Liner sleeve

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Rj

Rj

Member
Jan 14, 2017
662
55
Michigan, United States
Wasn't having any problems. But recently saw a post from Ernest regarding it. Shook my head and thought why in the heck didn't I think of that.

If someone is having poi shifts, this may be worthwhile to try. About $20 for glue and carbon fiber. It definitely stiffens the liner up.

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Can you confirm there is no shift in POI or still just a theory. Where you located? Temperature and humidity swings at your location?

From my competitive archery experience there is a limit how much the arrow tube (projectile) can be softened or stiffened for a given length/weight/Kinetic Energy. Something similar shall be applied with airgun tubes (is that a barrel or sleeves) as well, maybe with different wording or different dictionary, but the physics law is a physics law, you over tighten a tube somewhere here/there it will brake somewhere else (ie performance)...Visually look really impressive, but how this can result?

I am learning this as well and open minded to opinions and arguments.
 
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Can you confirm there is no shift in POI or still just a theory. Where you located? Temperature and humidity swings at your location?

From my competitive archery experience there is a limit how much the arrow tube (projectile) can be softened or stiffened for a given length/weight/Kinetic Energy. Something similar shall be applied with airgun tubes (is that a barrel or sleeves) as well, maybe with different wording or different dictionary, but the physics law is a physics law, you over tighten a tube somewhere here/there it will brake somewhere else (ie performance)...Visually look really impressive, but how this can result?

I am learning this as well and open minded to opinions and arguments.
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Big, are you talking about the spine of an arrow shaft? 

There's no pressure applied to the carbon fiber tube in this application. Well...only how much you tightened the barrel nut. Its just stiffening/supporting the liner. Guys have been doing this for years on air rifles and powder burners.

Volquartsen barrels are a good example. 
 
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Loctite 638 bearing retaining compound works great for this purpose. Way less messy than epoxy and easier to use. It fills gaps up to 0.010” (0.020” or 0.5mm on the diameter) which is pretty forgiving. Any sloppier than that, go with epoxy.

The most recent example I did was sleeving a 12mm LW barrel up to 15mm. The carbon fiber worked out perfectly because it brought the OD up to the same as the OEM barrel, adding stiffness without adding much weight, and since the LW barrel was in the white, I didn’t have to go through the trouble to blue it. Matching the OEM barrel diameter was a goal because I wanted to be able to reuse the barrel band, however I cut the barrel tenon for a precise fit to the receiver and combined with the rigidity of the assembly, I ended up not needing the band.

The retaining compound is tolerant of some oil contamination but it’s best if you degrease the surfaces first. Acetone works great. The barrel was pretty smooth so I went over it first with some coarse sandpaper (60 grit) to give the compound something more to bite onto. The ID of the carbon fiber tube was somewhat textured and porous so I didn’t do anything to it but clean it.

Then when I was ready to assemble, I plugged the barrel and put tape over it, squeezed a generous amount of Loctite into the tube, coated the outside of the barrel with a thin film, and then slid them together with a back-and-forth twisting action to help distribute the liquid. Then left it to cure at room temperature for a couple of hours before putting it into the oven for 4 hours at 225F to accelerate the cure. They say 24 hours to fully cure at room temperature, though I expect you could start handing it and machining it after just a couple of hours. 
 
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Stiffness increases with the cube of thickness (diameter). So for example, if you compare a 1/2in barrel to a 3/4in barrel, the larger barrel is just 0.5x thicker but 3.4x stiffer.

The stiffness (Young’s modulus) of steel is around 200GPa. The stiffness of carbon fiber varies depending on the particular construction (chiefly, the fiber orientation) but if you go with a unidirectional type, its stiffness ranges from 180 – 380GPa*, so even the low end of the range is comparable to steel.

So by sleeving a barrel, what you’re doing is taking advantage of a vastly disproportionate increase in stiffness simply by virtue of increasing the diameter, and by using carbon fiber, you get something equivalent to steel with a negligible weight increase.

*source: http://www.dexcraft.com/articles/carbon-fiber-composites/aluminium-vs-carbon-fiber-comparison-of-materials/

 
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Stiffness increases with the cube of thickness (diameter). So for example, if you compare a 1/2in barrel to a 3/4in barrel, the larger barrel is just 0.5x thicker but 3.4x stiffer.

The stiffness (Young’s modulus) of steel is around 200GPa. The stiffness of carbon fiber varies depending on the particular construction (chiefly, the fiber orientation) but if you go with a unidirectional type, its stiffness ranges from 180 – 380GPa*, so even the low end of the range is comparable to steel.

So by sleeving a barrel, what you’re doing is taking advantage of a vastly disproportionate increase in stiffness simply by virtue of increasing the diameter, and by using carbon fiber, you get something equivalent to steel with a negligible weight increase.

*source: http://www.dexcraft.com/articles/carbon-fiber-composites/aluminium-vs-carbon-fiber-comparison-of-materials/
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That would be true if you could truly bond the stiff part of the carbon fiber to the steel. In the CF tubes I've seen the interior is a looser more compressible material. The outer shell is stiff.

I see the barrel moving around...flexing inside the CF tube...even if you add glue (which is pretty compressible as well.) The only way I see this making a big difference is if wrap carbon ribbon/tape directly on the barrel.

It could potentially help damp barrel vibrations.

I would want to see empirical evidence of an improvement in actual performance after adding the carbon shroud. A test that only compares the difference with and without the CF...with no other changes.
 
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Well, you’re making an argument that the increase in stiffness may not be 100% accurately calculable and using it to cast doubt on the efficacy of it. So if the stiffness isn’t 3.4x times higher as in the hypothetical example, but is instead only 2x as stiff, is that so insignificant as to deem it a futile effort?

I mean the evidence is already out there that it helps. Countless examples both in the firearm and airgun world. Less useful for thick bull barrels and more useful for soda straw barrels. It’s also more effective when bedded into the receiver rather than just on the forward portion of the barrel.

Or has Volquartsen and other well-regarded barrel manufacturers just managed to very successfully pull the wool over our eyes? And respected tuners like Ernest Rowe are just carrying the torch. 

BTW, I couldn’t find a reference for the softer interior that you described. I’ll take you at your word though, and if so, that may actually be advantageous in producing a constrained layer setup to help damp vibration. 
 
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Carbon fiber is very strong in tension but when loaded in compression you are really testing the strength of the substrate that holds it together. In order to fully take advantage of those properties it helps to have "wider" structures and more support in compression areas.

I'm casting doubt from the mechanics of making it much stiffer. I'd like to see someone do a before/after bending analysis or even better an accuracy comparison.

I would agree it makes more sense on really thin barrels. I wonder how much would be related to stiffening the barrel and how much dampening if it did...not that the mechanics matter if it helps.



https://www.youtube.com/watch?v=BaSXRoD2xaQ

https://www.youtube.com/watch?v=khJQgRLKMU0




 
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Lol. Really Daniel? If I grab the liner at both ends and it's easy to bow, then bond carbon fiber to the liner and it takes twice the effort to bow it. Did I not effectively stiffen the liner?? Maybe I need my thumbs and elbows calibrated. I'm sorry , but I'm betting engineering background.
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That is exactly the type of before and after I said I'd like to see. That is the definition of empirical evidence. If you notice it doubles the stiffness that certainly is a considerable amount.
 
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