Author Topic: Pilot Reaming the Buffer Tower  (Read 13139 times)

Offline goober

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Pilot Reaming the Buffer Tower
« on: December 06, 2008, 06:59:18 PM »
First off, stop snickering at the title. All done? OK.
It seems there are a lot of first-time 80% AR15 Builders around here lately, and lots of questions about various steps in the 80% lower finishing process. Many peeps are now using the new lowers from Kevin, so the discussion has concentrated on ways to finish the FCG pocket that is now solid on these 80's. The Ray-Vin tutorial is a great reference for this (and other) operations, and Justin has a new jig adapter to help with this.
Kevin's new lowers have the buffer tower already drilled and tapped, which most folks find a welcome improvement. This change eliminates the need for one of the trickier sets of operations that always seems to give folks trouble (and generate questions): drilling/reaming/boring out the nominally 1" existing hole in the buffer tower, and tapping it to 1 3/16"x16. Its pretty crucial that these steps be done correctly if the paperweight is going to graduate into a fully functional semi-automatic rifle receiver.

So, for those of you that are starting with one of Kevin's new-style 80% lowers, this tutorial is not relevant to your project, as it covers operations you do not need to do (they are done already). But for anyone starting with an 80, 10, 0, or other lower that has the buffer tower hole unfinished, and for those that are just interested, please read on...

There have been a few threads here around the topic, both folks sharing ideas (like ferretface's post) and others asking questions. Well here's another.
First of all, I can't stress enough how useful it is to read every tutorial you can find. This includes Justin's, The Builder's Squad Project, Building the KT-15, and whatever else you can find. Although they are more directed towards finishing a raw (0%) casting/forging, the Ray-Vin and 5Bears tutorials also have a wealth of useful information for the 80% builder. So read them all, multiple times, and you will better understand the project and increase your chance of success.

That being said, I will extract and present for you what I feel is the best, most foolproof way to open up the buffer tube hole: the piloted reamer method. I realize this may become pretty much a non-issue if more 80% lowers begin showing up that are like Kevin's new ones (or KTO's old ones) where the job is already done. But I'm sure there will be unfinished lowers out there for some time to come that need this operation done, so here goes...

Problem: the existing buffer tower hole needs to be opened up to 1 1/8" before tapping. Many tutorials will call for a monster 1 1/8" Silver & Deming drill bit for this task, and this is what most vendors will offer in their "finishing kits" or tool sets. It's big and heavy and impressive, and you can use it to accomplish the task. But there's a better way.

Complication: On some 80% lowers, the existing hole may be off-center, or the outside dimensions of the tower itself may be a bit misaligned. This can make it very difficult to locate the giganto-bit correctly; what you want is a hole that will be perfectly aligned with the inside of your upper, where the bolt carrier is going to be zipping back and forth on every shot. If you just center the big bit in the existing hole, and it is not located properly, you may not end up with your drilled hole aligned correctly. On top of this, the bit is huge, and the flutes are large and deep, so it is prone to chattering and biting, even if you do run your drill press as slow as possible (assuming the jigged lower and bit will fit in your press). Also you need to really clamp the bejeezus out of the lower to hold it rigidly enough during the drilling. It needs to be really solid.

Sooo, why not just ignore the placement of the original hole, avoid relying on the potentially dubious oustide dimensions of the buffer tower, and ensure the hole will be aligned correctly by using the mating part? This is the basis for the piloted reamer method, which uses the upper (and thus the location of the BCG) to locate the buffer tube hole.
« Last Edit: December 28, 2008, 03:17:25 PM by FUBob »
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Offline goober

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Re: Pilot Reaming the Buffer Tower
« Reply #1 on: December 06, 2008, 07:07:52 PM »
Note that I've stolen not only this idea but pretty much all these images from the Builder's Squad Project or elsewhere. I take no credit for any of this.

Step 1: Don't buy (or don't use, if you already bought it) the giant 1 1/8" drill bit. Save your money and buy the parts you need to assemble the pilot reamer tool (or buy one
ready-made).

Step 2: Complete all operations on your 80% needed in order to fit an upper to it (top deck in spec, pivot and takedown pins holes drilled, FCG pocket and pivot pin "ears"opened up
if needed).

Step 3: Have your upper on hand.

Step 4: Buy or assemble a pilot reamer setup. This includes the following pieces:

a) a 1" diameter x ~4" long bushing (brass, plastic, or other non-marring material) with a perfectly centered hole that fits your chosen arbor (or, *ahem* shaft) tightly. This will
fit snugly inside your upper receiver (with the BCG removed).
b) some means of making the reamer fit the arbor tighlty and well-centered. This could be anything from a few turns of electrical tape, to some vinyl tubing, to a steel bushing. Whatever works.
c) a 1 1/8" spiral shell reamer that will fit on your arbor.
d) a ~10" long arbor or shaft that fits insdie your bushing and will also accept a spiral shell reamer. A 10" long 3/8" socket extension works great for this.
e) a 3/16 x 1 3/4" roll pin.

Step 5: Drill a 3/16" hole straight through the arbor about 1 1/2-2" from one end (the fat female-socket end *ahem* if it is a socket extension).

Step 6: Drive the roll pin through the drilled hole so that an even amount protrudes from each side.

Step 7: Wrap 5-6 turns of tape or place whatever material you are using onto the arbor near the roll pin (on the male-end side of the pin) in order to snug the fit of the reamer.

Step 8: Slide the reamer onto the arbor, over the snugging material, and up against the roll pin so that the pin sits in the notches on the back of the reamer.

