help with pnematic pen gun

Miniature guns are novelty custom, unique, and sometime downright crude! Common construction materials often include pill bottles or pens. Show us your work!
EvilFish
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Wed Aug 05, 2009 1:08 am

hello, recently i have gotten into spudding, and mini's are my faveourite, even though i have a nice big one :twisted:
but right now i am trying to make a pen gun, and i want it to be small and easily carried around. so far i have an idea of using a copper tube from an old windchime as a barrel. it is 9cm long, and has a diametre of 6mm,
my chamber is 4cm of "1 Pvc Pipe. I have heard of many different valves on this site, but i think i should use either a ball valve (cheap and simple) or a Piston valve (better). could someone tell me where to get or make one of these for my cannon. thanks if you can. also i was thinking that, to make it mobile it would be useful to have a pump with it (attatched onto the side, pumping into the chamber directly). I cannot find any small pumps, but i have a lot of syringes, and was thinking that i could somehow make one into a pump? any help apreciated Thanks. :)
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jackssmirkingrevenge
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Wed Aug 05, 2009 3:56 am

For a small calibre (and especially with such a short barrel) if you want decent power you're going to need a small, high pressure chamber.

Have a look at this one for some building advice.

I would suggest you get yourself a shock pump, they are relatively cheap, compact and will easily help you reach high pressure.
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Mr.Sandman
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Wed Aug 05, 2009 11:11 am

Im confused, you said you wanted a pen gun correct? Then why is your chamber 1 inch pvc? Thats way bigger than a pen.And a ball valve? Thi isnt making sense to me. penguns are the diameter of a pen but maybe shorter or longer.
Yeah, it's that important.
EvilFish
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Wed Aug 05, 2009 6:47 pm

@Jsr: this doesnt need to be super high power,as its just going to be a plinker, for shootin' spitballs in glass etc. it would be nice to have a high power one, but im completely broke, and its hard making something good on a budget. also i have lookd into shock pumps, but as this only needs to got to 60 - 70 psi max, i dont think its worth the extra cash, which is why i want to make a syringe pump.
@ MrSandman: maybe its not a pengun, but i thought penguns were just small guns with pen tubes as a barrel? sorry iff i were wrong. :oops:
here is a diagram of how it works. and why is a ball valve making no sence to you? also, what valve should i use???

edit: I have now looked at your pengun Jsr, and was wondereing what its C:B ratio is? because mine will have a 1:1 ratio, and was wondering how powerful that would be at 60 - 70 psi? also, if i managed to make a mini pump (i also have some copper tube, so i could use that as well) and what sort of valve should i use for filling? or should i just have a tube from my pump leading direct into chamber. would that work???
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her is a diagram of how i want it too work.
her is a diagram of how i want it too work.
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jackssmirkingrevenge
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Thu Aug 06, 2009 2:12 am

EvilFish wrote:this doesnt need to be super high power,as its just going to be a plinker, for shootin' spitballs in glass etc. it would be nice to have a high power one, but im completely broke, and its hard making something good on a budget. also i have lookd into shock pumps, but as this only needs to got to 60 - 70 psi max, i dont think its worth the extra cash, which is why i want to make a syringe pump.
If you use a small diameter syringe (say a 1mL or 2mL one) attached to a schrader as a check valve, you should be able to reach some pretty high pressures (keeping a small chamber) but for the low pressures you want a 10 or 20mL will be ideal as it will take a lot less strokes.
MrSandman: maybe its not a pengun, but i thought penguns were just small guns with pen tubes as a barrel? sorry iff i were wrong. :oops:
here is a diagram of how it works. and why is a ball valve making no sence to you? also, what valve should i use???
The term "pen gun" usually refers to a gun made to look like a pen, something like this:

Image

This is my original project that "started the trend" on spudfiles :)
I have now looked at your pengun Jsr, and was wondereing what its C:B ratio is? because mine will have a 1:1 ratio, and was wondering how powerful that would be at 60 - 70 psi?


