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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: psycix » Thu Jul 10, 2008 5:53 am

If you are going to rip the back apart, then why dont you first try to slap on a BV?
And why decrease the porting if you can also increase the piston diameter.
Instead of a syringe tube, just use a piece of pvc (or any other pipe) or even just make it like any co-axial where the piston has the same diameter as the chamber.
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 10, 2008 12:27 pm

psycix wrote:If you are going to rip the back apart, then why dont you first try to slap on a BV?
And why decrease the porting if you can also increase the piston diameter.
Instead of a syringe tube, just use a piece of pvc (or any other pipe) or even just make it like any co-axial where the piston has the same diameter as the chamber.


A ball valve will still need a schrader attached somewhere for filling, not as straightforward as it looks. I'm trying to source a section of pipe midway between the chamber and the barrel in order to cast another piston.
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Unread postAuthor: POLAND_SPUD » Thu Jul 10, 2008 12:59 pm

A ball valve will still need a schrader attached somewhere for filling, not as straightforward as it looks. I'm trying to source a section of pipe midway between the chamber and the barrel in order to cast another piston

you can use a threaded male quick connect fitting

EDIT
pic added
http://www.chromate.com/NC%20STATE%20CO ... -16381.jpg
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Unread postAuthor: THUNDERLORD » Thu Jul 10, 2008 3:00 pm

Looks clean/simple like a combustion JSR.
I kind of understand your building strategy too.
I was wondering about triggering a larger piston by shraeder valve and a simple lever trigger to depress the pin before.

How about a burst disc piloted piston?
I was thinking a threaded piece could be used and a new burst-disc threaded on before each shot maybe.
The trigger would be a sharp piece to puncture the disc(?) 8)
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 10, 2008 5:48 pm

The thing is that if you're going to bother with the hassle of a burst disc, you might as well use it as your main valve and get much better performance than any piston valve could offer.
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Unread postAuthor: THUNDERLORD » Thu Jul 10, 2008 6:43 pm

A ball valve will still need a schrader attached somewhere for filling, not as straightforward as it looks. I'm trying to source a section of pipe midway between the chamber and the barrel in order to cast another piston.


What about removing the internals of the shrader, Attaching a hose and clamp over it.
Then other end of hose into a hose barb nipple, threaded into a blow nozzle.
For filling, you could plug into the output of the blow nozzle (somehow)and depress the valve on blow nozzle till full? (forgot to ask earlier) :roll: 8)
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 11, 2008 9:53 am

It seems a solution is at hand, I... "borrowed" a 250mL plastic measuring cylinder that's midway between the barrel and chamber diameter which will make a nice piston tube, as well as a rubber flask seal that - with a bit of epoxy assistance, of course - should make a decent piston.

I'll have a play over the weekend and hopefully pull this project out of the inexorable depths of fail :roll: :D
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Unread postAuthor: THUNDERLORD » Fri Jul 11, 2008 10:47 am

jackssmirkingrevenge wrote:The thing is that if you're going to bother with the hassle of a burst disc, you might as well use it as your main valve and get much better performance than any piston valve could offer.


I've been thinking of adding a burst-disc in front of a sprinkler valve.
Probably won't be as good as a burst disc alone, due to the curved air movement inside the sprinkler valve. But should improve perfomance(?).

Also JSR, I've been thinking up a knife with a tube (barrel) as handle, and the knife has another tube, (like normal dagger only hollow handle),containing pressure.
And a burst disc at bottom. So either when it strikes something, the disc (inside bottom of handle) will rupture, fires the blade into whatever.
I want to design a trigger also that will press the burst disc to rupture it and shoot the blade through air also!!!

Got the idea off a spring powered military one that was banned but they still sold it without the spring.(can't find it now).
Found this though:http://www.youtube.com/watch?v=9BXy_8rb6_w&NR=1 8)
And this law from Maryland :( "§ 4-105. Transfer of switchblade or shooting knife.
(a) Prohibited.- A person may not sell, barter, display, or...
(2) a device that is designed to propel a knife from a metal sheath by means of a high-compression ejector spring, commonly called a shooting knife.
(b) Penalty.- A person who violates this section is guilty of a misdemeanor and on conviction is subject to imprisonment not exceeding 12 months or a fine of not less than $50 and not exceeding $500 or both.
This will make the price more expensive :P 8)
BTW, I could make a sketch for new post, but not much time today. :wink: 8)

EDIT: Holy crap, just re-read the legal jumbo and it's got "compression spring", (Nothing about compressed co2) IDK :roll:
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 11, 2008 11:20 am

THUNDERLORD wrote:I've been thinking of adding a burst-disc in front of a sprinkler valve.
Probably won't be as good as a burst disc alone, due to the curved air movement inside the sprinkler valve. But should improve perfomance(?).


It should, but a simpler way of doing it would be to have a breech that is tighter than your barrel, avoids having to change disc every time while still delaying projectile motion enough for the valve to open fully.

Also JSR, I've been thinking up a knife with a tube (barrel) as handle, and the knife has another tube, (like normal dagger only hollow handle),containing pressure.
And a burst disc at bottom. So either when it strikes something, the disc (inside bottom of handle) will rupture, fires the blade into whatever.
I want to design a trigger also that will press the burst disc to rupture it and shoot the blade through air also!!!


See attached diagram, I think I get your drift ;) Though we're drifting away from spudguns as a hobby here, grey area.

