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Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: bigbob12345 » Sat Mar 01, 2008 11:20 pm

DYI wrote:BBS


what do you mean by that
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Unread postAuthor: DYI » Sun Mar 02, 2008 9:13 am

Bendy Barrel Syndrome.
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Unread postAuthor: bigbob12345 » Sun Mar 02, 2008 9:16 am

Oh yes definatly :lol: Maybey Ill sleeve it in something to stiffen it up.
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Unread postAuthor: DYI » Sun Mar 02, 2008 9:21 am

I think the cheapest method would be to make a support like the one on the carriage part of the SCTBDC's stand (which still hasn't been rebuilt :roll: ). It would kill portability, but you could always use a shorter barrel for shooting up random stuff, and then the 10 footer for damage.
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Unread postAuthor: bigbob12345 » Sun Mar 02, 2008 9:25 am

I use my golf ball barrel to shoot up random stuff but a shorter barrel would be nice.
Maybey ill chop it in half and throw away the other half.
and then just go buy another stick of it or maybey two :roll: to make the CB better.
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Unread postAuthor: SpudBlaster15 » Sun Mar 02, 2008 6:23 pm

Perhaps instead of removing a great deal of length from the barrel, you could remove the current chamber and replace it with a longer, smaller diameter pipe (7' of 1" nominal diameter PVC pipe would give you a similar volume), and use two elbow fittings to bring it flush with the chamber, which would enable you to strap it securely to the barrel, thus creating one solid assembly.

I'm quite surprised that you were not able to penetrate more than 7 empty soda cans with a marble. When charged to 180PSIG, my HV-PBL will fire a paintball through 6.5 cans before breaking up. Even though the muzzle velocity of said PB is nearly 30% greater than that of the marble you fired (approaching the speed of sound in room temperature air), I initially suspected that you would be able to punch through at least 10 cans (perhaps more), due to the tendency of a marble to maintain its integrity when subjected to such impacts.
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Unread postAuthor: bigbob12345 » Sun Mar 02, 2008 6:29 pm

that 1in chamber idea is good but I dont really want such a long chamber this one is fine and it is more sturdy with the larger diameter barrels.

you took your HV-PBL to 180psi :shock: that is pvc you know I dont think that was the smartest thing to do.
And the reason it went through so little is that it was at 80psi at 120 or 140 it will go through a lot more
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Unread postAuthor: SpudBlaster15 » Sun Mar 02, 2008 7:01 pm

I understand that you used only 80PSIG, but with such a long barrel, even this low pressure should produce sufficient acceleration to give the marble a good deal more kinetic energy than is required to penetrate 7 soda cans.

At 140PSIG, I suspect you will be able to punch through more than 10.

The chamber of my HV-PBL is rated to 450PSIG, the barrel 200PSIG, and I have (roughly) calculated the failure pressure of the theoretically least structurally integral component of the valve to be well over 500PSIG. 180PSIG is nowhere near any of those values, so I consider it to be entirely safe. It was also below freezing during the firing session, which further increased the strength of the PVC components.

However, exceeding the 160PSIG rating on my Canadian Tire bike pump caused its pressure gauge to blow apart (again), this time irreversibly.
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Unread postAuthor: Lentamentalisk » Sun Mar 02, 2008 9:23 pm

freezing PVC does not make it stronger... It most definitely makes in more rigid and easier to crack into a million pieces... Next time wait for warmer weather.
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Unread postAuthor: bigbob12345 » Sun Mar 02, 2008 9:28 pm

Actually Lentamentalisk it does.
the colder pvc gets the stronger but yes if you dropped it, it will have a much higher chance of blowing.
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Unread postAuthor: SpudBlaster15 » Sun Mar 02, 2008 9:52 pm

Lentamentalisk wrote:freezing PVC does not make it stronger... It most definitely makes in more rigid and easier to crack into a million pieces... Next time wait for warmer weather.


I'll admit that I should have specified the exact strength property I was referring to, but it should be fairly obvious based on the context of my post.

The tensile and yield strengths of thermoplastics increase with decreasing temperature, but their impact strength is reduced. Obviously the relevant property (so long as I don't drop the launcher) is tensile strength. I was slightly worried about a barrel failure (as it would be subjected to impact stress upon firing), but none such events occurred.
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Unread postAuthor: Lentamentalisk » Sun Mar 02, 2008 9:58 pm

well just wear safety glasses and long sleeved shirt/jacket, and long pants, and hopefully you will be ok ;)

edit: ye gods! I just used a smiley! What is this world coming to?
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