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Old May 17, 2017, 22:37   #1
Dean762
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Imbel barrels and threading issues in a DSA reciever ?

I recently purchased 2 parts kits with Imbel parts and barrels. One barrel had the receiver stub and the other had had it removed before I received it. I also purchased a DSA R1 forged receiver. I took the kits and the receiver to 308/223shooter who happens to live in my general area and has had considerable experience in building Fals to assist me in building a gun, after he graciously offered to help.

Once we got everything organized and attempted to barrel the receiver with one barrel we discovered that the threads were so tight that it was impossible to even get close to checking the timing. I thought maybe it was the receiver so we tried the other barrel and had the same issue. 308/223shooter had some other barrels and tried one (or two?). His barrel was also an Imbel and it threaded onto the receiver and timed almost perfectly with no problem. My first thought was that maybe the threads needed to be chased. I had purchased both tap and die from Brownells in 1 /16 thread pitch so I chased the threads in both the receiver and one of the barrels. I once again attempted to thread the barrel into the receiver but the same problem. I also tried some anti seize but that did not work.

Has anybody else had this issue ? Any thoughts or assistance would be appreciated.

So far I have a very expensive pile of parts and no gun.

Thanks

Dean
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Old May 17, 2017, 22:42   #2
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1 ) Insufficient relief at the lead of the thread, and at the juncture of the thread / torque shoulder can prevent the barrel from seating.

2 )Did you chase the Parkerizing from the receiver threads ?


3 ) Anti-seize is an unnecessary step.


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Old May 17, 2017, 22:46   #3
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Yes I did.

You are right about the anti seize. Just a Hail Mary.

Thanks
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Old May 17, 2017, 22:48   #4
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Yeah, spotted the wonky barrel threads strait away. They looked almost rolled, and looked flat instead of sharp. I tried three of the barrels I had on the bench, { waiting on cash for receivers I just can't stop. } and they all hand timed without issue. For once, I can't blame DSA QC for this one.
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Old May 17, 2017, 23:21   #5
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I've had several Imbels that thread on super tight. So tight that I could not tighten them "by hand" and I had to use a wrench to "hand tighten" them to check timing. They usually get tight about 3/4 of the way into the receiver. I've built all of my Imbels on Imbel receivers so I can't speak to the fit with Imbels and DSA.

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Old May 17, 2017, 23:43   #6
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I've had several Imbels that thread on super tight. So tight that I could not tighten them "by hand" and I had to use a wrench to "hand tighten" them to check timing. They usually get tight about 3/4 of the way into the receiver. I've built all of my Imbels on Imbel receivers so I can't speak to the fit with Imbels and DSA.

.
Both of the barrels get about 1/4 to1/2 the way on and they become so tight that it is really doesn't seem advisable to even attempt to continue.

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Old May 18, 2017, 07:03   #7
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Both of the barrels get about 1/4 to1/2 the way on and they become so tight that it is really doesn't seem advisable to even attempt to continue.

308/223shooter
Oooh, yea that sounds too tight.
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Old May 18, 2017, 08:18   #8
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"AOL will not accept delivery of this message." Don't think I was ignoring you!

This happens every once and a while to people who still use primitive AOL. Not sure why, but AOL frequently blacklists gun domains as spam. So my reply to you was rejected.

I don't know what to tell you - if you've chased the threads on both, then what else is there to do?

I did a DSA R1 yesterday and ran into the same problem with the receiver threads being tight, but I ran a tap on the receiver and the IMBEL barrel screwed on just fine by hand.

Only on rare occasions to I find a combination of parts where the barrel needs a wrench for light effort prior to final timing. If you're needing a wrench and cannot turn by hand when still several threads out, there is something wrong with the threads on one, the other or both.

I assume your 1"x16 die is an adjustable one. Try tightening it slightly and chasing the threads on the barrel again. And if your tap is not a bottoming one, but a taper, then you aren't getting the first three or four threads from the inside.

Doesn't matter what it is, if both bolt and nut are 1"x16 (and a 2A/B), then if they fail to screw smoothly together, one or the other is NOT 1"x16 2A/B

Both barrels were on IMBEL receivers already. While it is common to clean up and "sharpen" the threads, I would assume the DSA receiver to be the culprit.

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Old May 18, 2017, 10:04   #9
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I've ran into this problem before and that why I own taps and dies. You just need to clean up, or re-cut, the threads. This is a SIMPLE fix!

Not to sound snarky but there is a reason gunsmithing is called gunsmithing, because every once in a while you have to have the knowledge and tools to fix the parts of a firearm.

I'm not currently an FFL and don't have my "Gunsmith" shingle hanging out right now, so the best bet is to send them to Mark to fix.

