So...after having it sit for a few years in the shipping box, I got it out a month or so ago and determined to get it built. _It_ was an old-school style cast 80% AR lower - the kind with the fully finished mag well and trigger area.
I just had to locate the special tools needed to do the tricky areas..the buffer tube hole ala the big F&*# Drill (BFD) and the big 1 3/16- 16tpi tap. These days those tools are a bit more rare as all the current 80% lowers now have those features completed for you. After months of trying to locate these tools on eBay I was ready to give up and buy them full price somewhere. But with a little help from the Gunco community I was able to get a loaner set of goodies to complete the build. Heck yeah, and a big thanks to everyone involved.
Guidance and reference for the build steps and setup tips came from:
CNCGUNSMITHING - www.cncguns.com - AR15 80% Lower Receiver Tutorial
And the excellent Ray-Vin "Machining the AR-15" free ebook.
Ray-Vin Technical Pages
On to the build...
First up was opening up the buffer tube hole to 1 1/8". I was advised to use a step drill first before the BFD to make it go smoother, and not bind.
No pics of the actual BFD, but prepping with the Uni drill first helped a bunch! The next pic shops my 'unique' bubba style clamping jig. Its some pine molding I had, and was soft enough to not mar the lower. (And cheaper than those fancy drilling jigs)
Next was tapping...using a punch in the chuck it setup nicely, and went thru fast.
After that I tilted the table, and drilled the pistol grip hole (I luv my old Shopsmith). With that done I could then tap that too.
Now the bolt release hole is pretty tricky, luckily the Ray-Vin book shows you how to make a tiny drill jig out of a small piece of bar stock. I made one and then clamped it to lower with a Quik-clamp as shown, then drilled thru with a long aircraft drill.
I did some of the other misc. holes, and then it was time for the holy trinity...Hammer hole/trigger hole/safety selector hole. Doing these just by measurement seemed a bit scary, so I opted to be cheap & resourceful by making my own jig from the PDF DIY template I found that was posted at the WeaponsGuild site. I printed it out and then transferred the pattern to a piece of scrap aluminum I had in the workshop. I drilled the holes and it looked pretty good...
I clamped it up to the receiver left side using the top edge and left casting ridge as my reference points. Drilled the saftey selector hole first , then clamped with a bolt carefully before moving on to the trigger and hammer holes.
After a few more misc steps it was ready for marking. I opted to use electro-etching as I built my own etching machine. I have been having problems using the photo stencils, so I decided to give it a try using the vinyl decal stencil and Q-tip method. (There is a great detailed thread on this at CalGuns by VaderSpade). I was able to get a great custom stencil made up by Tom L. in Az. at a very reasonable $10. He is more than willing to make them for other folks...PM me for his email contact info if you are interested)
Here is the finished etching.
I am setting this up with a AR 7.62x25 custom upper from Prexis, hope to have a final assembled pic up shortly.