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Author Topic: Adjustable Barrel Tensioner - Harmonics Study  (Read 27749 times))

Offline rsterne

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Adjustable Barrel Tensioner - Harmonics Study
« on: December 22, 2014, 06:56:29 PM »
After reading the idea of using Belleville Spring Washers to tension a barrel on the GTA (thanks, Cal), I decided to draw up something to show how it could be done.... The idea is to thread the end of the barrel (I chose 1/2"-20 NF because that is a common size for barrel attachments) and use 1/2" ID x 1" OD Belleville washers to provide an adjustable tension in the barrel to allow tuning it.... The compression load is taken by a shroud, transmitted to the breech, so the shroud has to be strong enough in compression and the barrel mounted solidly enough in the breech to stand the tension load, which can be considerable.... If, for example, you use 0.050" thick Bellevilles, they have a load when compressed flat of 600 lbs.... A stack of three of them, as shown, has a total travel of 0.075", and since 20 TPI is 0.050" per turn, if you start about hand tight (1/4 turn) and use 1 turn of adjustment, you can adjust the tension from about 100 to 500 lbs.... Here is the general idea....



The red is a bushing in the end of the shroud (blue) to take the load from the Bellevilles, it slides on the barrel (black).... The adjuster (purple) threads on to the barrel, and the Bellevilles are captive inside a chamber for appearance and to keep them clean.... You could have an index mark of the top of the shroud, and a vernier scale around the adjustment collar so that you can return to accurate settings while tuning.... There is a pair of flats machined on the adjuster so that you can use a 3/4" wrench to tighten it.... If you want more tension, just double up on the Belleville stack, (( )) (( to go from 200-1000 lbs. in that same 1 turn of adjustment.... just make sure everything is strong enough.... Different thickness Bellevilles can be used to achieve different adjustment ranges of course.... I think this is worth a try....

Bob
« Last Edit: January 05, 2015, 09:34:12 PM by rsterne »
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Offline hutnicks

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Re: Adjustable Barrel Tensioner
« Reply #1 on: December 22, 2014, 07:47:38 PM »
What exactly is the purpose of the bellevilles as opposed to  simply using the half in thread on fitting and a torque wrench to set the desired tension?
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Offline PakProtector

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Re: Adjustable Barrel Tensioner
« Reply #2 on: December 22, 2014, 08:10:23 PM »
Pretty neat. It poses a certain issue if you want to use the shroud volume for anything. I wonder how much more repeatable the tensioning would be v. the torque wrench.
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Offline rsterne

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Re: Adjustable Barrel Tensioner
« Reply #3 on: December 22, 2014, 08:49:20 PM »
Using a torque wrench would depend on thread lubrication to be consistent or the tension would vary for a given torque setting.... Also, the torque would be under about 100 inch-lbs. for a 1/2" OD dry thread (less if lubricated), that represents about 1000 lbs. tension.... so a torque wrench in ft.lb. would not be accurate enough....

Yes I realize it doesn't allow using the shroud volume, but you can't really do that if you are using the shroud to apply barrel tension anyway, right?.... The choice between accuracy and quiet is easy north of the border anyway, all guns have to be noisy....

ADDITION: From QVTom, he thinks about 800 lbs. tension worked on his .30 cal Rainstorm, so we probably need the double Belleville stack, giving 200-1000 lbs. adjustment over 1 turn....

(( )) ((

Bob
« Last Edit: December 22, 2014, 08:57:38 PM by rsterne »
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1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline hutnicks

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Re: Adjustable Barrel Tensioner
« Reply #4 on: December 22, 2014, 11:24:55 PM »
I'm just thinking that shot cycle vibrations and bellevilles are going to lead to oscillation in the tension value during the shot.
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Offline rsterne

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Re: Adjustable Barrel Tensioner
« Reply #5 on: December 22, 2014, 11:38:13 PM »
The goal is to find a tension that improves accuracy.... If you can't find it, what are you out?.... a few dollars and a bit of work.... It's sure a lot cheaper than another barrel, IMO....

