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All About Guns What's your weapon of choice, and why? Discuss the beloved speargun here!

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Old 01-10-2010, 06:37 PM   #121
metelin
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Re: Lost wax carbon fiber molding - first gun

nice work as usual jeff, i was wondering if the lost wax method wont work to produce an entire gun including the muzzle and the handle? i realize it's a much more difficult process, i can also see a bigger problem trying to balance the thing. i'm not totally convinced the so called "monocoque structure" where the gun is a single piece like the c4, the trygons and the bluetec is everything it's suppose to be. the argument is if the gun doesn't have any joints it's much stronger and there is no fear of breaks.

i have a bluetec and a trygons, i paid about 750euros each which at the current exchange rate it's about 1100usd, a c4 is about 50-100 euros less. the bluetec i had to glue on a piece of lead on the front of the muzzle to get the thing balanced and the trygons with it's "water ballast" sinks when the tube fill so i had to plug the water inlets and add lead on the outside, my buddies c4 had similar balance problems he had to correct with lead externally. i guess in the end the guns work great but for that kind of money......

i also have a tin man and griswold euro special. it's a 110cm carbon tube with a tapering shape, it has a demka handle and a added on muzzle and of the three, the thing is by far my favorite. having a removable muzzle and handle allows you to balance the gun internally so no ugly lead showing. i admit it lacks the wow factor of the others but it's a work of art in other ways.

what do you think jeff, you want to try a "monoqoque" gun next?

steve

ps sorry i can't find a pic of the jeff and chad's gun.
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Old 01-10-2010, 07:01 PM   #122
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Re: Lost wax carbon fiber molding - first gun

Yes, Its the galvanic corrosion thing. Metal should never be in direct contact with graphite. one exception is titanium. Otherwise use of glass or phenolic insulators is an option. But please understand, those are guidelines for structures that are expected to last 20+ years. One other option might be just to replace the mounting pins that go through the CF wall with titanium pins. But we are talking about a gun that's indestructible. And the extra cost probably is unrealistic.

IMHO CF is a "cool factor" thing. I would be curious to see a duplicate out of s-glass and comparing the two side by side. I really question any benefit of CF over s-glass for this application unless you are looking for a really light gun.

BTW, 3 hours over a BBQ imho is more than enough for a postcure for a gun.

Again, I want to stress that I am not an expert on the subject. Not even close.
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Old 01-10-2010, 08:01 PM   #123
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Re: Lost wax carbon fiber molding - first gun

I wonder what the theoretical rate of corrosion is, and how does the fact that epoxy is pretty much covering everything affect it? I guess I'm saying that carbon fiber has been in use for quite some time and I don't know of any real world corrosion issues.

I don't disagree that glass would do probably do the job in many cases, but stiffness is a real world issue. Even with carbon fiber, as you noted, proper mix of uni and biaxial and curing is important. With glass it would take more to reach the same stiffness in a long, skinny shape like a speargun.
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Old 01-10-2010, 08:14 PM   #124
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Re: Lost wax carbon fiber molding - first gun

I don't think the use of titanium pins would help. The pins are conductive, so that would just transfer the location of any galvanic corrosion to the trigger mech, instead of the pins.

But I think that it's also important to consider the difference between carbon fiber in a resin matrix, and the nearly pure graphite that is used in things like electric motor contacts. Graphite conducts electricity very well. But I had to scratch and prod to get good electrical conductivity in the little experiment that I did. So in this type of construction, I think that there is a pretty limited contact area between the exposed ends of the carbon fibers, and any metal components. In a home made composite, which tends to be a little resin heavy, there is a lot of insulating epoxy getting in the way.

All in all, I suspect that it wouldn't be a problem unless someone spends WAY more time in the water than I do. Remember, the galvanic cell is only complete when an electrolyte is present. So once the gun is out of the water and dry, the corrosion stops until the next time that it gets wet. Even making allowances for the nooks and crannies that may hold water longer, I think this gun will last a long time.

You may have a point about the S-glass. I don't have any experience with it, so I really can't say.
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Old 01-10-2010, 11:15 PM   #125
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Re: Lost wax carbon fiber molding - first gun

Tin, The children of your children's children will be using this gun without issues
if the mech is rinsed every now and than.I have carbon pods attached to my
gun with Ti and 316 button heads going into a 7075 T6core. The gun has been in the sea 1000's of hrs.on a weekly duty cycle for 20 years.
I feel your gun is outstanding for a wet layup.Many like the look of CF as it
increases the aesthetic value in a client that favors a Tech look.
CF can win over glass when a light prepreg autoclaved component
is needed. I love the look and craftsmanship in your fine creation.
All the best, Don

Last edited by Don Paul; 01-11-2010 at 11:10 AM.
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Old 01-11-2010, 02:04 AM   #126
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Re: Lost wax carbon fiber molding - first gun

I agree that the gun should last for a long time. And I hope I don't come across as a critic of your work. In reality I hope that my layman observations contribute to your work in some small way.

My other concern is in your prep between layups. You said that you used epoxy and silica as a filler between layups. Again drawing from experimental avionics, It is my understanding that such filler between laminates is a common failure point and delamination might occur. A better option might be flux, or maybe use carbon fiber strands as a thickener. Or maybe use peel ply to eliminate the imperfections between layups. Than again, your layup is on a small surface and my concern is probably invalid.