I think it's around 1:1, pretty powerful but that comes from the 400 or so psi I put into it :p still, depends on the valve you use. If you're using a ball valve a higher ratio (2:1 or so) should help with power.
also, if i managed to make a mini pump (i also have some copper tube, so i could use that as well) and what sort of valve should i use for filling? or should i just have a tube from my pump leading direct into chamber. would that work???
If you're having it permanenetly attached to the launcher, might as well fir a tube direct to the chamber, but you'll need to add some sort of check valve to stop the pressure coming back. A normal schrader is unsuitable for your purposes because it takes 70 psi just to crack it open.
EvilFish
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Thu Aug 06, 2009 2:23 am

how can i attach a syringe to a schrader valve, or make a check valve if i want to make it pump directly into the chamber? also, don't syringes suck air from the front nozzle (for sucking liquids into them) so wouldnt evrytime i pump, i'd be just taking air out of the chamber and putting it back in? would there be any way to modify it so it would fill from the back end? i was thinking that if you could show me how to make a check valve, i could simply poke some holes in the wall near the top, to let air in there. would that work?

may the FSM be with you.
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jackssmirkingrevenge
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Thu Aug 06, 2009 2:35 am

That's the point of a check valve, it allows flow in only one direction so you can push air into the chamber but not suck it out. You would need a hole in the other end of the chamber body to allow the syringe to re-fill with air, or remove the plunger completely after every stroke.

It really would be much, much simpler if you coughed up a couple of dollars for a shock pump, or even a normal pressure pump, they really aren't that expensive ;)
EvilFish
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Thu Aug 06, 2009 2:43 am

but i wanted it to be ghetto... :(
however, the main point is, where can i buy ( or better yet, how can i build) a decent, small check valve?

edit: also, what sort of valve could i use as a trigger? and where would i buy/make a valvefor it (6mm diameter barrel)
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Thu Aug 06, 2009 2:51 am

EvilFish wrote:however, the main point is, where can I buy ( or better yet, how can I build) a decent, small check valve?


This was my interpretation ;)

Image

You should find small check valves at any hardware store though.
what sort of valve could I use as a trigger? and where would I buy/make a valve for it (6mm diameter barrel)
Ideally you make a piston valve, as in my pen gun. If you want to go with a ball valve it's going to be bulkier and impossible to aim, unless you make it spring loaded which is complex and still not as effective as a piston valve.
EvilFish
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Thu Aug 06, 2009 2:59 am

but how to make a piston valve? i have looked at it, but have not found answers for building a very small piston valve. also, would I be able to build a small copper pump easily, and are there any how to's on this site? also is there a how to for the building of a check valve? i understand the whole principle, of what you have there, but it would be benifit to me if a how to was there. if i have to, i could probably figure it out myself, though. :)
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inonickname
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Thu Aug 06, 2009 3:33 am

Gippetto has a guide on building a track pump. Jack has already linked you to his pengun projects which obviously involve small pistons. Gippeto's guide also involves building a check valve.

You need to do the research.
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jackssmirkingrevenge
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Thu Aug 06, 2009 4:26 am

EvilFish wrote:If I have to, I could probably figure it out myself, though. :)
As was pointed out above, doing that and using a bit of ingenuity would prove your worth to other members of the forum, no one wants to be a spoonfed baby ;)
EvilFish
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Thu Aug 06, 2009 4:49 am

Hehe Lol so True....
have got a basic prototype working with syringe pump, crummy leaky check valve, homemade ball valve and ridiculous amounts of duct tape...
only goes to 35 psi...
am working on making a better working version (150 - 200psi) with a mini copper pump.

Thanks for all teh help JSR, and may the FSM bless you.

Edit: aslo does anyone think that i should post a small how to on the syringe pump? it itself can pump to 80 psi. not bad for something 3 cm long and made for 35 cents...
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inonickname
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Thu Aug 06, 2009 5:00 am

By the way, for anyone who wonders what the hell the FSM is..

Clicky.

You could do something with the pump, but it's a concept nearly everyone here would be very familiar with.
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FORE!!!!
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Thu Aug 06, 2009 6:51 am

inonickname is the a way u could translate the clicky link posted above about fsm , i mean wtf seriously i tryed reading that jargon and am still puzzled on as to what fsm (flying spaghetti monster ) is??
is there a chance of u dumbing it down a bit if u know what i mean.
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