Personally I think that knives that fire their blade are a bit silly - the great thing about a knife is that it never runs out of ammunition, why would you want to throw it away?

The GRAD 22 revolver in that video makes a lot more sense. My personal favourite is the Russian (obviously :D) NRS shooting knife, single shot but it fires a special silent cartridge without the need for a suppressor.

In the meantime, I'm casting a larger piston for the subject of this thread, hope to have some results by Sunday evening :)
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Unread postAuthor: THUNDERLORD » Fri Jul 11, 2008 12:10 pm

Thanks JSR, Lots of reading/info in those links!
I've gotten off topic, but it's stuff I came up with replying here/ thinking of piston solution ideas. (strange how that works).

You got my idea, But how I was thinking, the burst disc would be on end where the shrader is shown and all parts in diagram one piece.
Then fitted inside another pipe for the external handle.
That way it could be retrieved and used as a knife. (maybe not good idea...)
Also there'd be a safety pin so it could be used as knife until whenever someone wanted to shoot it.
More of a novelty I guess (I had your same thoughts about the spring version).

Thanks for the info. I was wondering how the heck that knife gun worked.
My friends .22 that size goes through 2+ thick phonebooks.
That would be a cool bayonet! :twisted: :wink: 8)
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Unread postAuthor: psycix » Fri Jul 11, 2008 1:12 pm

A ball valve will still need a schrader attached somewhere for filling, not as straightforward as it looks. I'm trying to source a section of pipe midway between the chamber and the barrel in order to cast another piston.

Well, use a tee with the BV on one branch and a schrader thingy on the other. Why not try it, since it may already get the failed gun working?
If you want an efficient gun, then use a proper pilot valve, and not a schrader.

IMO, you could be better of simply using the chamber diameter as piston diameter. It will mean you wont have to center the piston sliding tube.
The extra piston weight will not be a worry due to the increased surface area, and epoxy cost isnt going to increase if you just use an end cap (preferably threaded) at the end. Tap in the pilot and schrader.
OK, your pilot volume will be increased, but that isnt something to worry about if you use a proper pilot valve.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 11, 2008 1:54 pm

THUNDERLORD wrote:That would be a cool bayonet! :twisted: :wink: 8)


Already done mate ;) though of dubious value considering it's attached to a rifle many times more powerful than the humble 22.

Image

psycix, thanks for the advice but already hacked it up and making a new piston, I'll let you know how it goes ;)

edit: the final epoxy "sitting" has been poured, results will be in within the next 24 hours, so fingers and all other available bodily appendages crossed. It had better work, I barely have enough epoxy left to make a small pengun hehe
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Unread postAuthor: THUNDERLORD » Mon Jul 14, 2008 9:56 am

jackssmirkingrevenge wrote:
THUNDERLORD wrote:That would be a cool bayonet! :twisted: :wink: 8)


Already done mate ;) though of dubious value considering it's attached to a rifle many times more powerful than the humble 22. ...


I thought it looked like a bayonet in the vid!
Well, the average soldier (with m-16) carries six 40 round magazines. (seven if they can get one) (3 ea. pouch one in rifle) That's usually about 260 rounds.
So "one shot one kill" is usually prefered when extra ammo's not nearby and the three shot bursts are reserved for shooting at groups or armor/ aircraft (concentrated firepower).
So the bayonet having some shot reserve capability is nice.
Also it gives each troop a sidearm.
But the other value I see it having is that, an advantage of the knife besides never running out of ammo, is that it is silent. And to silence the smaller caliber of it would require a smaller silencer it could be fitted with also maybe. :twisted:

Seems off-topic but my mind was thinking JSR-burst disc(some reason). Then the Piston problem- burst disc triggered piston(?). Then burst-disc triggered by sharp object. Then I inverted and had burst-disc fired knife!!! (and I remembered the old spring knife said to have 7 times more penetration than using muscle power. (funny how that works).

... I barely have enough epoxy left to make a small pengun hehe

:lol: I was wondering how it's coming along. BTW New pengun? 8)
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 14, 2008 11:11 am

THUNDERLORD wrote:I was wondering how it's coming along. BTW New pengun? 8)


Back on the truck of fail I'm afraid, the piston is refusing to seal and I've run out of glue so there's no point in taking it apart. I'll be back home in the beginning of August though, I'll pack more epoxy then.
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Unread postAuthor: psycix » Mon Jul 14, 2008 4:18 pm

Failed again?!
*sigh*
Seems like having 6210 posts on worlds largest spudgun forum doesnt mean you can build em.... :P

Some tips for the next try:
-use bushings/reducers where you can in order not to use an exessive amount of epoxy, and having stuff straight n centered.
-use a goddamn pilot valve (a schrader is not a pilot valve unless the piston is really small, applying to pen guns)
-When relying on small pilot valves, make sure to use o-rings, I am not sure how well your casted pistons hold back air, but I high doubt their airtightness (one with proper o-rings that is airtight CANNOT leak chamber stuff out of the pilot)
-The piston sliding tube has to be 100% inline with the barrel for a proper seal. A tube that is connected to the chamber using a casted epoxy bushing is very hard to get perfectly straight and centered, same goes for the barrel. And why not use the chamber wall itself as sliding tube? Large diameter piston makes sure there is enough frontal area.

Better luck next time :)
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