled out, and the corresponding holes are drilled in the side. This is a side benefit of the jig, as I will indeed use it to do that. Having the holes for the trigger, hammer, safety, takedown pins, etc. already lined up is very, very nice and saves a LOT of setup time (as in hours of time, not minutes).
What else do I do with this jig?
Well, I can now within a matter of seconds have my forging completely aligned square to the milling table, so drilling and boring the buffer tube hole no longer takes half an hour to set up and align. I can also mill the bottom side of the forging, where the trigger guard goes, and the pistol grip area. These areas used to require a specialized jig I machined, and the forging had to be precisely clamped to a series of fixtures so each area could be properly machined.
After all, the only thing about the AR forgings that does not get milled is the side profile. Everything else gets milled to size.

One thing that was taking a very long time to setup and perform the machine work on was the magazine well and the FCG pocket. There are several holes that must be very accurately drilled to remove a good bit of material before any milling takes place, and it requires the forging to be accurately setup. Once setup, the holes must be drilled out carefully, as you are drilling them with a long 1/8" drill bit. Any excess pressure on the bit causes it to flex, ruining the hole and making the bit wander off center.
I figured out that I could make my own jig that bolts to the CNCGuns jig, and has all of the important holes already laid out, and it holds the drill bit perfectly straight while I drill. 
Using a piece of 6061 1x3 aluminum billet, I laid out where each hole needed to be, then drilled it on my milling machine.
The jig after being bolted on top of the CNCGuns jig......

The forging after the drilling jig was removed......



The forging after the holes were all drilled to their final size prior to milling....


The magazine well is now milled out, as is the FCG pocket. All that remains is the milling for the small pocket that houses the take-down pin, and as you can see, those holes are already drilled.


Once I have those pockets machined and sanded smooth, I move on to drilling the buffer tube hole and tapping it with a tap I made a while back, then I drill all the necessary holes in the receiver and finish milling everything on the outside of the receiver.
All that remains is to file and sand on the magazine well until a magazine fits, then mill the bolt hold open slot (I forgot to do that when milling the mag well) and drill the hole for the buffer detent pin.

Not bad for a 20 dollar paperweight, eh?



That's my latest project, and while this particular receiver is actually for a .45 acp carbine I'm building, I have a couple more posts coming up on this same subject.
And for those of you following along about certain drum related items, yes, I know you want me to finish the drums. For what it's worth, the drum is on a welding jig with a newly made magazine, ready for assembly and testing. That's my next build post.....

Anyway, hope you enjoyed the AR forging post.
More as I get to it........

13 comments:

  1. Dang right I enjoyed it!

    The lower I bought had the mag well broached. In reality, I assume that means they cut out most of the metal with a drill or mill (or both) and used the broach to square the corners. Nice to have the square corners, but the 80% lower cost $80. Take a look - it will seem familiar!

    http://www.colfaxtactical.com/ar15.htm

    (And they've raised their price to $109! Ouch!)

    Lately, I've been thinking about making another. ARs are like potato chips, you know, you just can't stop at one. And besides, "Why do you need another one? Because DIANE FEINSTEIN, that's why." Maybe another caliber, though. 300 blackout is kind of intriguing me.

    ReplyDelete
    Replies
    1. I'm familiar with the 80% lowers, and the colfax ones are pretty nice!
      I'm allergic to spending money so I haven't bought anything other than the 0% lowers. The 80% receiver is real nice but I'd rather buy 5 0% lowers than 1 80%. Why?
      Because powermonger politician, that's why!!

      I've got a scraper tool I made for stroking out the corners similar to a broach, but I can't find it for the life of me. For now I just use some files and a small pneumatic belt sander.
      Makes me wish I had a Cnc water jet or an edm machine.

      Delete
    2. Are those 0% lowers still around? I never found those.

      There's a set of AR plans built out of plate. Minor milling, just to form a "rabbet" joint, to use the woodworker's word. It seems to be a very accommodating design. At least, as I recall now.

