Trust me when I tell you don't want pultruded carbon for this project. The tolerances on that stuff are nowhere near as good as the woven roll wrapped carbon.
I can't find any CF tube that will slip fit over my 12mm OD barrel. Maybe I can find something that would work with some shim stock or something similar.
Quote from: Spacebus on November 22, 2021, 04:13:25 PMI can't find any CF tube that will slip fit over my 12mm OD barrel. Maybe I can find something that would work with some shim stock or something similar.These guys have two type with 0.500" ID, which isn't too far off:https://store.acpcomposites.com/material/carbon-fiber/tubingOf course, they are both pretty thin-walled, just like what I bought. You could always use this, then add another tube around it, should you need / want that. The outer diameter of these is .560 and .594", respectively. You might be able to find something close, or use epoxy to fill, or maybe a bunch of o-rings.- Or use the thick tube Thane used, get the one that's .560 OD, and lightly sand it on the outside. I think that's what I'd do if I were you. Maybe glue THOSE together, then use a very thin o-ring or shimstock between barrel and first sleeve, and then use the moderator for a compression-fit. (Or see what Donny & Thane might suggest, as they have actual real-world experience with this, while I'm still just theorizing.)
I think if I carefully wrap the barrel in aluminum tape the .500" CF tube should just slip right over with a .003" difference in size.
Quote from: Spacebus on November 23, 2021, 08:48:09 AMI think if I carefully wrap the barrel in aluminum tape the .500" CF tube should just slip right over with a .003" difference in size.That's a great idea, since it's easily reversible.The 0.555 tube I bought turns out to NOT go over my 0.552 barrel and it's too thin to try and sand it internally. I mean, I could, but I'd probably destroy it. Internal sanding in general scares me a bit, though I might still try Thane's thick sleeve with the sanding. But otherwise, I think I'll find a tube with a wider ID, and use your aluminum tape idea.
From my five minutes of research aluminum tape is 2.7 mil, or at least the roll I saw on Amazon was.
I don't see how a slip fit no matter how close to diameter would be better than actually bonding it to the barrel. When I sleeved my fx liner. I used 4000psi 2 part epoxy. Not being bonded they can still move within each other. No matter how minute. I'd prefer one sold part.To me it's like having your lug nuts loose....or just tight enough.
Quote from: RDB on November 23, 2021, 11:49:07 PMI don't see how a slip fit no matter how close to diameter would be better than actually bonding it to the barrel. When I sleeved my fx liner. I used 4000psi 2 part epoxy. Not being bonded they can still move within each other. No matter how minute. I'd prefer one sold part.To me it's like having your lug nuts loose....or just tight enough.I'm not sure, myself. - But Thane's idea is that by being able to slide, when you tighten your aftermarket moderator, the moderator tightens the CF sleeve against the breech block, creating a very stiff "outer shell," with the barrel free inside. As was mentioned on that other thread by Rallyshark (I think) , this is how Hatsan gets away with such wimpy barrels. The factory shroud creates the stiffness and protection. I believe folks call this "tensioning the barrel,"because the moderator is threaded onto the barrel, hence "tranferring" that stiffness to the barrel as well.Or something like that.I still think a tight-fitting sleeve, or inner sleeve, is a good idea for minimizing harmonics. With a sliding sleeve, the entire length of the barrel can probably still vibrate slightly.However, it COULD be that a "sliding" sleeve, either lightly touching the inner sleeve or riding on o-rings, might do the same thing as a glued-on sleeve.Heck if I know. Hence this thread. .------------------------------ but obviously, the best of all is to have a glued-on inner sleeve, and then a thick sliding outer sleeve (or replacement shroud) that compression-fits.If I had an expensive gun, and the factory shroud wasn't adequate, I would do that without hesitation. Doing it on a Flashpup, however, might be a little extravagant, though the prices in that Ebay store Thane linked are REALLY good, so it's actually feasible.
......I wouldn't want the sleeve too tight. And I wouldn't be afraid to experiment with the tension. Possibly adding a thick cross section o-ring at one end to compress against.
Quote from: RDB on November 24, 2021, 01:47:35 AM......I wouldn't want the sleeve too tight. And I wouldn't be afraid to experiment with the tension. Possibly adding a thick cross section o-ring at one end to compress against.Yeah, Thane & Donny both made derlin (IIRC) washers for this purpose. I dunno how to do that, but there's probably commercially available ones in the right size.
Personally I believe you are way over thinking this. Epoxy a 1" piece of 18x14mm tube inside the 18mmx20mm tube, Then just use a fender washer. You can put the fender washer between a nut and bolt, check it in a drill and hold a file to it to get it the proper diameter. If you don't have a 18x14 tube then just use blue painters tape. Its only there to center the tube on the barrel. It's not like it's a shroud that needs to be perfectly centered.
Forgot to mention that you don't want to hard couple the barrel to the airtube. That is the opposite of "free floating". The airtube bounces during the shot: It rings in diameter and up and down due to the pressure pulse when the valve opens and slams shut. The bulk stiffness of the air tube is probably higher when the air tube is at max operating pressure, compared to minimum operating pressure, after so many shots.
Forgot to mention that you don't want to hard couple the barrel to the airtube. That is the opposite of "free floating". The airtube bounces during the shot: It rings in diameter and up and down due to the pressure pulse when the valve opens and slams shut. The bulk stiffness of the air tube is probably higher when the air tube is at max operating pressure, compared to minimum operating pressure, after so many shots.A barrel band that attached to the air tube, but has some clearance around the barrel is fine. Then the band prevent the barrel from being tweaked out of position if you bump it.