One thing you should also realize, some of the time the tools you use need to be modified. I had to grind my tap down to get a full depth of threads in the receiver. I may have taken my die and ground it down as well, to completely clean up the threads on the barrel. Most people don't have precision grinders to modify tools like this.
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Old May 18, 2017, 10:06   #10
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I've ran into this problem before and that why I own taps and dies. You just need to clean up, or re-cut, the threads. This is a SIMPLE fix!

Not to sound snarky but there is a reason gunsmithing is called gunsmithing, because every once in a while you have to have the knowledge and tools to fix the parts of a firearm.

I'm not currently an FFL and don't have my "Gunsmith" shingle hanging out right now, so the best bet is to send them to Mark to fix.

One thing you should also realize, some of the time the tools you use need to be modified. I had to grind my tap down to get a full depth of threads in the receiver. I may have taken my die and ground it down as well, to completely clean up the threads on the barrel. Most people don't have precision grinders to modify tools like this.
What do you do with the barrel when re-threading does not correct the problem? The threads appeared to be flattened from the shoulder to the chamber. First time I've seen a barrel this bad, and I've seen quite a few.
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Old May 18, 2017, 10:18   #11
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I assume your 1"x16 die is an adjustable one. Try tightening it slightly and chasing the threads on the barrel again. And if your tap is not a bottoming one, but a taper, then you aren't getting the first three or four threads from the inside.

Adjusting the die until the barrel screws in will allow the receiver and barrel to mate, but really isn't the correct way to fix this. Tapping the receiver is, as you mentioned above.
I would definitely run the die over the barrel, to make sure it's to spec, and clean.

As for the taps, sometimes you need two, or three, taps with different grinds to repair a part. Running one tap in first, then the second tap (and/or third tap), until you have the blind hole completely tapped. There are NO over-the-counter taps that will thread to the bottom of the receiver, not even a bottoming tap. You still need to grind off a few teeth of the tap to hit bottom.

I'm sure these receivers have their threads cut on CNC machines with thread cutting tools, not taps, and it simply boils down to either their machinists don't know what they are doing, or don't care. A little QA would have caught this before they ever left the plant. A simple GO/NO-GO gauge sitting at the machine to check parts coming off would be very helpful! And if they have them and don't use them, then it's simply a case of "I don't give a f*ck!"
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Old May 18, 2017, 10:22   #12
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What do you do with the barrel when re-threading does not correct the problem? The threads appeared to be flattened from the shoulder to the chamber. First time I've seen a barrel this bad, and I've seen quite a few.
Without having the barrel in hand, I can't tell you if it's a damaged barrel or simply a barrel that was cut that way. If the O.D. of the barrel is on the smaller side, you'll see flat threads. But that doesn't mean the threads are out of spec. Threads don't engage at the top of the peaks, or at the bottom of the valleys. They contact each other on the side of the thread.

As Mark mentioned, the barrel was used before so that would mean your receiver is not correct. I'm sure it will need to be tapped. I've done a few DSA receivers that needed it.
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Old May 18, 2017, 10:26   #13
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But, even if the receiver needs to be tapped, I would still run a die over the barrel. The threads have stretched and need to be cleaned up. I don't tighten my die down and cut the threads smaller (unless absolutely necessary!!!).
I use the die to simply clean, and take a little metal off where the threads stretched.
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Old May 18, 2017, 10:52   #14
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Originally Posted by Dean762 View Post
I recently purchased 2 parts kits with Imbel parts and barrels. One barrel had the receiver stub and the other had had it removed before I received it. . . .we discovered that the threads were so tight that it was impossible to even get close to checking the timing. I thought maybe it was the receiver so we tried the other barrel and had the same issue.
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What do you do with the barrel when re-threading does not correct the problem? The threads appeared to be flattened from the shoulder to the chamber. First time I've seen a barrel this bad, and I've seen quite a few.
Again, "does not compute".

Even if there was "something wrong" - threads stretched, stacking of tolerances, etc. - once you've chased both to the same, they are the same. That you claim to have used a 1"x16 die and a 1"x16" tap, they both must now be 1"x16".

