Any advice on how to dial or hold an ar upper receiver in a lathe and cut the face? Any pictures?
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Gunsmithing Ar receiver truing fixture
- Thread starter flyfisherman246
- Start date
Whenever the receiver truing topic comes up, most seem to think it is a waste of time
(I do mine with one of those Chinese tools)
Someone will always come on and say they true theirs with a lathe.
Others just buy 'Quality'.
So, the OP asked a valid question.
(I do mine with one of those Chinese tools)
Someone will always come on and say they true theirs with a lathe.
Others just buy 'Quality'.
So, the OP asked a valid question.
- Nov 3, 2010
- 9,702
- 20,404
Used my lathe to make the lapping tool. Fit it to my upper for minimal slack on the “guide” part that goes into the upper
I have a lapping tool, I would just feel better about dialing and cutting. Anybody have any ideas for a fixture?
That lapping bar would work as a fixture just drill and tap for a bolt in the ejection port area so it would turn with the bar . Or spin the bar between centers with lathe dog .
Use a 1" rod with a slight interferance fit , make sure it's running true. You don't need a dog or pin, you'll only take a few thou. off the receiver.
I'm guessing you have never checked a receiver to see if it is square across the face.
Here you go. I used the same precision rod on both set up
The bottom picture I use a rotating tail stock chuck and a mini spider. Why so many adjusters? I drilled/tapped the extra set while I had the spider in the super spacer. The rod is held by a copper ring in a set tru 6J to allow the rod to gimble as I adjusted the TS spider.
The top picture I just dialed the rod at the chuck side, TS center just holds the rod
The rod center holes were drilled and single point cut with compound at the correct angle.
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This is what I would do. Mandrel turned between centers, stick it through the receiver. Can't be anything but right.
I can't see holding one end of a mandrel rigidly in a chuck/collet and the other end in a spider unless the TS is seriously out of alignment. Nothing is gained over just sticking it in the center and it's a hell of a lot faster with nothing to dial in.
Yep, the other is a nice fixture but I could square 100 receivers in the time it takes to make it and set it up.
OK..... I get why to do it and it’s pretty cool on the set up and the different way to set it up.
But what about the loose fit the barrel extension has in the upper itself? How the retaining nut tightens down on the shoulder of the barrel extension....are you checking the run out of the barrel extension itself? If the extension has run out in it the nut can possibly put pressure on/cock the barrel into the receiver. Also the diameter of the extension vs the bore of the receiver clearance I think can have an effect as well.
I know guys epoxy the barrel/extension assy into the receiver to take up the loose slack/fit.
Also I’ve seen my share of junk barrel extensions. From run out, to crappy threads, no chamfers on the back side of the lugs, burrs etc...
If your not checking the other things when your doing the assy then recutting the receiver face is helping you how much?
Not poking at anyone so please don’t take it wrong....just throwing thoughts out there for all to think about.
Later, Frank
Bartlein Barrels
But what about the loose fit the barrel extension has in the upper itself? How the retaining nut tightens down on the shoulder of the barrel extension....are you checking the run out of the barrel extension itself? If the extension has run out in it the nut can possibly put pressure on/cock the barrel into the receiver. Also the diameter of the extension vs the bore of the receiver clearance I think can have an effect as well.
I know guys epoxy the barrel/extension assy into the receiver to take up the loose slack/fit.
Also I’ve seen my share of junk barrel extensions. From run out, to crappy threads, no chamfers on the back side of the lugs, burrs etc...
If your not checking the other things when your doing the assy then recutting the receiver face is helping you how much?
Not poking at anyone so please don’t take it wrong....just throwing thoughts out there for all to think about.
Later, Frank
Bartlein Barrels
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Everything on the extension except the lugs, chamfer and feed ramps are cut all in one op. Drilled, boring bar cuts the front of the lugs, threaded, profile, flange cut and parted so all of that should be square with each feature.
Everyone should try to use receivers that are tight to the extension. Vltor Mur and Mega which is now Zev always had a better fit than most I could find.
If the extension has to be tapped into the receiver then the ID of the receiver and OD of the extension hold the extension square with the receiver bore and the receiver really doesn't need to be squared.
Most receivers I squared over the last 12 years are around .002-.003 out of square across 1". If the extension fits loose in the receiver and the face is out of square half of the bolt lugs may be touching and will catch much of the thrust before the bolt lugs on the other side.
We can't catch every single problem but we can try and every thing we catch will help the build.
You guys do everything you can to make sure your blanks are right but it doesn't matter if they are perfect if someone does a shitty job of chambering the barrel or does it with a bad reamer or bad chamber design.
I try to teach people to build better rifles, do everything they can to make it a quality build. If you read on arfcom many say "just slap that shit together, it don't matter" then you read thousands of posts about why they don't cycle or why they shoot 3" groups and it isn't always the barrel quality.
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I special order my competition barrel extensions from BAT Machine with 1.000 OD. On most receivers I have to slightly heat up the front end of the receiver and tap it into the BE. The competition BEs have 20 TPI threads and are 0.3 longer.
Frank,
You are right
I checked runout after chambering, I even check thread runout by running a DTI on the thread with the lathe still set up for threading, verified shoulder for any runout, all checked good, but barrel extension is screwed on and check for runout, the reading is all over. The best ones are the ones I order from BAT Machine. Plus, I like the 20 TPI thread, 1.000 OD, and 0.3 longer tenon.
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Your getting a difference of opinion in this thread on installing barrels.
Everyone is a builder now days buy your mass produced parts slap them together and go blasting . If that rifle can hit a six inch plate at 100 yards great.
Once you get a guy hooked on shooting a rifle that groups well every rifle he buys for now on will have to . Buying good parts from a reputable source will all but eliminate problems unless one slips by . That's where spinning the reciever skimming the front checking for sqaure comes in .
I work hard trying to catch everything so there are no issues afterwards and it's my luck to get the last reciever built Friday before a long weekend.
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