Saturday, October 30, 2010

New Project Underway

I've been a little quiet lately because I've been a little busier lately.  I have a new project underway, making an AR-15 from an 80% lower and a pile of parts.  Thanks to the fine folks at Colfax Tactical, I have a lower receiver forging on the CNC mill and I'm in the process of finishing the last 20% that makes the lower receiver functional. 

Why this project?  First off, as someone observed before, "ARs are like potato chips: you can't stop at one".  My main use for my AR has been remote paper punching, and I'd like to have another with a longer barrel (mine is 16").  A second reason is the answer to "why climb that mountain?".  I enjoy doing things in the shop, I have a CNC milling machine, a drill press and everything I need to take on this project, so why not?  Finally, under BATFE rules, the lower receiver is what constitutes a gun, and an 80% lower is not useful enough to be considered a firearm.  It's a paperweight which can be bought without an FFL transfer.  So for a few hours of work in the shop, you can turn a paperweight and a handful of springs and things into something very useful. Once you turn it into a gun, you don't legally need to put a serial number on it; it's probably easier to put a number on it than to explain to the nice officer why your gun doesn't have a serial number!
I elected to buy the optional fixture that Colfax sells, because this is my first one.  Perhaps if there are more in the future, I'll work with the raw castings/forgings.  The first step is to center the drilling guide over the area that will be hollowed out - this is the fire control pocket, where the trigger and safety are located.  This photo shows me marking the hole locations on my drill press.  Once that was done, I moved it to the milling machine.

Once it was on the milling machine, I immediately discovered that the work holding clamps for the mill wouldn't securely grab the fixture, so I had to go back over to the drill press and modify the fixture.  This clamp is holding onto a 1/4-20 machine screw that wasn't there. I had to drill and tap the holes for it to make the fixture usable to me.  There's one on each end. 

The first holes to drill out will become the trigger slot.  These need to have 1/8" guide holes through drilled, followed by a 5/16" drill, all the way through the forging.  All of the rest of  the marks will get 1/8" and then some get 3/8" holes drilled to "hog out" most of the metal.  A drill is pretty much the fastest way to remove metal, especially for a small, low horse power mill like this.  
Both of these pictures were taken while drilling (specifically, running a CNC G83 "Peck Drill" cycle), but the flash froze the motion.

That's the latest here at Castle Graybeard.  I'll update it as I move along.  For those interested in more info, besides commenting here or email to my blog account, you can find information at the CNC Guns forums, and main web site.  As far as I know, I'm the first person to do this on a Sherline mill.  Well, hybrid Sherline and A2Z CNC mill.

Edit:  10/30 2235   That dastardly typo gremlin edited my post after I put it up.  I swear that little guy gets me all the time. :-D  


  1. Stamp it with a "1."

  2. I'm going to CNC engrave it.

    Mrs. Graybeard says we should name it after our cat, Mojo (Moe). Make up the fictitious name "Moe Guns", as in "who doesn't want Moe Guns?".

  3. Moe's Bigguns? :-) Nice! Makes me wonder if I should buy a little Unimat and set up the Mill part to try doing what you're doing too - but I'm afraid it may not be really up to that task, and I'm not particularly familiar or good at metal work, and besides I have a buddy with a huge X-Y-Z machine who can do mchinistry things blindfolded.
    But it would be cool to have one (a Unimat).

  4. DirtCrashr: you don't really need a mill. A drill press is really all you need, with a few common drill bits (1/8, 5/32 and 3/8 if I recall). I think a bench-top ("8 inch") drill press would work. An X-Y table on the drill press would help, but is not essential. A hand cranked mill would be excellent, and while I've never touched a Unimat, my guess is it would work.

    CNC Guns Drill Press Tutorial

    What I'm finding is that doing it in my CNC system is slowing me down, so I may end up finishing it on the drill press.

    Right now, my lower looks more or less like this.

  5. Looks nice! I just need an excuse to get a Unimat, and then the expertise to go with it. :-) My friends massive XYZ machine could whip it out in seconds, it cuts steel like butter. He kinda does skunk-work for Google.

  6. If it makes you feel any better, when I got my Sherline a few years ago, I don't think I had ever even touched a milling machine. Maybe I bumped into one in a shop by accident, but I sure never used one.

    I've learned everything I know reading and making some chips of metal, wood and wax.

    Over on the CNC Guns site, the guy shows how he made a complete lower from a solid block of aluminum, like your friends' machine. I'd love to have that capability, but I can hardly walk in my garage as it is.