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First Airgun

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: Alster370 » Thu Feb 24, 2011 5:19 am

I finished the larger chamber yesterday, and I have to say that its much more powerful. Although I think that if could use a small fire extinguisher tank and hide in in the stock somehow so I could maybe set it up for at least 3 shots per fill?

http://s785.photobucket.com/albums/yy14 ... =001-1.jpg

The tape is temporary, as I think getting the performance nailed down should be the first thing, then aesthetics to finish off.

Could someone tell me what the standard thread size is for uk fire extinguishers? im not too sure. :?
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Unread postAuthor: Gun Freak » Thu Feb 24, 2011 5:29 pm

If you're lucky, the threads on the neck might be standard, in which case you can use a standard bushing. But in my case the threads weren't standard so I just modified the existing fitting on the extinguisher.
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Unread postAuthor: Alster370 » Fri Feb 25, 2011 5:31 am

I liked the look of this one :

http://www.diy.com/diy/jsp/bq/nav.jsp?a ... egories%3C{9372015}/categories%3C{9372044}/categories%3C{9382012}/specificationsProductType%3dfire___gas_safety/specificationsSpecificProductType%3dfire_extinguishers&fh_eds=%C3%9F&fh_refview=lister&isSearch=false&_requestid=115086

Are they hard to disassemble?
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 25, 2011 5:45 am

That type of fire extinuisher is usually at relatively low pressure as it's basically an aerosol can, you're better off looking at this type that is safe at whatever pressure a shock pump can generate. You also get a little arbitrary gauge.
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Unread postAuthor: Alster370 » Fri Feb 25, 2011 6:55 am

Yeah that one looks good, I'l see if I can pop down at the weekend and get it.
Does it have the volume for multi shot capability? I would like 3 shots before I have to refill, and the tank would be pressurized to 200psi. It sounds possible in theory because im currently using a chamber with 14mm bore and 24" length and im happy with the power that gives.
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 25, 2011 7:42 am

The problem is that a ball valve is very hard to control for multiple shots. Here's a rather simple design that can be made using basically plywood cams and levers on a wooden plank base.

Pulling the green trigger will open the ball valve momentarily, then a spring will shut it again. Releasing the trigger allows a second spring to reset it (going past the pink pivoting section on the blue cam) and the trigger is ready to be pulled again.

It's not as complicated as it looks and will give you a fair amount of shots, you can tweak it to open more to trade shot count for power.
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Unread postAuthor: Alster370 » Fri Feb 25, 2011 11:02 am

Could I do this out of acrylic? Il have to search around for some strong springs too, as I dont have any.
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Unread postAuthor: Technician1002 » Fri Feb 25, 2011 11:28 am

Acrylic is brittle. Use polycarbonate instead. (Lexan)
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 25, 2011 11:54 am

Technician1002 wrote:Acrylic is brittle.


True, but as long as there are no hammer-type impacts involved in the mechanism it shouldn't be a problem. In the design I posted the only impact area as such is the stop for the blue cam, but considering ball valve friction it likely won't be travelling fast enough to cause damage.

Here's some inspirational examples of the construction you might use:

Image

Image

[youtube]http://youtube.com/watch?v=Oc5_jCHghAM[/youtube]
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Unread postAuthor: nadjatee1996 » Fri Feb 25, 2011 1:09 pm

I have a question similar to that other guys, where can I find a strong spring? Like a pen or something?
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Unread postAuthor: Crna Legija » Fri Feb 25, 2011 1:19 pm

nadjatee1996 wrote:I have a question similar to that other guys, where can I find a strong spring? Like a pen or something?



iv found the jeeps usually have really strong springs to aid in shock absorption, or this place anyway aren't you from china or something, everything is made there you should have no problem finding mats
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Unread postAuthor: Alster370 » Fri Feb 25, 2011 3:25 pm

Not sure if this is a silly question or not but, could I have my shock pump always attached to the chamber? So when my pressure starts dropping after multiple rounds I could give it one or two pumps to restore it to its original pressure?
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 25, 2011 3:32 pm

nadjatee1996 wrote:I have a question similar to that other guys, where can I find a strong spring? Like a pen or something?


Pay attention.

Alster370 wrote:Not sure if this is a silly question or not but, could I have my shock pump always attached to the chamber? So when my pressure starts dropping after multiple rounds I could give it one or two pumps to restore it to its original pressure?


Why not.
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Unread postAuthor: Alster370 » Sun Feb 27, 2011 10:56 am

Just bought the fire extinguisher, it says 16.5Bar in the red area of the gauge so I assume thats the max.

http://s785.photobucket.com/albums/yy14 ... =003-1.jpg

I would dissasemble and empty it but im forbidden until I do some revision for tommorrows exam :shock: . But from rough measurements its likely to be a female 28mm thread.
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Unread postAuthor: Alster370 » Mon Feb 28, 2011 12:02 pm

Sorry for the double post, but I need a quick answer. Ive unscrewed the fire extinguisher and emptied it out. The thread does look like a female 28mm but I what your views before I buy the adapter coupling.

http://s785.photobucket.com/albums/yy14 ... =002-1.jpg

http://s785.photobucket.com/albums/yy14 ... D003-2.jpg

and the coupling required for 28mm to 15mm

http://cgi.ebay.co.uk/28mm-x-15mm-Compr ... _500wt_922
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