Are you using a receiver wrench?
Is it just as tight whether using the receiver wrench or not?
I have had some receiver wrenches, when over-tightened, press inward on the threads enough to cause undue tension on the barrel. This has only been to date with coonan receivers, but I don't generally crank down very hard on the receiver wrench. Just snug.
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Old May 18, 2017, 11:01   #15
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Adjusting the die until the barrel screws in will allow the receiver and barrel to mate, but really isn't the correct way to fix this. Tapping the receiver is, as you mentioned above.
I would definitely run the die over the barrel, to make sure it's to spec, and clean.
I agree, but if he's using a plug or taper tap, instead of a bottoming one, he won't reach the inside face. The DSA G1 I did this week had the most internal thread incompletely cut, and the relief on the barrel was maybe 1/3 thread shallow. So there was undue torque required at the last 90 degrees. I did a combination of relieving a half thread on the barrel, and bottom-tapping the receiver to get another 1/4 thread cut.
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Old May 18, 2017, 11:30   #16
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I agree, but if he's using a plug or taper tap, instead of a bottoming one, he won't reach the inside face. The DSA G1 I did this week had the most internal thread incompletely cut, and the relief on the barrel was maybe 1/3 thread shallow. So there was undue torque required at the last 90 degrees. I did a combination of relieving a half thread on the barrel, and bottom-tapping the receiver to get another 1/4 thread cut.
I don't know why DSA doesn't fix this issue. And, it's a fix that won't cost them ANYTHING!
If DSA is farming out their work, then the shop making the receivers have fallen down on their contract, and needs to fix this issue. Unless of course, the shop IS making them to print which means DSA has fallen down on the job and needs to revise their prints.

And for the shop making the parts, it's a SIMPLE fix!

As I said before, I'm sure those threads are being cut on a CNC mill, with a threading tool. I've done it a million times! Whoever set that job up, should have taken the time to "tweak" the program or machine parameters, to have that tool go all the way down, and to comp it out to cut the correct threads. It's something that's done with CNC mills and lathes millions and millions of times daily, in shops all over the world!
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Old May 18, 2017, 12:03   #17
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Are the threads cast in, then chased? Or machined. If machined, are they done single-point, or with a tap? I can see if the corner of the leading edge on a tap was chipped, it would leave the innermost thread incomplete but the others fine. But if some form of spiraling single-point cutter, all the threads would be rounded with a worn cutter. What is the normal way of doing a large internal thread on a CNC when the part is not round and concentric to the thread?

I've had to grind my tap back a thread a few times as I chip the leading edge.
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Old May 18, 2017, 12:40   #18
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Are the threads cast in, then chased? Or machined. If machined, are they done single-point, or with a tap? I can see if the corner of the leading edge on a tap was chipped, it would leave the innermost thread incomplete but the others fine. But if some form of spiraling single-point cutter, all the threads would be rounded with a worn cutter. What is the normal way of doing a large internal thread on a CNC when the part is not round and concentric to the thread?
No threads are cast, they are machined in.

First, the part is fixtured in some way. I would either make a custom fixture, or modify something off the shelf, like an angle plate. Something that will hold the forging with the bore straight up.
There's a hundred ways to fixture a part, depending on size, shape, what machining has been done in prior steps, etc., etc.

I'm assuming the forged/cast hole is not round and to size, so an end mill will come down and machine out whatever needs to go.

Then a threading tool is used, usually multi-fluted, especially in harder material.
The tool is programmed to come down in the center of the bore, then spiral out and up at whatever the thread pitch is needed. Usually thread milling on a mill is done from the bottom of the hole, and up.
Here's a link to thread milling and if you scroll down, there's an illustration of how it's done.

http://www.stanleyengineeredfastenin...illing-cutters
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Old May 18, 2017, 14:25   #19
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The Tap I am using is Brownells part # 080-598-982. Not indicated what type of tap it is. The Die I am using is Brownells part # 080-598-151. About tightening the tap, I did try that without a positive outcome. After chasing the barrels I will say that the threads looked better. Not flat but clean and sharp. Unfortunately they still don't work. Although I took metal shop about 50 years ago or so in school I am afraid I am a little out of my league here.

If its the receiver, the thing I find odd is that 308/223s barrels threaded the receiver and timed without problem, and they were Imbel barrels. So, apparently something is different about the threads on these barrels.

Mark, I appreciate you trying you get back with me. Sorry AOL is being a problem. I have received emails from you before so not sure what is going on.

Thanks to all for the replies.
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Old May 18, 2017, 14:37   #20
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The Tap I am using is Brownells part # 080-598-982. Not indicated what type of tap it is. .
That's a plug tap. Here's a link on tap info. Scroll down and you'll see examples of taper, plug and bottoming taps.

https://www.newmantools.com/taps/styles.htm
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Old May 18, 2017, 16:28   #21
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If the V form in the receiver isn't deep enough or the bbl threads are deformed on the top of the V, either is 'fixed by just filing some off the tops of the bbl threads.

Just saying if another bbl went in without issue it is time to examine the difference in does vs doesn't bbls.

There's no real advantage to a thread form that is a pure V tip to valley.
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Old May 18, 2017, 16:48   #22
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If the V form in the receiver isn't deep enough or the bbl threads are deformed on the top of the V, either is 'fixed by just filing some off the tops of the bbl threads.

Just saying if another bbl went in without issue it is time to examine the difference in does vs doesn't bbls.

