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Old 11-07-2017, 01:43 PM   #1
doyenofcastle
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strengthen by carbon fiber

Hi guys ,

I have build thin roller speargun and the area where the pulley fix need to be reinforced ,I have search for the CF specs but can't decide which one I need , what thick and directional of the CF ,there is a lot of terms need to know before ordering the accurate CF sheet ,any ideas will be appreciated ,I search in the forum but no one will say clearly what he used .
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Old 11-08-2017, 12:52 AM   #2
Diving Gecko
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Re: strengthen by carbon fiber

For your use, pretty much anything will do. You are not looking to build an F1 car nor a super light bike, so forget about unidirectional fiber.
Thicker cloth can be less malleable, thinner ones are generally more flexible but the kind of weave has a lot to say, too. We are not talking about the strength here but about how easy it will be to lay down the fiber on a part (your gun) and have it drape tightly over varying curves and shapes.

I would probably go for a 2x2 twill weave fabric in about 300grams. Twill tends to be easier to drape over curvy parts and I like the look, too.
BTW, as a handy rule of thumb, the thickness of a cloth relates roughly to the weight in this way: 300g/m2 tends to be about 0.3mm thick, 600g/m2 is around 0.6mm thick and so on.
I would think 2-3 layers of 300g CF would do the job. More wont hurt but probably wont really be needed.

It is often better to build your thickness from layers of thinner cloth instead of trying to make a thicker one fit when it wont. Also, don't be afraid of cutting the cloth into smaller pieces or cutting reliefs in it. In theory, you get slightly better strength from doing all the layers in one go but for our purposes you wont be able to tell a difference, so if it makes it easier just start with one layer. Then add on that after it has cured.

As for the epoxy, get a slow hardener. It gives your more working time which is great when first starting out.
Ideally, you will need to find a to way to compress the fiber onto the gun, especially if there are undercuts or concave areas. Vacuum bagging does the job well, but is a bit of next level. If you post a few pics of the area you want to reinforce, we can advise you better.

As a side note, I don't recall seeing anyone ask specifically which CF a builder used, so if the question wasn't asked, perhaps that's why it wasn't answered. Also, there are so many ways to achieve the same goal when it comes to reinforcing with CF and furthermore it is not uncommon to use more than one type of cloth in a build.

Last edited by Diving Gecko; 11-08-2017 at 02:14 AM.
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Old 11-08-2017, 01:40 AM   #3
JJohansen
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Re: strengthen by carbon fiber

Thanks, I was looking for this info as well. I just can't get my head around how CF seemingly wraps around 3d shapes without bunching up? On really nicely done guns, I don't even see seams. For example, I would like to reinforce the handle area of a big rear handle, but have no idea how to lay the cloth properly. Searched YouTube with little success
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Old 11-08-2017, 02:06 AM   #4
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Re: strengthen by carbon fiber

There should be lot of tutorials online for general composites work, though probably little to nothing for speargun CF work. That's fine as the general techniques are quite universal.
You can start by looking for Easy Composites. They are a UK reseller who rebrands and marks up a lot of products, but they do carry good stuff and their tutorials are not bad at all. Some of the earlier ones should be good for beginners, though I haven't looked in a long time:
https://www.youtube.com/playlist?lis...B0UsKNIuKO9xLb


This kid has evolved like crazy, too but again maybe something suitable in his earlier vids:
https://www.youtube.com/channel/UCQf...vYfx-HHKCbmq9A

Fibreglast is another reseller with a youtube channel:
https://www.youtube.com/channel/UCXP...4WC1WiLZ12eJjQ

And then just keep an eye on the videos that pop up to the right hand side in youtube, there will be many DIY tutorials.

The basic technique is called "wet lay up" and then it becomes increasingly more advanced with vacuum bagging, then resin infusion and finally pre-preg.
Start with wet lay up to get the hang of things. Consider moving to vac bagging as soon as you feel ready as it really helps with compacting the fabric. As for the vac pump, you can make one very cheap out of an old fridge compressor.

