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Sheet rubber for pistons?

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Sheet rubber for pistons?

Unread postAuthor: tony48 » Sat Mar 26, 2011 10:49 pm

I need to get some sheet rubber or similar material for my 3" barrel sealing piston and I can't find any sheet rubber. I've tried lowes but I'm not sure exactly where to look. Any help or suggestions?
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Unread postAuthor: mark.f » Sat Mar 26, 2011 10:55 pm

The plumbing section will have SBR gasketing (red sheeting) for things like toilets. Go for 1/8" thickness for a 3" piston.

1/4" or thicker can be ordered from places like McMaster in better materials (Buna-N, EDPM, etc.).
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Unread postAuthor: tony48 » Sat Mar 26, 2011 11:01 pm

Thank you very much for the quick response. I will check my local hardware store and Lowes
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Unread postAuthor: clemsonguy1125 » Sun Mar 27, 2011 12:28 pm

I get mine at Lowes. Its at the end of the toilet isle I think. Its labeled packaging rubber I think. It comes in 2 thicknesses. The people working there didnt know it existed though.
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Unread postAuthor: Technician1002 » Sun Mar 27, 2011 3:00 pm

I found the sheet neoprene sold by the pound at my local non big box hardware store. Find a store that has nails by the pound, instead of by the box or pail.

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Unread postAuthor: clemsonguy1125 » Sun Mar 27, 2011 3:08 pm

Depending on the size, Ive used rubber keychains or rubber washers.
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Unread postAuthor: mark.f » Sun Mar 27, 2011 5:16 pm

I dislike neoprene, actually. Used it on a few valves before I found the SBR stuff at Lowes. It doesn't seem to hold its shape as well as SBR and definitely not as well as nitrile, but I doubt it makes much difference. On my earlier valves I used high durometer sheeting from McMaster which seemed to work well.
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Unread postAuthor: LeMaudit » Sun Mar 27, 2011 7:47 pm

Maybe I'm going to say something stupid... :roll:

... but the last nice and shiny rubbery sheet I remember have seen in a store was one in the Art & Craft Store, made to carve rubber stamps out of it.

I can't remember really the hardness of it. Something like an eraser maybe. Now I'm thinking maybe it's too soft for a hard seal...

hmmm... I wonder if one could use polymer clay for that (the elastic kind). The hardness can be adjusted to anything from very hard to very soft. And the thickness is up to the user :wink:

Something to experiment :D
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Unread postAuthor: mark.f » Sun Mar 27, 2011 7:53 pm

I guess the next question would be if the composition was similar to an eraser? It's the addition of sulfur, I believe, which makes it crumble?
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Unread postAuthor: LeMaudit » Sun Mar 27, 2011 8:00 pm

I know people use erasers as a cheap rubber stamps. I guess the real thing must be tougher to resist compression and keep details crisp.

I don't know much those materials, but this page say some blank stamps are made of "vinyl".

http://www.stampeaz.com/index.php?main_page=product_info&products_id=1

No idea about the sulfur... is there a chemist in the room?
My school knowledge is... old :D
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Unread postAuthor: ramses » Sun Mar 27, 2011 8:37 pm

On a *slightly* related note, can anyone think of a good way to secure rubber to the curved part of a 3" PVC cap? Would leather work as a sealing face?

Thanks.
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Unread postAuthor: Gun Freak » Sun Mar 27, 2011 8:46 pm

I dont think leather would work as a sealing face. As for securing the sheet rubber, maybe try a bolt through the cap with a large metal washer behind the rubber?
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Unread postAuthor: clemsonguy1125 » Sun Mar 27, 2011 8:50 pm

What might work is a piece of theraband glued to a washer and bolted on.
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Unread postAuthor: ramses » Mon Mar 28, 2011 10:13 am

I would use a metal washer, except the front of the piston is actually curved.

Perhaps I should try some metal-spinning on my mini lathe?

I suggested leather only because it could be more easily attached than rubber, being somewhat porous.
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Unread postAuthor: Technician1002 » Mon Mar 28, 2011 12:16 pm

I used one of those dome 3 inch sched 40 pipe caps in my Dragon cannon. To solve my seal issue, I put the seal in the valve seat instead of on the domed piston.

The 2.5 inch barrel was shaved down some at the end to accommodate an o ring. A ring cut from a coupler completed the groove in the end of the breech of the barrel.

Stick on sand paper was used to shape the valve seat to the dome of the piston. The groove was filled with silicone rubber and a o ring was seated in the groove and held in place by the waxed piston until the silicone set.

The downfall of the domed piston was the valve slamming open busted the piston. It didn't last long. It is difficult to create an effective bumper for that shape.

The Mouse musket was built just before the Dragon. They share the same valve seat design.

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The dragon.. 6 inch chamber, 2.5 inch barrel coax. Used a 3 inch pipe cap for a piston.
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