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Getting ready to build a modular cannon, non-coax/coax...

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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Getting ready to build a modular cannon, non-coax/coax...

Unread postAuthor: jeepkahn » Tue Jan 27, 2009 4:59 pm

I'm getting ready to build a gum that will be for all intensive purposes, an inline chambered coax, or not( I'm not sure it's still considered a coax if the barrel doesn't enter the chamber)...

It's going to be a 4"x24"long chamber that will use a barrel sealing piston valve that will be a 4" 100% sealing disc/with checkvalve on one end of a 24"threaded rod, and a 2" disc with a barrel sealing face on the other, the 4"x 2" bushing on the barrel side will have a 2" female camlock screwed in, and the interchangeble barrels will all be fitted with male camlocks, they will be 3"x 60", 2.5"x 60", 2"x 72", and 1.5"x 72", and a 72" GB barrel. One thing that I will be doing is at the sealing end,I have a friend who is going to machine a 4" down to 2.375" velocity stack out of pvc that will be installed at the barrel end of the chamber, and the pilot will be the 3/4" qev that I ended up not needing on the GB cannon...

What's the thoughts on the velocity stack and the inline layout(for making the barrels interchangeable), and would this be considered a coaxiel or a chambered or a chamber sealing or a barrel sealing???
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Unread postAuthor: john bunsenburner » Tue Jan 27, 2009 5:12 pm

Maybe you go something wrong: You need the barrel entering the chamber for a barrel sealing piston to work, there are afew little exeptions like the thing i am building on now. Look at: Piston valves explained vissually, it will help you unserstand. If this is your first gun then it might be a little difficult to achieve your goals. Oh and i recomend you get GGDT its a simulation software that shows you the velocity and mayn other useful things that your gun will have. Oh and if i where you i would try and either work on my spelling a little but more, proof read my posts and use the spell chack botton. After all i didnt know we where making candy here:
I'm getting ready to build a gum will be for all intensive purposes
:wink:
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Re: Getting ready to build a modular cannon, non-coax/coax..

Unread postAuthor: starman » Tue Jan 27, 2009 5:29 pm

jeepkahn wrote:I'm getting ready to build a gum that will be for all intensive purposes,


Maybe you mean.... a gun that will be for all intents and purposes..... :wink:
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Unread postAuthor: jeepkahn » Tue Jan 27, 2009 6:17 pm

john bunsenburner wrote:Maybe you go something wrong: You need the barrel entering the chamber for a barrel sealing piston to work, there are afew little exeptions like the thing i am building on now. Look at: Piston valves explained vissually, it will help you unserstand. If this is your first gun then it might be a little difficult to achieve your goals. Oh and i recomend you get GGDT its a simulation software that shows you the velocity and mayn other useful things that your gun will have. Oh and if i where you i would try and either work on my spelling a little but more, proof read my posts and use the spell chack botton. After all i didnt know we where making candy here:
I'm getting ready to build a gum will be for all intensive purposes
:wink:


Yeah, I need to use my "spell chack botton", and this will be my 7th or 8th gun, and theoretically the 4" to 2" reducer is considered part of the barrel... What, I think, is making mine differant than a normal barrel sealing piston is that instead of a "solid" piston, the piston will consist of a 4"disc on one end and 24" away on the other end of a threaded rod is a 2" disc to seal the barrel, and Using ggdt(and a little theorizing)I calculated that by using this layout I can make the chamber shorter(because the barrel won't eat up volume) and keep the gases flowing in a straighter path( by not having to do a 180 to enter the barrel, and increase the velocity of the gases (by using the velocity stack to "squish" the gases into the barrel)...

the piston should workbetter than a normal barrel sealing piston because on a normal 4"x2" coax, with 100psi, there is 3.14"sq. being acted upon by 100 psi which = 314lbs of force holding the piston forward, and upon opening the pilot there is (12.56"sq minus 4.427"sq)=8.133" being acted upon by 100 psi which = 813.3 lbs of force pushing the piston backwards which= (813.3-314)=499.3 lbs of force acting to open the "valve"... Now with my layout, there is 314 lbs pushing forward, 1256lbs pushing backwards which =(1256-314)=942 lbs of force acting to open the "valve", which should decrease the time from closed to fully open greatly...

