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Posted: 11/28/2004 4:08:32 PM EDT
I have found at least four AR lower drilling jigs. They are OSI, The Tannery Shop and CNC Gunsmithing and one from hicapmags. Each has its stong and weak points. Anybody know of others out there I can look at?
Link Posted: 11/28/2004 9:22:21 PM EDT
I can't really think of any other jigs out there at the moment...

Personally, I'd reccomend that you buy the CNC model directly from Justin (the creator) at www.cncgunsmithing.com/tooling.html
It is only $99 shipped. He's one of the good guys.

I think the CNC model is the most economical and efficient design out there right now. Just keep in mind that the 80% receiver you use with it MUST have the top plane already machined to proper dimensions. Almost all the forgings out there do anyway, so it's not a concern unless you're doing one of them castings, that still need the top plane machined.

The only thing the CNC ain't got that some of the others do, is the backplate used to help in reaming and tapping the buffer tube hole. No biggie. I just stood my CNC jig and receiver up vertically in my drill press vice, and used a 1" drill bit chucked in my press and pressed into the buffer hole, to center the jig, then swapped that out with the 1 1/8" reamer bit to ream the hole out. This is a scary process. That 1 1/8" bit, trying to ream out the 1" hole is going to chatter like MAD, and start to bind up once you near the bottom of the buffer tower. Go VERY slow. Pray often. Check for straightness even more often. Things seem to straighten up and calm down once you get about a third of the way down.
Use the same set-up for tapping that hole. Chuck a center punch, or a philips head bit in that press, and lower it down onto the dimple in the back of the tap. Have a buddy apply pressure to the press, while you use a wrench to turn the tap by hand. 1 full turn- then back it up a quarter turn. Repeat until tapped all the way through. Tapping is a piece of cake with this method. The monster tap chewed through the aluminum like it was butter.

I finished my first 80% with nothing more than the correct bits, a 12" drill press, a vice, a dremel with sanding drums, and the CNC jig. Turned out perfectly, and has zero upper to lower slop. Don't even think of trying this without a drill press though. You need one that has at least a 12" clearnace from spindle to table, for the reaming/tapping procedure.

If you still need all the drill bits and taps, I reccomend you order from Enco.Enco Check out my invoice below. That's ALL the bits and taps you need, with the order numbers, plus a few extras in case you break or dull one, for under $60. I seen the monster tap ALONE go for $60 elsewhere. You probably can't beat this price, considering these are mostly top tier quality, made in the USA cobalt bits.

300-2308 1/8 COBALT JOBBERS DRILLS 1 $1.01 $1.01 (trigger guard)
300-2310 5/32 COBALT JOBBERS DRILLS 2 $1.04 $2.08 (fire control holes)
300-2314 7/32 COBALT JOBBERS DRILLS 1 $1.61 $1.61 (pistol grip hole)
300-2316 1/4 (E) COBALT JOBBERS DRILLS 1 $1.81 $1.81 (take down holes, buffer stop)
300-2324 3/8 COBALT JOBBERS DRILLS 1 $4.49 $4.49 (selector)
301-1072 1 1/8 HS SILVER & DEMING DRILLS 1 $12.29 $12.29 (buffer tube hole)
311-6013 TAPER RT HAND,4FLUTE 1/4-28 CARBN STEL HND TAP 1 $.95 $.95 (grip tap)
313-0531 1 3/16 X 16 PLUG H.S.SPEC.GROUND THR.TAP 1 $29.35 $29.35 (buffer tube tap)
240-6520 3/32 118 DEG BLACK TRIUMPH HSS JOBBER DRILL 2 $.67 $1.34 (misc. detents)
891-6750 3/32 COBALT USA 6IN AIRCRAFT EXT.DR. 2 $2.08 $4.16 (bolt release)
Sub Total $59.09
Shipping $.00
Tax $.00
P/S Total $59.76
You have Applied the following promotions:
CZNRFS - Free UPS Shipping

*PS, you'll also need a 3/8" and a 1/2" endmill for the flat bottomed stock index hole, and to clean up the rear take down hole face. I already had a cheapo Harbor Freight endmill set, so I didn't bother ordering more.
Link Posted: 11/28/2004 9:52:08 PM EDT
corpseknight, where did you get your 80% lower at?

