The information contained herein is provided for entertainment purposes only.
Check your State and Local laws, in some locations you may need to assign a serial number and register the completed lower, so much for the Ghost part right?!
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The following is my take, my view, my opinion, do not take it as legal advice.
Also laws and restrictions vary by State/County/City, know them for where you live BEFORE you take on an 80% lower project.
ATF notes regarding 80% receivers, you cannot do this for anyone but yourself otherwise, you are a firearms manufacture and must be licensed as such and the lower will become a registered firearm. You can not “barrow” your buddies CNC mill either if he uses it in a business to make money.
Okay now that that is out of the way…
I have done many 80% Aluminum AR-15 Lowers and I learned a few things along the way. Background, all my 80%’ers were done on a drill press, a large Craftsman floor model with adjustable speed via moving the drive belt to different pulley combinations. I have had this drill press for many years. I used the basic jig and purchased the Bit Kit and it was worth it, except for the 3/8″ drill bit, it was junk, I used one I had on hand. The end mills (3 of them) that came with the kit were of excellent quality and are still going.
The basic Jig
Jig drill plate
Drill 3/8″ holes to remove some material prior to milling
Jig Mill Plate 1
Use shortest 3/8″ end mill first
Jig Mill Plate 2
Use 3/8″ long end mill
Jig Thru Mill
Used to guide the long 5/16″ end mill bit to cut trigger opening.
End mills and bits that came in the kit. Worth the 80 bucks.
1st-You do not need to own a milling machine to produce very high quality results.
2n TAKE YOUR TIME you are using an END MILL bit not a side mill an END MILL. It mills from the end of the bit! Duhhh. You will make lots of passes to accomplish an actual Milling machine like finish, many.
3rd You DO NOT need one of those X/Y vises as you see in the photo of the drill press. I used it all of 10 minutes and went right back to free handing it right on the plate of the drill press.
4th You have to get used to the fact that you are not drilling you are milling and as noted above your END MILLING. In guess I would say each pass I would take 1/32″ or less, off at a time. Probably less. Slow and steady and you will end up with a quality job.
5th You set the depth before the pass, usually in one of the holes you drilled out as the first step. Set the cut depth ring and go from there. You never lower or raise the drill arbor during the cutting process. Much like an end milling machine that will stay static and the work piece moves.
6th It makes a huge mess! Aluminum chips everywhere. Have a shop vac at hand and use it often like between every pass.
7th I bought special aluminum cutting oil, save your money use WD40. Remember with any cutting or drilling heat is a killer of tools.
8th Take Your Time, take off very small amounts off with each pass 1/32 better yet 1/64th, even if you have to make 100+ passes.
9th When drilling through for the trigger hole…SET DEPTH gauge ring, if you have a lower that has a trigger guard built in the last thing you want to do is cut into it! Drill a 5/16″ pilot hole FIRST to put the end mill bit through and 1) check depth/set gauge 2) prevent from creating a wide spot in the opening you are about to cut. Plunging the 5/16″ end mill through the bottom to create the trigger hole causes the mill bit to walk and you will end up with a noticeable wide spot, it wont affect the operation of the lower but its avoidable by doing the pilot hole first.
10th Take your time, if you have not noticed, I have repeated this often. It may take you 4 hours of milling but in the end you will have a piece that looks like it just came off an actual end mill or CNC and with no serial number ;). (see disclaim above regarding State and Local Laws) .
11th Direction matters. I would mill from the left side towards me (pushing work piece away from me), then the right side pulling the work piece back towards we. This has to do with the direction of rotation of the drill press. Speed matters as well, you do not want to force it and cause the work piece to chatter. A few minutes of doing the milling and you will hear and feel what the right speed is.
12th There is no cost savings by doing an 80% lower it actually cost more than buying a machined finished register-able receiver. But a serial number is not required in most locations, (see disclaimer above regarding State and Local Laws). My guess is you can thank the manufactures for the higher cost “because they can”.
The end result