Am I still missing something??? :wink:

and BTW, I use a lot of "misspellings" to denote accent or emphasis, but sometimes I just get FAT fingers... LOL
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Unread postAuthor: sputnick » Tue Jan 27, 2009 6:23 pm

I'm sure he meant that the purposes are going to be INTENSIVE! like playing paintball with grizzly bears or something like that,

Ha ha I don't know, I didn't understand your description, just spent 2 hours writing an exam/essay about 4 books which I hated, so my brain is, for all intensive purposes, dead...

you should just have finished it then posted...
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Unread postAuthor: Hubb » Tue Jan 27, 2009 6:23 pm

I think I understand this, but a diagram would definitely help.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 27, 2009 6:29 pm

sputnick wrote:I'm sure he meant that the purposes are going to be INTENSIVE! like playing paintball with grizzly bears or something like that


The expression is incorrect, see.

Grammar fascism aside, is the piston arrangement you're planning something like this, only with the barrel in line with the chamber?

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Unread postAuthor: sputnick » Tue Jan 27, 2009 6:30 pm

I am aware that that is not a real word, I was poking fun, but thanks anyways jack...
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 27, 2009 6:35 pm

sputnick wrote:I am aware that that is not a real word, I was poking fun, but thanks anyways jack...


I know, I know, I'm in a mood ;)
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Unread postAuthor: clide » Tue Jan 27, 2009 6:41 pm

I believe the type of piston valve you are describing is commonly known around here as a "toolies" style piston valve. You should be able to search for "toolies" on the forum and come up with some good examples of this design being used.

As for the opening time, a toolies style piston will be nearly the same as a coaxial of equal dimensions maybe even <i>slightly*</i> slower because you don't have the momentum of the air working with you.

When calculating opening force you have to remember that the pilot pressure doesn't instantly decrease to zero.


*Not by any amount that would be noticeable in the final performance of the gun, and you still have better flow working for you in a toolies type.

Edit: Woops, didn't realize I took so long to hit the post button...
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 27, 2009 6:43 pm

clide wrote:I believe the type of piston valve you are describing is commonly known around here as a "toolies" style piston valve. You should be able to search for "toolies" on the forum and come up with some good examples of this design being used.


*cough*illustratedinmypostabove*cough*

:D
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Unread postAuthor: sputnick » Tue Jan 27, 2009 6:44 pm

Ah I see :D Well I am in a mood too, I am well on my way to building a modest little coaxial (my first!) with full wood stock and scope, its going to be a nice gun,

It should be done by the end of the week, seeing as I have the whole week off now that exams are done, the stock is the only piece that's really time consuming.
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Unread postAuthor: clide » Tue Jan 27, 2009 6:46 pm

jackssmirkingrevenge wrote:*cough*illustratedinmypostabove*cough*

:D


Yeah, yeah. I was doing two things at once and started the post before you posted that. Not my fault you are a posting machine :P
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Unread postAuthor: jeepkahn » Tue Jan 27, 2009 6:48 pm

Ok Ok...Intents and purposes.....

Ok here's a diagram...


edit: I guess it's a toolie then.... :roll:

second edit: Exactly what JSR said, the setup in his pic except inline...
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piston diagram.jpg
there will be a standoff near the barrel end to maintain alignment...
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Last edited by jeepkahn on Tue Jan 27, 2009 6:55 pm, edited 1 time in total.

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Unread postAuthor: jackssmirkingrevenge » Tue Jan 27, 2009 6:53 pm

Looking good, just make sure everything's aligned and you'll be fine :)
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