Have you considered using waxed Styrofoam as a male plug? After you are done, you can easily dissolve it with styrene. Or maybe 3lbs divinycell and leave it as a core. Divinycell sandwich layup is often used as a spar in a wing and should really add to the stiffness of your gun.

Again, not to reinvent your work, but I have a feeling that you are not done playing with this yet, and might be opened to new ideas for your next project.

Last edited by POL; 01-11-2010 at 02:14 AM.
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Old 01-11-2010, 08:13 AM   #127
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Re: Lost wax carbon fiber molding - first gun

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My other concern is in your prep between layups. You said that you used epoxy and silica as a filler between layups.
If you are referring to the colloidal silica, I used it as a thickener only to fill 3-4 BB sized imperfections after the first short layup where I joined the wax to the wood section. None after that. I agree that you wouldn't want a bunch of that between laminations.

Quote:
Originally Posted by POL View Post
Have you considered using waxed Styrofoam as a male plug? After you are done, you can easily dissolve it with styrene. Or maybe 3lbs divinycell and leave it as a core. Divinycell sandwich layup is often used as a spar in a wing and should really add to the stiffness of your gun.
I did consider it. I chose the wax mainly because it is rigid, and machines very cleanly. The wax is also hard, and doesn't deform when I am clamping from above to force the delrin rod down into the space that will become the track. And lastly, it was cheap, easily available, and can be repaired with candle drippings if you have an "oops".

Foam may work fine, and I would be very interested if someone has played with it a bit and knows the positives and negatives.


Quote:
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I agree that the gun should last for a long time. And I hope I don't come across as a critic of your work. In reality I hope that my layman observations contribute to your work in some small way.
Everything that you've said has been constructive, with an eye towards helping me do this better next time. I appreciate that. That's the whole point of posting the process here, so keep your ideas coming.
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Old 01-11-2010, 09:50 AM   #128
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Re: Lost wax carbon fiber molding - first gun

www.krsuper2.com/ This guy is building an entire aircraft out of Urethane foam sandwich composites. Unfortunately on his on-line manual he does not have any calculations. You might look at the canopy section, and wing spar sections.
I do have some good links to wing spar calculations and construction on my other computer.
The reason I mention wing spars is because they often are designed to carry 1200lbs over a wing span at 4.5G to 6.0G. that's up to 7200lbs and still needs to be very light. And the tested composite beam calculations and concepts are identical to your application.

BTW, don't look at the above site to long, or you might build a horizontal stabilizer instead, and never finish your gun.
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Old 01-11-2010, 03:01 PM   #129
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Re: Lost wax carbon fiber molding - first gun

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Originally Posted by metelin View Post
nice work as usual jeff, i was wondering if the lost wax method wont work to produce an entire gun including the muzzle and the handle? i realize it's a much more difficult process . . .

. . . what do you think jeff, you want to try a "monoqoque" gun next?

steve
Steve,

The lost wax would probably work very well to make a monocoque shell. But I think you would need to step up to vacuum bagging to do a decent job of it. And like you said, it's hard to add ballast.

I like the removable muzzle for the same reasons as you. Easy to add ballast, or play with different designs. I also like a removable handle, because I can easily re-mold the shapelock grip if I want to.
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Old 01-15-2010, 07:43 AM   #130
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Re: Lost wax carbon fiber molding - first gun

it hurts my heart when i see the extra unused length behind the trigger in such beutiful gun

i was going to suggest you to use this method for hybrids, so you can make midhandle gun, but you already thought about it.

im sure the hybrid will look amazing and very much different than what we see these days

and i would reserve a name for it : Hybrid Revolution

Last edited by Misho; 01-15-2010 at 07:55 AM.
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Old 01-15-2010, 08:19 AM   #131
Tin Man
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Re: Lost wax carbon fiber molding - first gun

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it hurts my heart when i see the extra unused length behind the trigger in such beutiful gun
I hear ya, but at least give me a chance to explain. I like to do both freediving and scuba diving. For scuba diving, I have found that I don't like to chest load because all the stuff gets in my way. Just a personal preference, but I wanted this first gun as a hip loader. Also, there are fair tidal currents where I often dive that make a rear handle gun impractical at least for me. And lastly, I didn't want to complicate my first effort by requiring a pushrod and remote trigger.

I would definately like to make a hybrid using similar construction!

Last edited by Tin Man; 01-15-2010 at 11:30 AM.
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Old 01-15-2010, 11:26 AM   #132
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Re: Lost wax carbon fiber molding - first gun

and you know who to call if you need testers
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Old 01-15-2010, 12:48 PM   #133
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Re: Lost wax carbon fiber molding - first gun

LunkerBuster---please to see post #97.
Sorry bro
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Old 01-15-2010, 02:36 PM   #134
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Re: Lost wax carbon fiber molding - first gun

hahaha you are a better choice anyway my friend
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Old 01-19-2010, 04:25 AM   #135
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Re: Lost wax carbon fiber molding - first gun

Ingenious!!! We have some wax at work. I wonder if we have a piece long enough to cut a mold out of it.
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