Time to get set up to ream. Schematically, this is what we are after (but with the upper on the lower):


Step 9: Clamp your lower in a vise. Place the bushing in your upper and your upper on your lower. Pin the upper in place.

Step 10: Run the arbor (with the reamer on it) in through the original buffer hole, into the hole in the bushing that is inside the upper. Bring the spiral reamer up against the rear
plane of the buffer tower.

Step 11: Using manual power or an electric drill, spin the reamer and begin boring the hole. BUT:

Step 12: DO NOT REAM TO DEEPLY!!! Stop well before the front cutting end of the reamer gets too close to the front (inside) edge of the buffer tower! If you go too far you will trash
your upper!

So, after you get started, stop reaming (I know its hard but bear with me), unpin your upper and slide it forward a bit, so that there is a gap between the front of the buffer tower
and rear of the upper. Clamp the upper in place. Now resume reaming until the hole goes all the way through.


That's it. You now have a perfectly aligned 1 1/8" hole that is ready to be tapped.


If you're interested in obtaining a pilot reamer setup of your own, go here...  ;D
« Last Edit: December 09, 2008, 01:28:19 PM by goober »
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Offline 3sixbits

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Re: Pilot Reaming the Buffer Tower
« Reply #2 on: December 08, 2008, 11:24:25 AM »
So then if a guy misses the one and only for sell on this site, where did you find this tooling?

Offline goober

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Re: Pilot Reaming the Buffer Tower
« Reply #3 on: December 08, 2008, 12:20:49 PM »
So then if a guy misses the one and only for sell on this site, where did you find this tooling?
I'll be posting a FS ad on Homegunsmith as well as Arfcom at some point. I'm giving you guys the first crack at it.  ;D
There is not just one of these setups; I make them to order. With the exception of the 1" brass bushing, all the parts are easily obtainable.
The bushing itself does not have to be brass (that's just what I use), it just needs to fit the upper snugly, be non-marring, and have a centered hole that fits the arbor.

The How-To above describes the process of making a pilot reamer setup yourself.
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Offline mfachar

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Re: Pilot Reaming the Buffer Tower
« Reply #4 on: February 03, 2009, 01:07:33 PM »
That's good stuff man keep it up Thanks!
I choose not to be a victim....

Offline Mil-Surp

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Re: Pilot Reaming the Buffer Tower
« Reply #5 on: February 03, 2009, 01:32:16 PM »
Uber cool!  I like the way you think!

Offline goober

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Re: Pilot Reaming the Buffer Tower
« Reply #6 on: February 03, 2009, 08:30:08 PM »
Thanks guys!
Again, I can't take credit for coming up with this idea, only for perpetuating & spreading it...
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Offline highxxx

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Re: Pilot Reaming the Buffer Tower
« Reply #7 on: April 01, 2009, 03:39:32 PM »
happy\
to
you
n youn

Offline Ryo

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Re: Pilot Reaming the Buffer Tower
« Reply #8 on: April 06, 2009, 03:57:01 PM »
Very nice. 

Offline VaderSpade

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Re: Pilot Reaming the Buffer Tower
« Reply #9 on: April 12, 2009, 08:50:07 AM »
 I finished my first 80% using an AR-15Plus HPS Forged Receiver (Iím saving my yellow logicís till I work out the kinks).

 Pilot Reaming the Buffer Tower with gooberís tool worked like a dream.

 I am now waiting on an anodizing kit I ordered from http://www.focuser.com/atm/anodize/anodize.html

Offline goober

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Re: Pilot Reaming the Buffer Tower
« Reply #10 on: April 12, 2009, 09:39:37 AM »
I finished my first 80% using an AR-15Plus HPS Forged Receiver (Iím saving my yellow logicís till I work out the kinks).

 Pilot Reaming the Buffer Tower with gooberís tool worked like a dream.

 I am now waiting on an anodizing kit I ordered from http://www.focuser.com/atm/anodize/anodize.html

Great to hear, VaderSpade!
Regarding the ano kit, my biggest suggestion is to invest in a decent constant-current/constant voltage power supply, such as one of these from Mastech... only about $250, less if you get the lower amp-rated one. you can make do w/  battery charger (non-automatic type ONLY) but a good PS will give you more control and much better results.
i use the same kit from focuser as far as chemicals and such go.
the anodizing DVD from Roderus is also good, and there are lots of good threads on the forum there.
as i'm sure you've read, following the directions and being careful about having the parts clean, handling only w/ gloves, and rinsing well to avoid cross-contaminating your baths are all important. keep the part wet w/ DI H20 b/w baths if it needs to sit out for any time.
and finally, the electrical connection to your part must be nice and robust and waterproof to avoid the connection itself anodizing, thus breaking your electrical continuity.
but be safe & have fun!
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Offline VaderSpade

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Re: Pilot Reaming the Buffer Tower
« Reply #11 on: April 12, 2009, 10:45:18 AM »
Thanks, for your advice.
 I am going to my storage unit today to pull out some gold plating tools I have. I have done a lot of gold plating and stripping (although itís been awhile). Anodizing seems to be along these same lines. Iím hoping my plating power supply (I bought a good one) will work with my Anodizing. I will check specs with the power supply in your link.
 At some point I plan on solid gold plating that Golden gun receiver I bought. I have the supplies, and gold plating solution just sitting in storage, so what the heck.

Then I may change my name to the man with the golden gun!

Offline goober

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Re: Pilot Reaming the Buffer Tower
« Reply #12 on: April 12, 2009, 12:47:38 PM »
well if you're an old hand @ plating, i'm sure you'll be successful w/ ano  :)
can't wait to see the golden gun, as well!
« Last Edit: June 03, 2009, 09:02:22 AM by goober »
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