Bob
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Offline Rescue35

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Re: Adjustable Barrel Tensioner
« Reply #6 on: December 23, 2014, 07:51:53 AM »
Nice design and cad work Bob. I will save this one to my best of bob folder. The best thing about winter is that you have more time for r&d.
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Offline Rdsail

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Re: Adjustable Barrel Tensioner
« Reply #7 on: December 23, 2014, 11:22:03 PM »
Nice. I might be doing something with a new mrod barrel. I might conserder something like it

Offline Cal

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Re: Adjustable Barrel Tensioner
« Reply #8 on: December 24, 2014, 12:56:29 AM »
What exactly is the purpose of the bellevilles as opposed to  simply using the half in thread on fitting and a torque wrench to set the desired tension?

To my thinking,  Temperature and "conditions" compensation is the big plus to using a known compliance element in the tension. (cone washers)
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Offline William

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Re: Adjustable Barrel Tensioner
« Reply #9 on: December 24, 2014, 01:31:53 AM »
So Bob,
 When pressure is applied, is it just pulling on the barrel, kind of like its trying to stretch it? Which I would guess keep a constant pressure on it and keep down certain vibrations and such!

What I see is, the shroud is secured to the other end of the barrel or the breech and the Belleville Spring Washers are pushing or compressing against the shroud and in turn the adjuster on the muzzle is pulling on the barrel!

I think I see the concept now, and looks like a rather good one at that!

Took me a minute, but I got it...it's a barrel stretcher  ::)

William
« Last Edit: December 24, 2014, 01:33:47 AM by William »
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Offline rsterne

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Re: Adjustable Barrel Tensioner
« Reply #10 on: December 24, 2014, 02:02:35 AM »
YUP!.... stretch the barrel by pushing on the shroud.... barrel in tension, shroud in compression, loads at the other end taken at the breech....

I agree, Cal, using the Bellevilles will provide a much more uniform tension than just torqueing, over a wider range of temperatures.... without them, differences in the rate of expansion could nearly eliminate all the tension on the barrel if the barrel expanded more than the shroud.... That's another good reason not to just use a single Belleville, a small change in length would change the tension 3 times as much as having 3 of them.... That is also a good reason to use the "softest" Bellevilles you can for a given amount of tension required.... If you need 400 lbs. of tension and you use 3 Bellevilles that can provide 600 lbs. in 0.075" of travel you will get a much smaller change in tension than you would if you used 3 stiffer Bellevilles that can provide 1335 lbs. of tension in 0.054" of travel (the next ones stiffer).... If you get a relative length change of 0.005", the tension on the 600 lb. Bellevilles will change about 10% (40 lbs.).... but with the 1335 lb. Bellevilles it would change over 30% (125 lbs.).... With no Bellevilles, it would change even more, of course....

Bob
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1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline michaelthomas

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Re: Adjustable Barrel Tensioner
« Reply #11 on: December 24, 2014, 02:05:33 AM »
Hi Bob,

I have found that removing even a small amount of material (threading) from the OD of most barrels will open up the ID.  Don't know if that is an issue with your barrel or not.......just mentioning it, as the muzzle can be a bad place to loosen things up. 

Mike


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Offline rsterne

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Re: Adjustable Barrel Tensioner
« Reply #12 on: December 24, 2014, 05:24:52 PM »
I'll watch that, thanks....

Bob
  • Coalmont, BC, Canada
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Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline Smoketown

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Re: Adjustable Barrel Tensioner
« Reply #13 on: December 24, 2014, 07:43:01 PM »
Turning the OD of  a barrel could cause the bore to open up on a barrel that was previously shooting accurately.

Now, are you going to 'single point' the barrel threads or use a 1/2 die?

Depending on the wall thickness, using a die can actually add choke to a barrel.