      Delete
    3. Yup, lots of places have them.
      I bought my last batch of them from a place called Rguns, http://www.rguns.net/other.shtml
      They're listed as paperweights. Not a bad description really, because unless you've got a lot of tools or a lot of time and patience, they're not good for much.

      I have a set of the "laminate" AR plans you speak of. Lots of hole drilling so the works can be bolted together.
      It's pretty easy to get lost in the complexity of building an AR; it seems like it HAS to be a difficult part to make wherein every part, pin, and hole must be exactly in place, within .0001" or it just won't work. The truth is that it really doesn't take much to make a functional AR lower, but it does take a lot to make one that's aesthetically pleasing.

      Delete
  2. James, your projects just rock.
    Thanks for posting this up.
    Also, the first three lines made me laugh out loud (ok, I admit, I heehawed and snorted, but modesty forbids)

    ReplyDelete
    Replies
    1. Thanks KX!

      I hoped people would see the humor in my statement.
      No way I could say that with a straight face, there's no mention of bacon!

      Delete
  3. "Because powermonger politician, that's why!!"
    I heard you saying this in my head as I read it...

    This seriously made me want to try it...

    ReplyDelete
    Replies
    1. ...And well you should!

      That exact line is why I own about half the guns I do. It's the main reason behind the .50 BMG rifle, because someone, somewhere thinks I should not be "ALLOWED" to own/build/shoot one.

      Delete
  4. James-
    I keep bumping into your site as I search various topics and always enjoy your posts. Having been the engineering director at two boeing CNC shops, I can provide some insight on your billet vs forging comment. There IS a difference in strength since the established grain pattern of the metal is parallel in billet and recontoured in a forging. Imagine milling a wood 2x4 and cutting through or interrupting the grain as you plunge through it, vs having the grain formed under extreme pressure around the physical shape of the object. As a force travels through the object it stops and builds where the grain stops and starts. In a forging, there is a smooth path for energy to move through the part. Manufacturers bragging about "billet" anything, know better. Start with a forging whenever you can. It's more costly, but in high stress/ weight sensitive parts, may be the correct way to go. Keep up the good work!
    Rgds, Mike

    ReplyDelete
    Replies
    1. Mike,

      First, welcome, and thank you for your insight. That is good information to keep "in one's pocket", so to speak. I appreciate you enlightening the readers (that come here) of the difference, it may make all the difference in the world to someone who is trying to decide on their first lower!

      You are correct, there is a huge variation in strength between the two, and it can make all the difference in the world in some applications. I guess I should extend my original statement with a bit of a qualifier; that when you are dealing with the very marginal amount of force/s seen on a AR15 lower receiver, it really doesn't make much difference whether it is forged or machined billet. Neither material will be insufficient in *this* particular case.
      In some other case that has to deal with a variety of erratic forces it would likely make all the difference in the world, but here? I'm just not inclined to suggest that someone comparing the two processes would see much difference between the two in functionality overall. Hence my original statement that it "really doesn't matter", because the AR is not going to push material processed either way past it's capabilities.

      Now, if you do want me to give the thumbs down to a method of receiver structuring, we can delve into the dark world of CASTINGS, but I digress. =)

      Thanks for your expert insight on the matter, and please do stop by more often. Feel free to expound on whatever topic you can lend some proprietary knowledge to, that's why this blog is here, sharing information and encouraging others to think and build.

      Delete
  5. guns made of high quality metal are the ones who can fire the strongest and the loudest.

    ReplyDelete
  6. it's ironic that because the lower has the serial number, it got designated as the "weapon". I say ironic because anyone with basic machining skills and a milling machine can make a lower. The hard part to make is the barrel! I think one should stock up on barrels more than on receivers.

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  7. Awesome work, was curious about the jig you made for the magazine well. Did you just design that from the rayvin book? was looking for an easy answer to the magwell problem, but I guess I will have to make one like you did. It seems funny that there are 100 different jig sets out there, but no top plate for the magwell. oh well, another project to build the bigger project. Thanks for the info.

    ReplyDelete