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Metal barrel sealing tee design

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: )DEMON( » Sat Jul 29, 2006 12:29 am

It aint done yet, there are still lots of things I am going to do. I can't tell you because this is going to be my entry for the build-off :D
Does anybody have any ideas on how I can make a hammer action? The hammer will strike the one way valve (the inside rod opening the diaphram).
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Unread postAuthor: Brian the brain » Sat Jul 29, 2006 4:30 pm

You could try this: ( see diagram)


I've tried something similar in crossbows.
It should work nicely.

Make the parts out of plywood, and sandwich them inbetween two outer layers.Your handle can be placed between the outer layers aswell.

The green dots are the axles(sp) on wich the parts rotate.
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hammer-trigger diagram.JPG
Parts are shown in rest position.The trigger catches in the pizza-slice cut out in the hammer to lock.
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: )DEMON( » Sun Jul 30, 2006 1:34 am

Thanks, I will do that, it will work excellent because I will have a wooden stock. What would be the best material to make that out of? My jigsaw can cut 8mm aluminium.

I will keep you updated on my progress. :D
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Unread postAuthor: Brian the brain » Sun Jul 30, 2006 3:54 am

Inner layer and moving parts should be made of something like plywood.This makes it easier to make a handle and forearm grip of somekind.
The two outer layers that keep it all together should look sweet in 8 mm aluminium.The hammer should be heavy to knock open the valve.You need the momentum.
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: )DEMON( » Sun Jul 30, 2006 5:40 am

What I have made so far should be working except the piston isn't sealing, heres some factors that could be contrebuting to this problem:
1: sealing face slanted
2: washer too hard
3: air escaping to fast
4: I made the spring so that it doesn't push the piston sealed, I am worried it will effect the opening of the piston.

Some how I must solve these problem factors. Anyway heres a progress update.

I got rid off the crappy female quick disconnect and stuck with a schardar valve. I decided not to weld those compression nuts together and instead made the piston housing a bit longer but it shouldn't effect the preformance.
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bits+pieces.jpg
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Unread postAuthor: CS » Sun Jul 30, 2006 5:58 am

F*ck that is nice... Out does most American guns with all these parts to are disposal.

Both 1 and 2 sound very plausible for your problem, although I dont understand 3 or 4. I think I may understand what you mean in 4... Your essentially thinking you dont need a spring in there since your filling from the venting side right? Either way you still need the piston to be spring loaded close. Herm... This may be why one of my pneumatic piston cannons doesnt work. (My dumbass forgot the spring :oops: ) Hopefully that helps.
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Unread postAuthor: )DEMON( » Sun Jul 30, 2006 6:07 am

Yes, it is filled from the venting side so I thought you don't really need a spring but I will make a small one out of piano wire. When I pump air in the piston gets shot forward because it is a few grams, very light. I was thinking of getting a syrindge and taking the rubber face out of it to use as the sealing face, that kind of rubber is nice and soft and not to mention basically the right size. The piston is bigger than the barrel and should work absolutly perfect.
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Unread postAuthor: CS » Sun Jul 30, 2006 6:16 am

Yes, thats what I was thinking. Surely, it will be "shot" forward at first. What happens when you reach your desired pressure? Both sides of the piston will be under the same force and the sealing side needs more force to keep it against the sealing face. Just a quick question... Is your piston housing and barrel the same size?
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Unread postAuthor: )DEMON( » Sun Jul 30, 2006 7:48 am

No, haven't you seen the pics from previous pages?

update**
I made a soft spring out of spring wire. I took the copper piston from befor and I put it in 20mm pvc, this will be the new piston.Solves problem 1.
I tested this by putting a fire extinguisher onto the fill port so I could fill it to a selected pressure instantly. When I did this all the air leaked out from the barrel and small leaks here and there. But I did manage to fire it quickly, it shot a small piece of paper to the other side of the room as fast as a springloaded bb gun. That was just in the first inch of the barrel.

conclusion

Exhaust system and piston work.
Sealing face doesn't seal.
Fire extinguisher can be modified to be used as an air cylinder.

Now for some more pics!
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working..almost.jpg
Fire extinguisher cannon assembly.
new-piston.jpg
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Unread postAuthor: Velocity » Sun Jul 30, 2006 11:03 am

Wow Demon... that is honestly coming together great! I always liked the idea of using copper for small bore barrels... but I never did because I was worried that it would become bent :cry: ... I dont know whether this is true or not.

What is the C:B ratio?
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Unread postAuthor: )DEMON( » Sun Jul 30, 2006 11:08 am

Copper isn't as fragile as you claim, it can take a bump or two. As for the chamber to barrel ratio I am unsure. The chamber volume is a little bigger than the barrel volume. This thing is going to be so fun to shoot! I can't wait.
Any body got any good ideas on sealing faces, it is kind of tricky because of the size.
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Unread postAuthor: )DEMON( » Sat Aug 05, 2006 1:56 am

I got this to the point of perfectly working but then there was leaks that no matter how much epoxy I used to fix, just kept on leaking. As a result I have to remake the piston housing. I suspect that it was the brass rings used to seal the compression fittings, the one on the barrel used a copper ring and it dosn't leak. I found to perfect piston sealing face, flexible and strong, it is a rubber seal for a test tube(from school labs). The piston works perfectly, just as it should, the sealing face being cone shaped (with a flat end) increases the surface area, which is good for a piston. The following images are shown without the pressure gauge.
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new-new.jpg
bit dark
super-piston.jpg
super-piston.jpg (12.67 KiB) Viewed 716 times
piston-housing.jpg
note, lots of epoxy
getting-there.jpg
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Unread postAuthor: MrCrowley » Sat Aug 05, 2006 2:19 am

are brass fittings expensive?im also looking for a good seal in my piston i heard neoprene is the stuff to use but ive got a few rubber disks i might test first.
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Unread postAuthor: )DEMON( » Sat Aug 05, 2006 3:29 am

They arn't that expensive but they cost more than normal fittings.

* I have tracked down the source of the leaking problem. It was the brass rings. They are harder than copper and as a result didn't seal correctly. I am going to buy all the parts to make a new piston housing today.
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Unread postAuthor: Brian the brain » Sat Aug 05, 2006 5:58 am

Sorry I saw this too late.The brass reducer ring needs to be wrapped in teflon too like you found out now.
I really really like this gun now.
It must be a great gun to shoot!!


What kind of excaust valve are you using and where did you get it??
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Can't ask for a better compliment!!
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