Just throwing that out there ... And watching the developments closely.

Cheers,
Smoketown
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Offline rsterne

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Re: Adjustable Barrel Tensioner
« Reply #14 on: January 01, 2015, 10:20:18 PM »
Just an update.... I have ordered some Bellevilles from McMaster Carr, and also some tubing to try out this idea.... I will be using my Disco Double as the test bed, using a 1/2"OD TJ's barrel in .25 cal and 1" Bellevilles.... and a .22 cal Crosman barrel (the usual 7/16" OD) with 7/8" Bellevilles, and a piece of 7/8" OD x 0.058" wall 6061-T6 aluminum tubing for the shroud/compression member.... I am sleeving the 7/16" Crosman barrel up to 1/2" to fit the breech and I will be using at least three 10-32 setscrews in drilled pockets to hold the barrels in place.... The barrels were already threaded with 1/2"-20NF and 7/16"-20NF threads for air strippers.... I'll report back when I have some results one way or the other.... 

Bob
« Last Edit: January 01, 2015, 10:22:49 PM by rsterne »
  • Coalmont, BC, Canada
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Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline Tomg

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Re: Adjustable Barrel Tensioner
« Reply #15 on: January 05, 2015, 11:53:55 AM »
I am doing this, with a slightly larger shroud, the pusher nut (threaded piece on the muzzle) have been drilled with 8 holes through to the shroud cavity between the breech and muzzle. But essentially do the same thing as you've outlined in your first post Bob, and it works.
So with some careful planning you can utilize the shroud as intended, while still using it as a ram against the breech to put tension on the barrel.


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Offline rsterne

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Re: Adjustable Barrel Tensioner
« Reply #16 on: January 05, 2015, 03:56:19 PM »
Curious as to how you get the air past the Belleville Washers?.... They are typically at least twice as large OD as ID, so for a 1/2" barrel at least 1" OD.... That works great for pushing on a 1" shroud, not so good for allowing air into it....

I have the .22 cal Crosman barrel mounted on my Disco Double, and tethered it to a regulator at 1800 psi, fed from a SCUBA tank, so the velocity is stable (1% ES).... I had to back off the hammer strike a LONG ways before the velocity dropped from the plateau at 1070 fps with 18 gr. JSBs, but now have it shooting at 1000 fps, and I can dial it down to 600ish with the port restrictor.... I've noticed some interesting things going on with the POI as I change the velocity with just that 24" barrel free floated.... I'll report on that when I do my baseline testing....

Bob
« Last Edit: January 05, 2015, 03:59:45 PM by rsterne »
  • Coalmont, BC, Canada
🇺🇦 Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦

Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline QVTom

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Re: Adjustable Barrel Tensioner
« Reply #17 on: January 05, 2015, 04:08:53 PM »
Hi Bob,

I have found that removing even a small amount of material (threading) from the OD of most barrels will open up the ID.  Don't know if that is an issue with your barrel or not.......just mentioning it, as the muzzle can be a bad place to loosen things up. 

Mike




I've threaded quite a few TJ liners in 22 30 and 35 caliber, all  are 1/2" OD and have not observed and change in bore diameter (measured with gauge pins).  I use a 1/2-28 thread with a full profile insert in the lathe.

Tom
« Last Edit: January 05, 2015, 05:53:45 PM by QVTom »
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Offline Tomg

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Re: Adjustable Barrel Tensioner
« Reply #18 on: January 05, 2015, 05:43:23 PM »
Bob, I dont use washers, so your point is well taken.

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Offline QVTom

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Re: Adjustable Barrel Tensioner
« Reply #19 on: January 05, 2015, 05:57:03 PM »
I like the washer idea too.  I'm glad Bob is taking the lead on this idea.......  By using a steel shroud I've minimized thermal expansion effects but a nice light carbon or aluminum shroud would sure shed a few ounces.

Tom 
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