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4 inch piston cannon (lots of pics)

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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4 inch piston cannon (lots of pics)

Unread postAuthor: grock » Sun May 03, 2009 3:09 am

as promised, i went to my uncle's place, and i return with pictures. sorry, you guys got to wait until next week for a video, there was too much going on this week. the design is a fairly simple barrel sealer, with a slightly less simple support system. the plates on the ends of the 4" T are connected by threaded rod to make the piston serviceable, and the barrel interchangeable (right now i have a 3" barrel on there, i plan for a TB and GB one later) the [piston is made out of 2 pieces of solid PVC connected by a 2" PVC pipe. there is a built in check valve. pilot is a 1/4" ball valve, im sure ill upgrade to a sprinkler or QEV eventually. we shot it using the forklift as a shooting stand, and it rocks the forklift a bit. and did i mention that it is my first pneumatic? enjoy.
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Attachments
DSCF0101.JPG
the cannon. theres a spray paint can for size refrence
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DSCF0106.JPG
this is the front of the holder, i will most likely make one with a smaller hole for a smaller barrel
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the back of the back attachment. the ball valve is threaded into the plate
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the front of the back of the holder. the o ring seals against the 4" plug on the back of the T
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this is the 4" plug on the back of the T.
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another view of the back plug. the o ring in the bottom is free sitting, its the bumper
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the piston in my uncle's lathe
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front
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side
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thee cone. the milling lines are a little rough, but whatever. casualty of speed.
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the back of the piston. the hole for the check valve is in the upper left corner. its pretty much a 1/8 npt plug and a sweet custom piece we made
DSCF0128.JPG
the plug
DSCF0127.JPG
the plug and the custom piece. its pretty much a + and a circle
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Unread postAuthor: inonickname » Sun May 03, 2009 3:21 am

Looks great! Big, powerful and well built! What pressures you running it at?

Awesomeness
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Unread postAuthor: SubsonicSpud » Sun May 03, 2009 4:19 am

Wow, this cannon is going to be a monster :twisted: . Good idea with the cone on the piston, It dose increase flow substantially over a flat piston face. Well Done :D

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Unread postAuthor: LCTChamp » Sun May 03, 2009 1:22 pm

Looks good. Can't wait to see some damage pics/vids.
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Unread postAuthor: psycix » Mon May 04, 2009 12:44 pm

Nice! Great machining you did there.
I love the endplates clamping onto the T piece. Thats a great method to have an airtight and secure way to have a serviceable joint.
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Unread postAuthor: Technician1002 » Mon May 04, 2009 12:59 pm

May I ask if there is any reason you left the lathe jaw chucks turned for inside clamping? When I borrow my dad's lathe we turn the jaw chucks around end for end so large diameter flat disks are easier to chuck true against the jaws. Using outer steps the work can be set flat against the next step smaller. The plastic is likely to twist loose in the end of the chuck as shown.

Did you know the jaws are reversible? :?: They are installed as shown in the photo to hold pipe, flanges, and such from the inside or long rods from the outside. It was not intended to hold disks on the outside in this configuration.

I posted this question here instead of a PM for the benefit of the form. It is for those who are learning lathe skills here. Please don't take the question as an insult. It's not intended as such.

To reverse the jaws, open the jaws all the way. They will fall out. Trade them end for end and close the jaws.
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Unread postAuthor: grock » Mon May 04, 2009 2:05 pm

Thanks for the comments. I was just showing the machine we used to make the parts. When we do actual machine work, the parts are held more securely. My uncle says those are reversible top jaws, we have aluminum soft jaws that bolt on to that chuck also.
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Unread postAuthor: mark.f » Mon May 04, 2009 3:18 pm

Wow, that's a unique way to hold the valve together. Also removes some of the design constrictions when simply threading machine screws through the back of the tee and through the <strike>read</strike> rear plug. I like it!

EDIT - geez, I just spent all day writing a research paper which part of includes the "spellcheck is not a substitute for proofreading" argument, and then make a stupid mistake which I am now editing, including this long soliloquy... sorry.
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Unread postAuthor: Moonbogg » Mon May 04, 2009 4:07 pm

Awesome work! How does the cone shape reduce drag? The air won't be gushing toward it will it?
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Unread postAuthor: grock » Mon May 04, 2009 6:38 pm

the cone shape increases flow by redirecting the air away from itself so when the piston moves back, the air does not slam into itself.
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Unread postAuthor: Technician1002 » Mon May 04, 2009 11:24 pm

grock wrote:the cone shape increases flow by redirecting the air away from itself so when the piston moves back, the air does not slam into itself.


Best explained by driving around a square corner and a well banked and rounded one at high speed. Things get shook up much less on the rounded corner. Less energy wasted in turbulence = higher flow efficiency.


http://video.google.com/videosearch?q=cavitation+globe+valve&hl=en&emb=0&aq=f#

Check some of the videos in the google search. It is water flow in a clear valve body to show cavitation. High speed air flow will also produce low pressure areas that restrict flow. Minimising the turbulence improves pressure loss through the valve.
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Unread postAuthor: jook13 » Mon May 04, 2009 11:36 pm

Wouldnt shock heating come into play there though? As in, the cone reduces the shock heating of the air flowing through the valve, thus throwing another variable into the mix.
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Unread postAuthor: Technician1002 » Mon May 04, 2009 11:54 pm

jook13 wrote:Wouldnt shock heating come into play there though? As in, the cone reduces the shock heating of the air flowing through the valve, thus throwing another variable into the mix.


Lower turbulence energy loss is less energy lost as heat. Less energy lost as heat is more energy delivered as work (Ft/Lbs). :D

In GGDT, this is the valve efficiency.
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Unread postAuthor: SubsonicSpud » Tue May 05, 2009 3:38 am

When I first made my 25mm copper cannon, it originally had a flat faced piston. I mucked around with streamlined piston faces and managed to get about a 15- 20% increase in fps with identical projectiles and pressures, so it definatly has a great effect on performance.


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