Last edited by Diving Gecko; 11-08-2017 at 02:16 AM.
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Old 11-08-2017, 11:19 AM   #5
doyenofcastle
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Re: strengthen by carbon fiber

where the white arrows pointing
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Old 11-08-2017, 11:41 AM   #6
deanmc
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Re: strengthen by carbon fiber

Quote:
Originally Posted by JJohansen View Post
Thanks, I was looking for this info as well. I just can't get my head around how CF seemingly wraps around 3d shapes without bunching up? On really nicely done guns, I don't even see seams. For example, I would like to reinforce the handle area of a big rear handle, but have no idea how to lay the cloth properly. Searched YouTube with little success
I used spray adhesive the few times I laid CF on handles and muzzles. Works pretty well for skinning. See my blog post https://aoshunspearfishing.com/blogs...e-roller-build

This is where I learned the technique https://www.youtube.com/watch?v=aqwhcfQZT8U
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Old 11-09-2017, 02:21 AM   #7
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Re: strengthen by carbon fiber

Great looking guns! Did you skin the handle in halves as shown in the video? They didn't really spend enough time showing how to neatly create the joints. I'm thinking of using a short length of CF sleeve slid over the handle.
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Old 11-09-2017, 03:26 AM   #8
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Re: strengthen by carbon fiber

You can use a CF sleeve over the handle ... I have seen this done and it actually looks better than my way of using just CF tape around the handle.

As for adding CF to any gun ... by far the easiest way is to use sleeves. It is not only easier, it also adds CF to where you need it most. It does that because a sleeve will contract and expand according to the shape of the gun. Thus it adds more CF to areas which are thinner and less CF in areas which are thicker. In a speargun the weakness is usually in thin areas ... thus a CF sleeve is a match made in heaven. With sleeves (or any large work of CF) best results are with a vacuum sealing bag. Today, there are vacuum bags shaped into sleeves! So this also has become super easy to deal with.
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Old 11-09-2017, 10:45 AM   #9
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Re: strengthen by carbon fiber

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Originally Posted by JJohansen View Post
Great looking guns! Did you skin the handle in halves as shown in the video?
I used a solid oversized piece. Once I carefully tacked it in place I cut off the excess with scissors. The bottom of the handle I did with a separate piece of cloth.
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Old 11-09-2017, 05:05 PM   #10
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Re: strengthen by carbon fiber

I did this a few years ago to strengthen a friend's gun. Just took some strands out of a woven piece, wetted the surface with epoxy and laid them on. To blend it in and tie the aesthetic back to the rest of the gun, I chopped the strands and laid them on randomly.
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Old 11-13-2017, 03:21 PM   #11
doyenofcastle
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Re: strengthen by carbon fiber

what about this ?


https://www.ebay.com/itm/Carbon-Fibe...QAAOSwx2dYG43s
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Old 11-14-2017, 12:49 AM   #12
Diving Gecko
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Re: strengthen by carbon fiber

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Originally Posted by doyenofcastle View Post
Sure, that'll work. I actually have some of that. Produced locally here in China. I like the looks of it, so bought some for a small project. But the red strands are colored kevlar which doesn't sand well and can be harder to cut, too.
Kevlar is less brittle and has better impact resistance than CF, which is why it is used e.g. for bullet proofing vests and helmets. In a speargun, it might help with the odd knock a gun will take, but that said, I haven't seen CF guns crack. For your use I would keep it easy for now and just go 100% CF; something like this.

I used it for a camera mount, though I sidelined that project for a bit. Here's a pic of the cloth on the balsa core before I brushed on the epoxy and vac bagged it. The cloth is held in place with a bit of spray glue (as others have mentioned above):

Last edited by Diving Gecko; 11-14-2017 at 12:59 AM.
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Old 11-14-2017, 01:30 AM   #13
JJohansen
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Re: strengthen by carbon fiber

That looks great, I see that the part is covered with what looks like one sheet of CF folded in half. When it comes time to finish the seam where the two ends pinch together, how is that done? I've been searching for info in how to cleanly handle the seam areas with no luck.
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Old 11-14-2017, 06:20 AM   #14
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Re: strengthen by carbon fiber

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Originally Posted by JJohansen View Post
That looks great, I see that the part is covered with what looks like one sheet of CF folded in half. When it comes time to finish the seam where the two ends pinch together, how is that done? I've been searching for info in how to cleanly handle the seam areas with no luck.

Yeah, the fabric was cut roughly to shape and folded in half over the core - which had had a misty coat of spray glue. The seam follows the pink line in the pic below:


Once the fabric was laid down, I cut it a bit closer to the part with electrical shears. Kevlar is a bi*&! to cut, but maybe those cheap surgical shears would do the job just as well.

The fabric moved a little once curing in the bag and a few small creases was the result. That and the fact that I got busy with other stuff made me put this project aside for the moment. But hadn't that happened the next step would have been to trim the part down with a sander - again along the pink line - and I think the seam would have looked alright for my use.

On many other parts, there's an overlay of cloth and if there's no fraying of the edge on the top layer it will look like a tight budding seam.
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Old 11-15-2017, 11:48 AM   #15
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Re: strengthen by carbon fiber

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

helpful
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