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.  

Finally

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