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Bertha

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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Bertha

Unread postAuthor: Skywalker » Sun Aug 05, 2007 7:45 pm

We call her Big Bertha, for lack of a better name. And it stuck.

This gun was a joint project between myself and some of my good friends, pictured here.

Image

The barrel is 6' of 1.5" sch40, chamber is 4' of 3", and it has a homemade piston activated by a modded sprinkler valve. It's my biggest project to make, but it went together fast b/c we planned it out.

The piston is made out of 1.25" couplers and endcaps, which allows for easy o-ring grooves. The tee is 2". Notice that the barrel unscrews from the gun to allow access to the piston: I think this is the first gun to use that. The barrel just barely passes thru the 2" male threaded coupler. I thought it would be safer this way than having a threaded fitting at the rear of the piston, since I've had threaded coupler breaks on me twice on smaller guns, once resulting in a nice solid blow to the chest!

I've got no way of gauging the range, esp b/c the potato goes out of sight not long after it reaches the peak of its trajectory. It has quite a kick, even without ammo it still is noticeable. We generally have two people holding it to fire. The best damage we got was a 4" hole in the bark of a big oak tree, plus sticking some large bolts thru old computers.
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Unread postAuthor: mopherman » Sun Aug 05, 2007 7:53 pm

very nice. seems like a very fun cannon.
it seems like you have some ecessive piston travel though.
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Unread postAuthor: Skywalker » Sun Aug 05, 2007 8:00 pm

It's a long piston. It has a endcap at either end, and inbetween there is a male-female threaded connection to allow the piston to be taken apart to service the check valve and piston face. Also, there's a reduction at the end of the piston housing that goes down to 1" pipe to attatch to the sprinkler, that makes the piston travel look longer. And there's a large bumper made out of a blob of silicone caulk. But at least in Jack's book, I'm sure I still have too much travel. Oh well.

PS: we tried using a big chunk of squishy rubber-like gak out of an old 'ergonomic' mousepad as a bumper. It was so flexible, though, that the first time we fired it, it got sucked all the way into the sprinkler valve, and big bubbles of it were coming out the valve! It was pretty wild...
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Unread postAuthor: spud yeti » Mon Aug 06, 2007 8:15 am

Skywalker wrote:Notice that the barrel unscrews from the gun to allow access to the piston: I think this is the first gun to use that.


Is that a first for you, or did you mean spudguns in general? If spudguns in general, it has already been done for quite some time now.
Even so, it still looks like a really good spudgun, well done.
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really good quote/phrase here
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Unread postAuthor: Skywalker » Mon Aug 06, 2007 8:32 am

I'd never seen that on a piston gun before, so I thought I was the first one! Oh well, :oops: I should have learned better than to say something like that, knowing how this hobby works.

But just to be clear, the 2" piston tee is connected to a female threaded coupler at the front, and the barrel goes thru a reducer bushing in the male threaded coupler and extends into the tee. So it's not like a simple exchangeable barrel via threaded coupler, although it does allow exchangeable barrels that way. Once you unscrew the barrel, the piston can slide right thru the tee and the female thread coupler and out of the gun.
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Unread postAuthor: spud yeti » Mon Aug 06, 2007 8:39 am

That sounds really good. I love it when a cannon is properly made, not "ghetto" and sloppy. Are your joints/pipes pressure rated though?
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really good quote/phrase here
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Unread postAuthor: Skywalker » Mon Aug 06, 2007 10:22 am

Thanks! I'm not sure if the reducer there at the end of the chamber is DWV or not. (My friend has the gun right now, so that's why I can't just check and see.)
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