suppressor thread adapter - first try ...

wquiles

Well-Known Member
Yes, first try since when I was doing the "last" operation I broke it. Design problem, it was too thin in one area, so I know how to fix it, which means starting from scratch again :headbang:

Okay, here is my host. Handy rifle, cut and threaded by me in my lathe (a project on its own due to chamber side of the barrel assembly!) in 45-70:
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And here is my suppressor, my form 1 45cal, 1.5OD, titanium:
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The barrel was threaded .578-28, which is the standard "handgun" 45cal suppressor thread size (note: I should have threaded it 5/8-24 instead!), but build the suppressor to be used in my 308 Savage which is threaded for 5/8-24, so I needed an adapter. I tried a cheap one from Ebay to see how they did it:
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But I did't like it, so I decided to make my own, based on a left-over 4140 steel piece from one of my guide rods for my air-oil Mega press:
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I looked at my past notes for guidance on how to make the adapter:
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So I measured the barrel/host, and came up with a basic design: go from .578-28 on the barrel to 5/8-24 on the suppressor:
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So I started by facing the part, and try to do as many operations as I can leaving the part in the chuck for concentricity and alignment:
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Then work on the OD, target of .851":
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wquiles

Well-Known Member
Then work on the .578-28 threaded part:
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And then bore to size:
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Do partial threads (enough to make sure it is concentric):
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Test with an existing 1/2" to .578-28 thread adapter:
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I am basically done on this side, so before I turn it around in the chuck, I align everything to the "0" marking on the chuck to minimize runout changes:
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wquiles

Well-Known Member
Do the OD for the 5/8-24 threads, and part to length:
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I also cut the thread relieve area, which is in fact why this part broke. I should have made the overall part like .150-.2" longer, to allow for more metal on the transition from the hidden internal .578-28 thread and this external 5/8-24 thread:
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Threading tool:
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I then did the external threads, but note that I have to end "very" close to that shoulder above:
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I use this dial indicator to help me know when to disengage the carriage. Target is .400". Tool crash is at .415" :rofl:
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short movie so that you can see the carriage speed:


Test fit:
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And after a couple of light passes, great fit:
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I then needed to complete the internal .578-28 threads. This is when the part broke:
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Broken part:
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So, I cleaned up the broken part that mates with the barrel, and made a "thread protector":
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Good news is that know how to do it again. Fairly easy, and instead of being another 3 hours, it will likely a little less.

Live and learn. Now you know what I meant about making mistakes :)

Will
 

Ian

Notorious member
The way I understand it, .578x28 is standard HANDGUN .45, as in .451" groove. 45 (.457") RIFLE threads can be anything, but typically are the same as .30-caliber 5/8"X24. Glad you got it sorted out, I'd have been tempted to re-thread the barrel if there was enough length, considering all the tolerance stacking that goes on between five threaded connections.
 

wquiles

Well-Known Member
The way I understand it, .578x28 is standard HANDGUN .45, as in .451" groove. 45 (.457") RIFLE threads can be anything, but typically are the same as .30-caliber 5/8"X24. Glad you got it sorted out, I'd have been tempted to re-thread the barrel if there was enough length, considering all the tolerance stacking that goes on between five threaded connections.

I am still learning all of this stuff. I updated the thread above to note the thread I used was for handguns, and that I should have used 5/8-24 instead.

I "think" I might barely have enough barrel length left to thread it "one" more time, but at least for me it was a royal pain to find a "fixture" to hold the back of the barrel on the chuck. I definitely don't look forward to doing that again, so I rather try one more time to re-make the thread adapter soon :)
 
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Ian

Notorious member
I hear you. It's all about setup, making fixtures, indicating until you're crosseyed, etc. Cutting a shoulder, threads, and a crown is gravy.

If you have an outboard spider and short enough spindle to be able to indicate the barrel on both ends through the headstock, that would be ideal, but just making another adapter and verifying suppressor alignment would sure be the easiest thing to do.

If you look HERE you can see my inboard spider project and note the suggestion Bill made to make an aluminum insert and tap it into the rifling to drive the barrel during the turning and threading operations. You could make one to pilot in the chamber and swage into the rifling ahead of the throat just enough to center and drive the barrel in the chuck. On the muzzle, support with live center in the muzzle to turn an fresh thread shank, relief, and shoulder, then switch to a steady on the thread shoulder to trim the muzzle back and re-crown, then back to the live center with a brass button for threading, or swap ends with the barrel for threading and run the chamber pilot in the steady and make a muzzle pilot to support the muzzle while you thread (get this...) AWAY from the shoulder toward the chuck like I did on that bull barrel.
 
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Pistolero

Well-Known Member
Ian,
I made a tap-in chamber insert for a 10mm 1911 barrel that I was relieving behind the bushing
seat area at the front. Chucked the muzzle end, and put the chamber insert, aluminum with a slight
interference fit rode on the tailstock live center. Should work the same for the rifle bbl, in
concept, with a muzzle insert for threading the muzzle, accurately centered between the chamber
and the muzzle centers.

