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Piston on coaxial -- barrel not in center

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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Piston on coaxial -- barrel not in center

Unread postAuthor: psycix » Mon Oct 29, 2007 3:24 pm

Hey,

Im making plans these days now to build a coaxial pneumatic (will be my first pneumatic) and since I live in holland (europe) I dont have acces to the normal recuders you guys use to go from chamber size to barrel size.
Mine look different.
The point is, that the hole for the barrel is not in the center of the adapter. But more to the side.

Can this be a problem with a piston because of strong forces getting pushed on it, but now not being linear.

Was just wondering and wanted to know if its a problem.

Drawing:
--------------------------------------------CHAMBER WALL
| |---------------------------------------- <-BARREL WALL
| |---------------------------------------- <-BARREL WALL
| |
| |
| |<- piston
| |
--------------------------------------------CHAMBER WALL



EDIT:
I added a pic now!
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Unread postAuthor: ALIHISGREAT » Mon Oct 29, 2007 3:33 pm

if you can't get reducers, you could cut some wooden or plastic discs to center the barrel where you want it then you could epoxy the barrel in? would this work?
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Unread postAuthor: psycix » Mon Oct 29, 2007 3:49 pm

so i could build my own recuder/adapter out of sheet PVC?
Will that hold much pressure?
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Unread postAuthor: ALIHISGREAT » Mon Oct 29, 2007 4:39 pm

as i said, cut some discs and slide them a bit dow the barrel/chamber and fill the gap with epoxy...

_________________________chamber
_______________________l__barrel
_________________________barrel
_______________________l__chamber

so the verticle lines would be the discs and the gap between the discs and the end would be filled with epoxy, i don't know how much would be needed though, i think JSR is the resident epoxy expert :thumbleft: you could also put another pvc disc over the epoxy to make it look better.
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Unread postAuthor: MrCrowley » Mon Oct 29, 2007 7:36 pm

Do you mean you have an reducer like this?
Image

We have those here in NZ as well, just go to a plumbing merchant or something, they should stock proper ones.
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Unread postAuthor: spudgunnerwryyyyy » Mon Oct 29, 2007 8:31 pm

jsr said something like for 1.5" pipe 1/4" of epoxy is needed to get to 90 psi so i say a shiite load of epoxy sounds good to me.
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Unread postAuthor: nz_cannons » Mon Oct 29, 2007 8:56 pm

I remember making a homemade reducer fitting, it was a circle cut from a sheet of 15mm thick PVC. It was 50mm round with a 14mm hole in the center. I glued the barrel to the PVC using epoxy (barrel was aluminium) then used PVC cement to glue the piece to my main chamber.

Problem was that using something as thin as 15mm means there's not a lot of surface area for the glue to make contact with.
When pumping it up, it got to 90psi and the whole thing, barrel and all blew out of the chamber and hit a wall.

My advice if making something like this is aswell as throughly gluing it, is to put in 3 -5 self tapping screws to help make the join between the chamber and the reducer a lot stronger. Could also put a bit of glue on the screws aswell.
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Unread postAuthor: Pilgrimman » Mon Oct 29, 2007 9:58 pm

If you have to use the weird (well, to me anyway :) fittings, just put one on the back, and have it be the piston housing.

Line the small hole up with the end of the barrel. It's easy, and minimizes pilot volume! :D I'm looking at you, JSR!!!!
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Unread postAuthor: psycix » Tue Oct 30, 2007 10:48 am

Ive put on a picture of the 110mm->50mm reducer on my combustion.

Hope this clears things up.

At my country, almost all reducers are like that.
It has a 50mm female hole and is 110mm male itself
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 30, 2007 11:13 am

If the piston is not centrally supported, it will leak or at worst jam.

Maybe this can be helpful? I never used commercial reducers, always made my own.

It's easy, and minimizes pilot volume! Very Happy I'm looking at you, JSR!!!!


Efficiency, you know it makes sense :)
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Unread postAuthor: psycix » Tue Oct 30, 2007 11:31 am

jackssmirkingrevenge wrote:If the piston is not centrally supported, it will leak or at worst jam.

Maybe this can be helpful? I never used commercial reducers, always made my own.

It's easy, and minimizes pilot volume! Very Happy I'm looking at you, JSR!!!!


Efficiency, you know it makes sense :)


Hmmm that looks cool.... I consider it as an option....
Can some epoxy seal off a 80mm tube?
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 30, 2007 11:45 am

psycix wrote:Can some epoxy seal off a 80mm tube?


If you apply it thick enough (about 10mm) and use pour it over reinforcement like wire mesh or metal sheet, it will do so easily. A good example is the launcher I just linked you to:

edit: Another method I've used is to cut a disk out of plywood and fix it in place making sure the edges are sealed, then pour a layer of epoxy over it. The thicker the wood, the less epoxy you will have to use. Yet another way of reinforcing it would be to drill holes in the end of the pipe and insert bolts or nails, I've included a diagram showing an end view. I showed 4 bolts as a minimum but the more you add, the stronger it will be.

If using epoxy, be sure to check out my posts in the how-to section to ensure maximum strength.
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Unread postAuthor: psycix » Tue Oct 30, 2007 5:02 pm

Up to how many psi can such a thing hold?
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 30, 2007 5:42 pm

I've use it up to 150 psi with no problems at all.
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Unread postAuthor: psycix » Wed Oct 31, 2007 10:06 am

And what if i want to go 300 PSI?
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