Wood-Carbon fusion laminate for Invert gun.

[alex25]

Hello, hope everyone is doing fine in this awful global situation. Due to the fact that we are well into the second wave of covid-19 we find our selfs quarantined once again. So I wanted to keep myself busy and build a couple of guns hence some teak is accidentally lying around. Making clear that im not an expert or a Pro, after all thats why im witting here to ask for some advices. I would like to ask if anyone has tried mixing wood and carbon fiber cloth in the lamination process, looking around the internet I have seen that some people do that. One good reason is that this technique adds stiffness to the hole structure as they claim, I have no reason to doubt that but my question is how much thinner the profile of a carbon fused gun can be compared to just a wood laminated gun. And I ask because I would like to know if that procedure is worth putting effort and money, how thin I can go on the gun for example. And I know you will probably tell me that this is depending on some factors like the number and the size of the rubbers the length of the gun the holes for the rollers how many layers would be the cloth in between and what orientation would have etc. But it would be very helpful to have an estimate of that because it is important knowing that the profile in the 1st case could be lets say 4cm and in the 2nd 6cm. This difference is really a big one especially inside the water, the resistance would be greater for the 6cm profile so the advantages for the carbon laminate are greater than the disadvantages. Hope I didn't bored you with all these technical questions and I will try keep you posted on my project.

 

[7BDiver]

This may sound not so fun and lame in comparison to carbon fiber but when it comes to increasing stiffness a very effective stiffener is actually (sand). Sand can be dispersed easily and very zone specific. What it does is act like carbon in steel, it fills interstitial sites and reduces the elastic limit of the wood fibers by effectively shortening them. Just for fun, take some playing cards and sprinkle a small amount of sand between the cards and mash them together simply bound by rubber bands. You will find the stiffness is considerably increased. If you want to use carbon just for the wow factor this article may be more useful is deciding carbon layup methods: Performance properties of plywood composites reinforced with carbon fibers.
https://www.sciencedirect.com/science/article/pii/S0263822320313477

 

[sharkey]

Let’s tackle one concept at a time.
I have been including carbon fibre into gun laminated for 30 years now with confidence. The only issue is how you manage your personal safety around the dust & also it’s increased wear on the tooling.
I try to practice the best safety & also factor in the tooling costs & consider that used in the correct way ( not for aesthetics like some do) it is a valuable addition.
As a foot note, there are now other composites to choose from which when used in the correct locations can be superior to carbon at a fraction of the cost.

 

[sharkey]

I’m running about twenty speargun blanks over a jointer then followed by a thicknesser in about ten hours. If I can remember I will take some photos of the glue lines including the carbon before & after.
I guess the before & after shots of the jointer & thicknesser blades would tell a better story about the real cost of using carbon.

 

[Kodama]

Let’s tackle one concept at a time.
I have been including carbon fibre into gun laminated for 30 years now with confidence. The only issue is how you manage your personal safety around the dust & also it’s increased wear on the tooling.
I try to practice the best safety & also factor in the tooling costs & consider that used in the correct way ( not for aesthetics like some do) it is a valuable addition.
As a foot note, there are now other composites to choose from which when used in the correct locations can be superior to carbon at a fraction of the cost.View attachment 56793

Are you willing to share with us what these composites are and your experience with them?

 

[Kodama]

This may sound not so fun and lame in comparison to carbon fiber but when it comes to increasing stiffness a very effective stiffener is actually (sand). Sand can be dispersed easily and very zone specific. What it does is act like carbon in steel, it fills interstitial sites and reduces the elastic limit of the wood fibers by effectively shortening them. Just for fun, take some playing cards and sprinkle a small amount of sand between the cards and mash them together simply bound by rubber bands. You will find the stiffness is considerably increased. If you want to use carbon just for the wow factor this article may be more useful is deciding carbon layup methods: Performance properties of plywood composites reinforced with carbon fibers.
https://www.sciencedirect.com/science/article/pii/S0263822320313477

I find your statement about the sand intriguing but I wonder how to apply it with laminated so it yields the stiffening effect. I imagine it is not just sprinkled in between.
If you are correct then why is it not really used by others I wonder.

 

[7BDiver]

It is simply just that, the sand in-between the layers makes the composite structure stiffer, the more layers the better the effect. It is increasing the shear strength between the wood and glue bond and reducing flexibility by decreasing the elastic limit. I imagine the natural vibration of the material would be reduced as well, even heavy carbon arrows have oscillation when released. It takes very little sand and works best when the layers are pressed together so the sand lightly imbeds into the wood fiber. I imagine it would be very hard to find any information for the method as searching online results in nothing but endless ways to sand wood. The application is not huge either, people will generally just add more plies, prefer flexibility or switch to fiberglass for strength with less thickness. This method won't increase tensile strength as with composites, just stiffness. If the idea is purely to increase the rigidity, adding a glass or carbon wrap to the outside would be the next best thing as it will increase the second (area) moment of inertia most effectively.

 

[Kodama]

Thanks for the clear explanation. I will try this out for sure. Probably do a black without the sand to compare to.
My thickness planer is going to love the carbon sand combination.....

 

[7BDiver]

Just as a clarification, don't have sand next to the carbon, I have no doubt it would sever those fibers.

 

[popgun pete]

Quartz grains, second only to diamond in hardness is a component of most sands, so the cutting tools will be put to the test that is for sure.

 

[alex25]

Thank you guys for your replies to tell you the truth now I'm more confused than when I asked. In general I hear your advices for additional material that could be helpful in getting the speargun stiffer, but I would say that having never seen anyone doing it, it's kinda dificult to try those techniques described and going by trial and error approach. Mainly because I have the feeling that I would ruin the wood without knowing the ratio of sand or Quartz in the mixture, furthermore what kind of material is it use and by that I mean what kind of density and when it comes to the application how is the procedure done. Do you have to lay one layer of epoxy with the sand or Quartz then carbon then again another layer of epoxy mixture and this probably has to be done 7 or 8 times as the laminates would be that many. And then comes the tool wearing factor that I believe would be Major I think so the factor

 

[alex25]

Of value for money it's going to go to the sky, so even with just carbon fiber it would be on the edge of not worth putting the tools in such a dificult situation, thus I'm leaning towards not putting carbon in between the laminates because I'm not sure i will be gaining lots of stiffnes considering that I have built couple of other diy speaguns and I have no issues.

 

[7BDiver]

If you have any scrap laminates of wood to play with I would just experiment with the effect. 3 or 4 narrow plies that are about a foot long would work well to show the flexibility difference. I would recommend sand, in the ranged of .005"/.5mm size with about 10 - 20 grains per square inch. It is hard for me to guess if the tool would try to cut the sand or pull it out with the wood chip as it goes. If carbon must be used, alternate layers of wood-sand-wood and wood-carbon-wood. The primary idea is to stiffen the wood layup with sand when the luxury of high modulus carbon is not available or cost effective.