Ar15 Lower: Jumping In

n3480h

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Finally got one of my 0% forged lower castings on the mini-mill. Fixture plates were first machined with Ray Brandes' tutorial, and they have worked well. The mill is a HF to which I have added iGaging 3 axis DRO units. Being a cheapskate, I resisted buying a 1" center cutting mill for the 3/4" radius at the rear of the casting, choosing instead to set up a small flycutter (LMS 3 piece kit) and making test cuts until the correct radius was achieved. Tedious work, but I am amazed at the very good finish this tool made as it was eased through plunge cuts until the final coordinate was reached. Driver side holes were spotted and drilled yesterday. Being a rank amateur, I would hate to attempt this project without the Brandes guidance and the little iGaging DRO. As it is, this is great fun and very educational.Lower milling2.jpg Milling lower.jpg Tom
 
Please keep posting as you progress. I'm very interested in this project.
 
When you do these I found that I used one spot for the zero point and all measurements go from there. If you keep your DRO numbers recorded for future work you will find it gets easier. I put all measurements on 4x6 cards. If you get a copy of lower receiver blueprint off the internet and have it blown up to about 16x20 size you will find it will go much easier. Take you time and really think it out on every move when you get to cutting out the mag housing and trigger group pocket. Good luck you will find that you will learn quite a bit.
 
Looks like fun, I'd love to do one but unfortunately, I live in a state where I'd be facing the rest of my days in the slammer for such activities...
 
When you do these I found that I used one spot for the zero point and all measurements go from there. If you keep your DRO numbers recorded for future work you will find it gets easier. I put all measurements on 4x6 cards. If you get a copy of lower receiver blueprint off the internet and have it blown up to about 16x20 size you will find it will go much easier. Take you time and really think it out on every move when you get to cutting out the mag housing and trigger group pocket. Good luck you will find that you will learn quite a bit.

Thanks Buddy. I am learning a lot, especially about how to counteract the mini-mill's generous worm screw "tolerance", lol. Even with all that, I can still be reasonably accurate - but it does make me want a good Bridgeport. Brandes instructs to use a wiggler to set a preliminary zero off the center of the mag release button . . . . and then move X-Y to establish the zero for the takedown pin location. That then becomes the reference zero for the machine ops on the driver's side, and the top plane and rear radius (and the back plane of the buffer). The main problem here is that I am a recovering QC inspector for a medical device manufacturer: This made me one picky S.O.B., so now none of my work in my little shop is ever as good as I want it to be. But if the lower functions properly in the 300 Blackout build I will be satisfied.

I'll be posting more on the machining experience soon. Dog refuses to vacuum or do dishes, so I need to finish those chores before I can get back out in the shop later today. BTW guys, I appreciate the interest in this thread. Kind of a bold undertaking for me, but I bought two of these castings in case I screw this one up. Yep, CYA.

Tom
 
Finished milling the driver's side today. Very pleased that the pins, mag release, and the safety fit very well. Flipping the forging over to run the passenger side tomorrow.
Tom
AR Pass. Side milled.jpg
 
I know what you are saying, never enough time in the shop. Those of us who have done these bought at least two forgings but if you take your time you will get it in one shot. If you are going to put serial number on it, be sure to stamp before doing interior cuts. Not sure what your local rules might be. You will like the 300 Blackout, great round.
 
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