There's no real advantage to a thread form that is a pure V tip to valley.
Its interesting that you bring this up. I wondered about thread height and whether that may be an issue.


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Old May 18, 2017, 22:25   #23
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Its interesting that you bring this up. I wondered about thread height and whether that may be an issue.


?
Get a good thread gauge and mike the O.D. of your barrel threads. Also, to "tighten" an adjustable die, you back out the adjusting screw... Is that how you did it? Just asking, because if you ran a tap in the receiver, the barrel has to be the issue. Even if your tap is a "plug" tap the barrel should thread in past 2/3's fairly easily.
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Old May 18, 2017, 23:06   #24
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Get a good thread gauge and mike the O.D. of your barrel threads. Also, to "tighten" an adjustable die, you back out the adjusting screw... Is that how you did it? Just asking, because if you ran a tap in the receiver, the barrel has to be the issue. Even if your tap is a "plug" tap the barrel should thread in past 2/3's fairly easily.
OD on one of the barrel threads is .998.

Man am I glad for the dumb noob lesson on the die. I did indeed tighten the adjustment screw thinking I was tightening the cut. I will re adjust , re chase the barrel threads and post the results. As I mentioned my metal shop class was nearly half a century ago.

Regards Sir !

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Old May 18, 2017, 23:24   #25
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OD on one of the barrel threads is .998.

Man am I glad for the dumb noob lesson on the die. I did indeed tighten the adjustment screw thinking I was tightening the cut. I will re adjust , re chase the barrel threads and post the results. As I mentioned my metal shop class was nearly half a century ago.

Regards Sir !

Dean
Imbel tended to just crank stuff down 'til it timed up, I'm betting your threads are "pulled" just a bit, which is why they fit the stub but not your new receiver. Working them down a bit at a time with the die will more than likely fix it.
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Old May 19, 2017, 01:06   #26
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Imbel tended to just crank stuff down 'til it timed up, I'm betting your threads are "pulled" just a bit, which is why they fit the stub but not your new receiver. Working them down a bit at a time with the die will more than likely fix it.
Ok problem seems to be fixed. I feel like popping a Champaign bottle. I readjusted the die and more than chased but less than completely doing new threads. She threads in like a champ.

Times about 10:30 with a snug down but not with a cheater. Not sure if I will have to remove some material from the shoulder or not. Will have to see.

Thank you Sir and to everyone who responded. I am sure I will have more questions.

Just cant wait for the finished product. Got that FAL fever!!
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Old May 19, 2017, 09:23   #27
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So what's the correct die to get for an Imbel?
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Old May 19, 2017, 11:33   #28
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So what's the correct die to get for an Imbel?
All FALs and L1A1s are 1"x16 tpi. (except Izzy, which is M25x1.5, a 60% overlap with 1"x16, and can be chased to fit.)

The issue, I assume, is that there are two kinds of dies. One, hex shaped, is made for cutting threads to the nominal dimension. They often have one side tapered for ease of starting, and the other side at 90 degrees to get proper depth of the last thread. http://www.regalcuttingtools.com/sit...ex%20Die_1.jpg

The other, a split round die, can be "tightened" to make the die cut a tiny bit deeper. There is a screw tangent to split which prevents the die from compressing when locked into the die handle by the set screws. This has to be LOOSENED and then the set screws in the die handle TIGHTENED to make the die slightly smaller.

http://cdn0.grizzly.com/pics/jpeg500...37a58e5e7f.jpg

Tangent screw visible in above image, not in below image.

http://www.practicalmachinist.com/vb...and_dies-7.jpg
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Old May 19, 2017, 16:03   #29
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All FALs and L1A1s are 1"x16 tpi. (except Izzy, which is M25x1.5, a 60% overlap with 1"x16, and can be chased to fit.)

The issue, I assume, is that there are two kinds of dies. One, hex shaped, is made for cutting threads to the nominal dimension. They often have one side tapered for ease of starting, and the other side at 90 degrees to get proper depth of the last thread. http://www.regalcuttingtools.com/sit...ex%20Die_1.jpg

The other, a split round die, can be "tightened" to make the die cut a tiny bit deeper. There is a screw tangent to split which prevents the die from compressing when locked into the die handle by the set screws. This has to be LOOSENED and then the set screws in the die handle TIGHTENED to make the die slightly smaller.

http://cdn0.grizzly.com/pics/jpeg500...37a58e5e7f.jpg

Tangent screw visible in above image, not in below image.

http://www.practicalmachinist.com/vb...and_dies-7.jpg
Yes, I am using the split round I purchased from Brownells. Using it correctly was the key here. I had just received the three screw die stock I bought from Zorro yesterday. Came in right handy. Ya build and ya learn.
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