Carbon Fiber Gun structures

[PigStikr]

Originally Posted by popgun pete

Interestingly C4 line wrap on the left hand side of the gun, whereas most of my guns line wrap on the right...

That's because it is south of the equator

Turns out the strength/stiffness of CF increases as the 'fiber volume' ie the ratio of fiber to epoxy increases. For wet molding resin infusion gives a high fiber volume. Typically for aerospace prepreg is used and cured in an autoclave - a high temp, high pressure oven. All this is pretty standard tech. I have a homemade vac bag setup for molding that works pretty well. Any wet process needs to take into account removal of the excess epoxy. I use a 'bleeder' for that.
The nice thing about a hollow mold is the pretty finish on the outside 'gelcoat'.
I notice in your gun pics that they are using cloth at about 45 deg. fiber orientation. This is a lot less stiff than axial alignment, but probably impossible to mold axially. Graphite fiber is different from glass or kevlar in that it is really stiff such that it is difficult to make it bend around corners. The weave seems a bit coarse to me though. The really nice feature is the 'no joint' construction where the fibers can wrap the whole circumference. Vac bagged parts are molded in two halves that have to be stuck together. Hence the fibers do not cross the joint leading to a large loss in strength.
Typically carbon is used for it's strength and stiffness to weight ratio. I'm not sure if there are any weight benefits except that ballast could be added in strategic locations to 'balance' the gun optimally. Stiffness can be a nice thing but carbon has very little shock absorbing capability albeit the 45 deg weave helps a bit.

[PigStikr]

Another thing to take into consideration is the 'weave' of the cloth. For starters there is a 'warp' direction and a 'weft' direction. If you're sitting there at the loom the 'warp' direction is being fed continuously, and the shuttle going back and forth is the 'weft' direction. Typically the warp fibers are stiffer/stronger than the weft fibers that must wrap over and under them.
In a plain weave the weft fiber bundle goes over one warp fiber bundle and under the next, alternating every row. A twill weave might go over one fiber bundle and under two. There is another type of weave that is used a lot in aerospace called '8 harness satin'. The 8 harness satin weave involves a warp yarn passing under 7 weft bundle, over one fill, then back under 7 and so on. The fill bundle does the same with the warp fiber bundle.
All of these give different directional properties, along with another type called 'unidirectional' which is obvious.
Your gun appears to have a plain weave with what appears to be different warp and weft fiber bundles, hard to tell from a photo.

[popgun pete]

Here is a closer look.

[Diving Gecko]

@pigstikr I think you are making a little bit too much of a deal out of the orientation of that final layer;-)
They are using what looks to be a 12K spread tow which back when that gun was introduced was a "wow, what is that?!" type of weave as almost everything else on the block was 3K (twill or plain) and pretty much still is. Non-Chinese spread tow is generally not cheap so I am almost certain that they only used this one layer of it for cosmetic reasons; to stand out and look cool.
In theory, a 12K weave is actually stronger as the yarn is less compromised - it doesn't have to twist to go over and under other yarns as often as, say, a yarn in a tight 3K weave does. But if they say that's why they used it, it's just sales BS, haha.

I have no clue on the laminate schedule/lay up of the inner layers. Perhaps a bunch of UD and a bit of traditional layers to keep the UD from splitting and to give some torsional strength (which can also be done with UD at non-axial angles). But these guns have such thick walls that the layup doesn't have to be super optimized. It's not a race bike with sub-1mm walls where every ply and its direction is carefully thought through. A CF speargun is still a very crude example of what composites can do and achieve.

[popgun pete]

C4 also make bicycles like this one from a few years ago. Bring plenty of money!
P.S. Looks like they are no longer making bicycles and are now solely into dive gear. The yellow bike is their "Joker" from a decade or so ago, but it looks like a bike from the future.

[Diving Gecko]

Originally Posted by popgun pete

C4 also make bicycles like this one from a few years ago. Bring plenty of money!
P.S. Looks like they are no longer making bicycles and are now solely into dive gear. The yellow bike is their "Joker" from a decade or so ago, but it looks like a bike from the future.

The vast majority of bike brands, including many of the most expensive ones, have their composite frames made in China or Taiwan. C4 was always a tiny mom and pop shop compared to the big brands and I guess they couldn't compete in that market.

[popgun pete]

C4 thought that they were being clever by making a front end that combined a band anchor hole and band elevators into a new design where the power bands were trapped by side struts paired on either side. This architecture hails from the gear lever mounting bosses that used to be on either side of the down tube on a bicycle frame, but here they were in pairs on each side with a metal side plate mounted to bridge the gap and close them off, thus stopping the bands from falling out on a speargun. This is effectively turning the biplane wing band elevators and band holders on an old school JBL muzzle through ninety degrees so that instead of sitting vertical they are now horizontal or laying flat being in line with the barrel axis. Nothing wrong with that, but with the shooting line wrap descending from the top of the gun they didn't add a top mounted front line hook or wrapping pin and that omission forces the shooting line to wrap from underneath the muzzle. With the muzzle side struts just waiting to gobble up the shooting line as the spear powered its way out of the gun they had to make sure that the line always pulled away from under this line snagging structure and that is why it has the two line wrap sequence on each side of the gun that does just that. A downside of this arrangement is rather than a moving spear instantly dislodging the line on the muzzle wrapping pin so that it is gone before any shaft tabs arrive at the muzzle, on the C4 Urukay and Joker the slackening line still has one line wrap to pull out before it gets to pull away the transverse run of line across the spear which if it hasn't developed enough slack will be hit by a shaft tab. Generally it doesn't, but sometimes it may do so.

C4 recommend slotted rather than tabbed shafts for these guns and now you know why.