Link Posted: 11/28/2004 10:40:16 PM EDT
[Last Edit: 11/28/2004 10:51:12 PM EDT by corpseknight]
I bought the HPS from National Ordnance.https://www.vbd.com/noc/shop/products_detail.asp?CategoryID=29&ProductID=122
It had a very nice looking silvery finish when I got it. I asked them what the heck it was and they responded with; "The receiver is high temp degreased. The receiver is then frozen vapor blasted with frozen Zircon to create a very tight skin surface with a satin finish." Sounds good to me, even though I have no idea what that means. All I know is this thing looks sweet, fit my upper perfectly, and is straight as can be.

It had the trigger guard and front pivot holes pre-drilled. The inside of the FCG well, and rear takedown lug well, needed to be widened out a bit. That was a pain in the ass since all I had was a dremel to do it with. You need to lose about 1/16 off either side. The plus side is that you can custom fit the lower to the upper. The gun feels very solid when assembled.

I've heard some bad things about National Ordnance in the past, but they've done me right so far. Shipped my receiver out in 2 days, and had like $4 fixed shipping.

My buddy, who shared the jig and drills with me had one of the receivers Scott used to sell through the CNC website. Took him half the time I did, since all that one required was hole drilling and tapping. No messing around with the dremel. Unfortuantely, Scott seems to be out of stock! have
All in all, I must say this was a very rewarding project. One of the plusses about building an 80% is the fact you can do a little customizing while the receiver is still in the white. I gave mine a "meltdown" around the grip area. The trigger guard gap got rounded off and I smoothed out all the forge marks. I'm in the process of applying a custom logo and lettering(the SAFE and FIRE text is missing on both these receivers) right now. I just need to figure out the best way of going about this. I am looking into electrochemical etching, since it'd be cheap and accurate. But I'm not sure how well it'd work on aluminum, and if I could get it to etch deep enough. to be very visible. If that doesn't work out, I have a $10 set of stamps from Harbor Freight on the way. hing
Link Posted: 11/29/2004 9:53:23 AM EDT
Thanks corpsknight. I have several of the forgings from Scott that I will be working on. Quality items for sure. Sent him a couple of emails asking questions. Prompt and friendly replies. The CNC is a qual;ity product and I may go with them. Thanks again.
Link Posted: 12/6/2004 10:31:33 AM EDT
I just picked up a jig and bit set from byogun.com. The bit set includes an end mill to clean up the fire control recess, as well as a tap for the pistol grip hole. The jig looks pretty good, and comes with the back plate to guide the buffer tube, stock plate index, and takedown detent holes. The thing is that the buffer tube guide is tapped. This seems good from the standpoint of getting the tap lined up just right, but I'm wondering how long the threads will last if I use the 1-1/8" bit to drill the buffer tube hole with the plate in place. I'm really thinking I'll end up finding a reamer to open the hole up, then just use the plate to get the tap started.

On that subject, most of the 1-1/8" spiral shell reamers I've seen run around $50-60. However, there's one here listed for $26:


Any reason why that one wouldn't do the trick? I'll still need the bushings to line it up with an upper receiver, but that just seems like a much more solid and reliable way to get that hole bored.

Link Posted: 1/10/2005 5:48:11 PM EDT
Thanks for all the help guys. I have the CNC jig now. The buffer tube hole was a big problem. The reamers that I have found, do not have a taper to them and are almost impossible to start. There is a thread here on making a piloted reamer. I used it as an example. I also got some adjustable reamers and reamed the hole in steps to make sure it was square. Its probably the shadetree way of doing it but it sure worked nice. I've started making my own drilling jig. I'm never satisfied. I'll let you know how it turns out.
Link Posted: 1/11/2005 4:46:58 PM EDT
I was lucky enough to get 2 of Scott's lowers before they were out of stock. Very nice work. I am still trying to work up the nerve to drill the 1 1/8 hole. It sure does create a hell of a raket while drilling. I am always afraid that the lower is going to break and back off. I will have to try it again after having a few 'cold ones' to calm my shattered nerves. Justin's jig worked like a charm and I had all the holes drilled in the 2 lowers except for the buffer done in a matter of a couple hours. I would reccomend Justin's jig to everyone getting into building your own.
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