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Basic full-auto pneumatic

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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Basic full-auto pneumatic

Unread postAuthor: skyjive » Wed Oct 22, 2008 8:46 pm

So I am attempting to build my first rapid fire gun and I think I have a pretty good design, except for one problem. I am planning to do a classic blow-forward bolt, which requires a section of pipe to fit closely inside another section and also requires o-ring seals. I don't have nada in the way of machine tools, so I can't lathe o-ring grooves or reduce pipe diameters or anything. What can I use as a bolt (fairly small caliber, I'm thinking 0.5"-1" barrel) and how can a seat o-rings without using machine tools?
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Unread postAuthor: Gippeto » Thu Oct 23, 2008 12:04 am

1) Epoxy castings. Cast with the o-rings in place, and then clean up the grooves later. Perhaps cast things around a suitable pipe?

2) Prayer? (might work best if combined with option 1) :wink:

Put up a paint or similar drawing, and you might actually get some help. :)
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Unread postAuthor: i-will » Thu Oct 23, 2008 12:39 am

in my opinion there isn't a simple full auto pneumatic or else we'd all have them. post a mock up of ur design so u can get some real feedback. and for the o-ring grooves i had a similar problem so i made my own tool for it. it's just some hinged scrap wood with a file taped to it. u put the pipe in the groove, squeeze just enough, then twist the pipe against the file by hand. when u finish u can smooth the groove with fine sand paper or do what i did. spray it with just enough clear coat spray paint. cant get any smoother than that. it worked for me.

<a href="http://s90.photobucket.com/albums/k273/PROGRESSKATE/?action=view&current=groover.jpg" target="_blank"><img src="http://i90.photobucket.com/albums/k273/PROGRESSKATE/groover.jpg" border="0" alt="Photobucket"></a>
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 23, 2008 1:00 am

You don't really need o-rings, just components that are a tight fit, and as mentioned above, epoxy casting is a good way to go about this ;)
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Re: Basic full-auto pneumatic

Unread postAuthor: Velocity » Thu Oct 23, 2008 1:16 am

skyjive wrote:So I am attempting to build my first rapid fire gun and I think I have a pretty good design, except for one problem. I am planning to do a classic blow-forward bolt, which requires a section of pipe to fit closely inside another section and also requires o-ring seals. I don't have nada in the way of machine tools, so I can't lathe o-ring grooves or reduce pipe diameters or anything. What can I use as a bolt (fairly small caliber, I'm thinking 0.5"-1" barrel) and how can a seat o-rings without using machine tools?


If you don't have nada in the way of machine tools, just pull out your lathe and cut some o-ring grooves...easy.

But back in reality world, yeah, you don't necessarily need o-ring grooves. I think they might be able to improve efficiency a bit, but really, they are not essential. I never really liked blow forward bolts, because it seems like a huge percentage of the performance is being sacrificed for fully automatic capabilities.

...though I am the same person who refuses to put a breech loader on a ten foot barrel for fear of efficiency loss...for god sakes, I don't even take the things above 50 PSI, I don't know why I bother :roll:
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Unread postAuthor: i-will » Thu Oct 23, 2008 1:36 am

jackssmirkingrevenge wrote:You don't really need o-rings, just components that are a tight fit, and as mentioned above, epoxy casting is a good way to go about this ;)



what ever u say. but i'm just giving him what he asked for and sharing an idea. take it or leave it.

gippeto also says that prayer is involved. doesn't sound very simple at all. also epoxy isn't always in the budget.

with the tool i made i only payed $2 for the file, $1 for the clear paint, and already had the o-rings from crap i took apart. i'd pick this over epoxy any day (unless i couldn't find the right size part to groove).

ur right though. no need for o-rings on a blow forward bolt.
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Unread postAuthor: CasinoVanart » Thu Oct 23, 2008 2:01 am

I don't have o'rings on my "Blow forward "Bolt"" :D
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Unread postAuthor: jimmy101 » Thu Oct 23, 2008 11:06 am

If you do decide to use O-rings it is pretty easy to cut the groove in soft metal (like copper) with a triangular file. Just mark a line around the piece and start filing. Take you time, and perhaps use a guide to keep the file square to the work piece.

You can smooth out the final groove by folding a piece of fine sand paper (perhaps 300 or 400 grit) around the file and doing a final wet sanding.

You could probably use a standard metal working file in place of the triangular file.

EDIT: engrish
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Unread postAuthor: skyjive » Thu Oct 23, 2008 12:57 pm

As always, thanks for the help guys. I'll probably try cast epoxy (was thinking that already but not sure if it was airtight enough) although the ghetto o-ring cutting tool looks pretty sweet too.
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Unread postAuthor: i-will » Thu Oct 23, 2008 1:39 pm

skyjive wrote: although the ghetto o-ring cutting tool looks pretty sweet too.


u'll find that everything i do is ghetto. that's how it is when faced with an insufficient income (i ain't got no money, dog). :lol:
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Unread postAuthor: FishBoy » Thu Oct 23, 2008 4:52 pm

CasinoVanart wrote:I don't have o'rings on my "Blow forward "Bolt"" :D


mind elaborating?
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Unread postAuthor: nivekatoz » Thu Oct 23, 2008 5:32 pm

I found that a 1/2" brass pipe nipple will fit just right inside a 3/4" brass pipe nipple.. Im not sure if this will help you. but there you go.
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 24, 2008 4:11 am

FishBoy wrote:
CasinoVanart wrote:I don't have o'rings on my "Blow forward "Bolt"" :D


mind elaborating?


You probably don't want to go there :roll: :D
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Unread postAuthor: dongfang » Sat Nov 01, 2008 5:13 pm

Hi,

If you have a dremel, check the router table for it. You can stick a cutter tool in the dremel, set the height so it sticks up just a few mm, and then turn the part over the cutter.

Cylinder side and end cuts are both possible. Side: Use a wheel cutter. End: Use a router cutter.

I have used this successfully some times.

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