Cross one off the Bucket List

I had the notion to build an AR for some long while.  I finally go around to it.  This little documantary tells the tale

A couple of years ago I converted an inexpensive manual mill to 3-axis CNC.  I used the mill in manual mode to create all the parts for the CNC conversion.  The electronics were lashed together in a computer enclosure.  I am a retired electronics engineer so that was the easy part.

Having the CNC mill at the ready I decided to start with an 80% lower receiver.  I got the receiver and a jig but decided to use the jig just to hold the receiver in the vise.  Rather than using the jig's top plates as milling guides I programmed the required geometry and toolpaths in CAM software.

Here are some photos of the mill with a couple of test runs in the mounted aluminum stock.  These test runs were actually done after the build during optimization of feeds and speeds.  The receiver was milled with very conservative feed speeds and depths of cut and with a tool change.  The whole operation took about 45 minutes.  I subsequently optimized the CAM software design within the limits of the mill and used a single tool.  Now the whole operation should take less than 15 minutes.  I have a second 80% receiver and will cut it soon.





This is a photo of the CNC controller box which receives commands from a laptop via Ethernet and drives the X, Y and Z stepper motors.



This is a CAM software screen capture of the top view of the cut geometry in purple and the tool paths in cyan.



Another CAM software screen capture in iso view showing the successive depth cuts. 


I wanted to do some engraving so I programmed that into the CAM software and did test cuts in scrap aluminum.  The engraving was filled with a handy product that is a lacquer paint stick -- rub it into the engraving, wait a few minutes and wipe off the excess.




Then it was the matter of working up the spit to cut the 80% receiver.  Enter the victim.


I wish I had take more pictures to include the receiver being milled.  Oh well I'll try to remember to do that for the second receiver and then update this web page.

I decided to powder coat the parts.  Several web instances cautioned against this with the common concern being the powder coat thickness.  I went ahead but did heed the thickness warning. 

I selected a matte desert sand powder coat material.  I did some test coatings and measured the coating thiskness at 3-4 thousands.  When I fitted the milled lower receiver to the upper I ensured a gap between the two to account for the powder coat thickness.  That and tedious masking worked out well.  The finished upper and lower receivers fit together nice and snug.

I also power coated the lower parts kit pieces and the float tube.  Below are a few photos with everything done save for a couple of pieces while waiting for roll pin starter punches to arrive.  Turns out I grew impatient and made some punches on my lathe.  Wouldn't ya know it -- the ordered ones arrived the next day.








I made that little "cleaning link" on the mill.  It is very handy.



And now the fully completed tool.  I mounted a level on the upper receiver.  You can see the little amber colored critter at the rear of the scope mount.


The critter shoots very well.  My wife can consistently make 5 holes in <1/2" at 100 yards.  I do not do as well as I am not as steady as I once was.

THANKS FOR VIEWING MY PROJECT