Bill
 
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wquiles

Well-Known Member
Today I started the thread adapter one more time:
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Center drill, drill, bore to size:
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Thread:
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Test it before turning down the OD to closely match the barrel's OD:
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Work on OD, and then test fit on barrel (after making index mark against chuck!):
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Work on the other side of the adapter, cut thread relief area:
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wquiles

Well-Known Member
Complete external threads and test against suppressor:
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Test adapter on rifle:
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Make part look more "custom":
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Completed machining of the thread adapter (.578-28 to 5/8-24):
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Clean and apply cold blue:
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Install with high-strength threadlocker:
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Completed at last:
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Looking through the loading side of the barrel, the barrel to suppressor alignment is perfect, unlike the aluminum piece I started with which was slightly crooked to one side and would have cause a baffle hit. So in the end if "was" worth it making my own adapter :)

Will
 
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freebullet

Guest
Fantastic job!

Is that a 6 jaw Chuck?

On the locktite, did that just go on the adapter/bbl? Didn't figure you'd seal the can on.

Really nice work, thanks for sharing.
 

Brad

Benevolent Overlord and site owner
Staff member
That is a 6 jaw chuck. Great for clamping thin wall stock without crushing it. I’m too cheap to own one.
 

wquiles

Well-Known Member
Fantastic job!

Is that a 6 jaw Chuck?

On the locktite, did that just go on the adapter/bbl? Didn't figure you'd seal the can on.

Really nice work, thanks for sharing.

Thank you. Yes, that is a Bison, 6-1/4", 6-jaw, Set-Tru chuck. I bought it back in 2006/7when I migrated from the 7x to the 8x lathe. Looked "enormous" in the small 8x, but about right (if a tad small) in my PM12x36 lathe.

This video is about 5 years old, but the chuck's adjustment is pretty nice - that dial in this video has .0005" spacing, but the needle barely moves:

After the DRO's, this chuck was easily the best investment for my lathe so far. Likely not as good or "solid" as the Bison set-tru, 5" 5C collet chuck, but once adjusted the self-centering is good enough for the work I do, and I like the wider OD operating range of the 6-1/4" chuck over the 5C collet chuck.

Yes, Locktite only on the barrel side :)

Will
 

Ian

Notorious member
What impressed me was being able to re-fixture the part like six times and still have everything line up with the suppressor. I made a 1.5' round bar jig that goes through the headstock and indicates in the 4-jaw and outside spider for turning muzzle devices; it has 1/2x28 threads on one end and 5/8x24 on the other so the tapped/faced muzzle device blank can be screwed on the end and outside-turned/threaded true and in-line with the bore.
 

wquiles

Well-Known Member
I made a 1.5' round bar jig that goes through the headstock and indicates in the 4-jaw and outside spider for turning muzzle devices; it has 1/2x28 threads on one end and 5/8x24 on the other so the tapped/faced muzzle device blank can be screwed on the end and outside-turned/threaded true and in-line with the bore.

Wow, that is a freaking great idea - brilliant. I have not done enough threaded devices, but I can see how that piece (and the setup) would save time and make parts with better alignment and concentricity :)
 

Ian

Notorious member
The jig solves the problem of making sure the inside threads are true to the outside threads (or other features) both axially and radially. Clean up a few inches of the rod between centers on each end, put those clean spots in the chuck and spider, indicate on center, then turn, face, relieve, and cut threads, and every time you put the jig back in the chuck and indicate BOTH ends on center you know the muzzle device will be aligned true on its internal threads. Really handy for short things like suppressor-mount muzzle brakes which are so difficult to get straight in a chuck....especially for ordinary mortals with cheap mini-lathes and chuck jaws that have a lot of flex. ;)

I forgot to comment on your large-radius thread relief, that's an excellent idea for eliminating stress-riser at the base of the threads. Suppressor mass puts a mighty side-load on threaded connections as the barrel whips against them.
 

wquiles

Well-Known Member
I forgot to comment on your large-radius thread relief, that's an excellent idea for eliminating stress-riser at the base of the threads. Suppressor mass puts a mighty side-load on threaded connections as the barrel whips against them.

Thanks much Ian. Given how and I were I broke the first piece, I "fixed" the problem by making the transition from the internal to external threads longer (more metal, although it is hard to see at the end of the internal threads!), by making the ID about 0.5", which is a little smaller than on the first piece (also more metal), and by applying that radius which as you stated gives is a much stronger profile at that "weak" area. I basically went "all out" on this second try as I did not wanted to have to make the adapter a 3rd time :)
 
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freebullet

Guest
I may need one of those eventually. The ar9 is supposedly threaded 1/2x36 & it appears most 9mm cans run 1/2x24 or 28. Nice to see how others are handling those issues.
 

wquiles

Well-Known Member
Went to the range last weekend and was able to try it out with live ammo. Not the "greatest" picture here, but excellent alignment of the suppressor to the bore:
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At the range (45/70 Handi on the left, and the Savage 308 on the right):
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