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Whats the deal with O-rings and wood?

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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Unread postAuthor: LikimysCrotchus5 » Sun Sep 07, 2008 7:16 pm

I used lithium grease, but do you guys think i should try a rubber rod?

What material should it be made of?

8695K861

From mcmaster.

or 96405K72 which is a rubber ball that is 1 inch
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Unread postAuthor: Gippeto » Sun Sep 07, 2008 10:17 pm

The wood and epoxy pistons should have worked.

As mentioned, the hot glue piston, being so soft, will conform to imperfections on the end of your barrel, not so the other materials.

It seems reasonable to conclude that the end of your barrel is either not "square" to the piston bore, or has other imperfections.

Make a "sanding piston" from some of your 1" dowel. Using peel and stick sand paper, attach and trim a piece to the end of your dowel.

Use the piston bore as a guide, and sand the end of your barrel with this tool.

A sharpie pen rubbed on the end of the barrel, will show the low areas once you start sanding.

Sand until there are no more low areas, and then try one of your wood pistons again.

Hope this helps. :)
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Unread postAuthor: ALIHISGREAT » Mon Sep 08, 2008 1:38 am

i don't think rubber would work very well unless in was lubed very well.... but it may work, for my coaxial's piston i just got some HDPE rod the same as the ID of my chamber, and then just added a sealing face, it was ridiculously easy....
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Unread postAuthor: BlackH » Mon Sep 08, 2008 3:30 am

I had the same prob then i saw my barrel weren’t flush in the middle of my chamber so i made a spacer to keep it in the middle with pvc cut-offs and in my copper gun the barrel weren’t totally flat and made the air pass through. I also had a piston that did not want to move forward so in my coax I closed the "trigger valve" add some pressure and then open it to make the piston go forward and continued to add pressure then until i got the pressure i want

and o ps i have no lube in my piston used a little Q40 to get it in then i noticed once its dry and left it just once or twice sprayed some q 40 down the barrel and forced it down with an air sight object to clean out the barrel
and mine leaked through the screw and thread and if i tightened it, it made the sealing face bend to i e-poxyed a washer to the back of sealing face and after that i used the one and only piston and it never had to be serviced (touch wood)
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Unread postAuthor: jrrdw » Mon Sep 08, 2008 5:05 am

Air leaking through wood? What kind of wood are you using? Balsa? I used oak, my barrel leak came from the through bolt. I sealed that with JB Weld smeared all over the center bolt, reinstalled it, let it dry, no more barrel leak.

My wooden piston has a steel backing washer inbetween the piston and 1/8th thick rubber sealing washer, then another steel washer on top the rubber sealing washer slightly smaller the the barrel inside diameter leaving only a slightly larger sealing face then the wall thickness of my barrel.

Do you have your valve built into a tee? Is the sealing face on the barrel centered in the tee? Is your piston to short and tipping and jamming? Did you drill your EQ hole inside the barrel diameter by accident? Where your o-rings to tight? A spring is helpfull in sealing the piston to the barrel, as long as it's ajusted right.
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Unread postAuthor: LikimysCrotchus5 » Mon Sep 08, 2008 1:57 pm

It seems that i might have found my problem and im going to take all of what you all said into consideration when making my next piston.

If all else fails, ill just see what the rubber can do for me.
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Unread postAuthor: man_o_brass » Mon Sep 08, 2008 2:34 pm

I wouldn't try a rubber rod unless you find some really hard stuff. When pressure is put on the flat faces, it's going to expand radially like a compression fitting (i.e. a boat drain stopper) and wedge itself in place. Might cause a problem when it tries to open.
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Unread postAuthor: iknowmy3tables » Mon Sep 08, 2008 3:59 pm

I don't understand why is this thread so long I though the answer was clear, the air is leaking because the equalization hole is too big, and/or the o-rings aren't properly seated in a properly cut groove
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Unread postAuthor: LikimysCrotchus5 » Mon Sep 08, 2008 4:12 pm

Well it got beyond the title and i am just discussing piston materials as well, and what is most suitable.

Also those two things i did fix and it still leaked (i probably didnt make good groves but idk, ill just make one without)
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Unread postAuthor: LikimysCrotchus5 » Mon Sep 15, 2008 3:30 pm

Excuse me for posting twice in a row, but i am just giving you (all) a update on what i have been doing with this piston dilemma.

I have tried wood, yet again, and it worked, for a few tries. The sealing face pops and i can see why thats happening so i tightened the bolt and it stopped, only for a little time. Then i see that the rubber washer that i am using to put pressure under the sealing face is popping into the barrel but is not coming off the piston.

So i can fix this by putting on a new sealing face along with gluing the 3 pieces of rubber and putting on a better washer.

But... today, i came across a 6 inch, by 1 inch in diameter aluminum rod, which is great! What i have considered now is using that as a piston material because it so happens to be that my housing is 1 inch in ID. So i made sure it fit by placing it in there and it does.

Now i gave this some thought, the differences between using wood and aluminum as a piston and they are:

Wood;
1. Light weight
2. Can be problematic

Aluminum;
1. obviously on the heavier side but its stronger than wood so it has better impact resistance.
2. It maybe less problematic.

So this is what i have come up with so far but i know that there is more to be thought of.

I think i am going to try the aluminum and i will cut it down to par, and epoxy a sealing face on there and i think i will have a long lasting, somewhat light weight (compared to other metals) piston.

Comments and criticism is accepted.
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Unread postAuthor: ALIHISGREAT » Mon Sep 15, 2008 4:26 pm

i would just chuck the aluminium in because there will be no leak around the bolt as long as you do it up tightly.
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Unread postAuthor: Velocity » Mon Sep 15, 2008 6:08 pm

Just a question, how are you guys putting o-rings on your pistons? I don't think you are using lathes...I have tried to make latheless o-rings before, but I failed :oops:
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Unread postAuthor: LikimysCrotchus5 » Mon Sep 15, 2008 6:49 pm

Velocity wrote:Just a question, how are you guys putting o-rings on your pistons? I don't think you are using lathes...I have tried to make latheless o-rings before, but I failed :oops:


Right you are, i am the common poor spudder (middle class i would rather say) and i dont have a lathe, but i have access to one at school, but i dont take any woods or metals classes, but if i got off my ass and went to the teacher to ask if i could use one, then sure i would be able to.
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Unread postAuthor: LikimysCrotchus5 » Wed Sep 24, 2008 9:25 pm

Double post but ignore;

Now on to the good news:

I didnt get the aluminum to work because i jb welded the sealing face together and it made them hard, so i was just like screw it.

So i got a a wooden dowel from Ace hardware, and drilled a hole (not in the exact center, but o well) and i put a sealing face on it. After having problems with the rubber washer popping, so i got some small copper washers and they have yet to fail me.

Since i didnt have a bumper, the wood would (homophones) get stuck in the threaded bushing and this was destroying the wood. So i finally got a bumper that is a piece of tennis ball and it works great; the filling and the piloting is superb.

So to sum it up, its completely functional with no problems (except for the fact that if the piston was turned, it would not work because it wont seal right but i dont think that will become a problem and its a simple fix anyway)

So now all i gotta do is get the pump made and i got high pressures.

Yessss! :o (Napoleon Dynamite moment)
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Unread postAuthor: Gippeto » Wed Sep 24, 2008 11:40 pm

Good on ya! :D

I'm glad you stuck with it and got it working.

Never say die! :lol:
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