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making epoxy pistons

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Unread postAuthor: Counterstriker » Sat Mar 15, 2008 3:31 pm

jackssmirkingrevenge wrote:How thick is "the thick stuff"? It doesn't have to be like water, just runny enough to flow. As long as it's not a paste it should be adequate.


Well.. its like..a little thicker than hand soap. I will just have trouble pouring it in the 8 inch long 1/2" galvanized pipe without getting it all over the sides... Cause I can't cut another one in halve to cast it.. I think... Maybe they'll cut it for me.
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Unread postAuthor: Counterstriker » Sun Mar 16, 2008 3:03 pm

I Just bought a 3/4" 1 inch long nipple to cast it in..Is WD-40 any good for the lube? I am gonna go in the garage to see If I have any motor oil..
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Unread postAuthor: bigbob12345 » Sun Mar 16, 2008 3:10 pm

Wd40 actually works really well.
once it is cured just tap it out with a hammer a some blunt rod
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Unread postAuthor: SPG » Sun Mar 16, 2008 3:44 pm

And JSR how do we feel about "Gun Gum", which I believe is an epoxy based paste used for blocking small holes in exhausts or manifolds?

Only thinking of it because of course it's heat-resistant up to who knows what temp.
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Unread postAuthor: Counterstriker » Sun Mar 16, 2008 3:48 pm

SPG wrote:And JSR how do we feel about "Gun Gum", which I believe is an epoxy based paste used for blocking small holes in exhausts or manifolds?

Only thinking of it because of course it's heat-resistant up to who knows what temp.


I am gonna guess he will say something like this..

Low viscosity epoxy is neccesary for easy casting, You can cast with it but it will be pretty hard.

And this is the video of the some of the stuff I bought.

[youtube]http://www.youtube.com/watch?v=0BERECVVqrs[/youtube]


Also, I made a vid of me casting the epoxy for the piston.. Here :)

[youtube]http://www.youtube.com/watch?v=H9bQIe6JE5A[/youtube]
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Unread postAuthor: Counterstriker » Mon Mar 17, 2008 6:24 pm

*Update tro original post* I just was at a craft store and got http://www.utrechtart.com/images/products/82045.jpg
So I am good!
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Unread postAuthor: Velocity » Sat Apr 19, 2008 10:11 pm

Just tapped my piston out of the mold, and it looks great. However, I did this after 2 hours rather than 24 hours, and it feels a bit soft to the touch (not like hard plastic). Will it harden in the next 22 hours? I am kind of a noob with epoxy :lol: ...I hope I didn't screw it up by tapping it out early, but I was too excited 8)
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 20, 2008 3:36 am

Velocity wrote:Just tapped my piston out of the mold, and it looks great. However, I did this after 2 hours rather than 24 hours, and it feels a bit soft to the touch (not like hard plastic).


I would recommend popping it back into the mould and giving it a few more hours, in the sun if possible to quicken the hardening process :)
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Unread postAuthor: the beast » Mon May 19, 2008 6:16 pm

I know your not really supposed to revive posts unless its a good reason but it is. I was just wondering how you prevent the epoxy from fitting between the crack of the pvc innerwall and the rubber seal face. is it the grease? Or is the rubber face simply sealing it just enough?
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Unread postAuthor: FordGtMan » Mon May 19, 2008 6:54 pm

I found that it is easier to take some Styrofoam from an egg carton and seal off the tube that way, then tap the piston out and super glue the sealing face to the piston afterward. It is then easier to seal it off, but it may need sanding to make it strait because it probably wont be perfectly strait. JSR's epoxy casting tutorial shows this technique.
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 15, 2009 5:33 am

Here's the latest piston I cast for a 3/4" high pressure pneumatic I'm making, inside the copper pipe I'm using as a chamber.

I got a bit creative with the filling, I popped a few airsoft BBs in. It didn't do much for the the weight as they sank in the epoxy so are more dense, maybe 0.12 grams next time ;)
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Attachments
DSCF4419.JPG
freshly popped out of the mould, needs some finishing
DSCF4421.JPG
smoothed down and ready to be sealed inside
DSCF4421.JPG (39.97 KiB) Viewed 1784 times
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Unread postAuthor: inonickname » Sun Nov 15, 2009 5:48 am

Cool..

Though I'll admit I was worried for a second that you were considering using PVC in it..good to see you're using something which can take it.

Will it be serviceable?
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 15, 2009 6:10 am

inonickname wrote:Though I'll admit I was worried for a second that you were considering using PVC in it..good to see you're using something which can take it.


After a certain amount of prototypes blow up one you, one does tend to become a bit careful :P The barrel is PVC but it's 3.5mm wall thickness so no worries there.

Will it be serviceable?


The piston won't be removable, but the pilot will be a 1/2" ball valve and I'll cast it around the thread so that will come off with some effort without destroying it.
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Unread postAuthor: Technician1002 » Sun Nov 15, 2009 6:18 am

I would highly recommend a servicable valve. Gunk gets in and the grease blows out. I've had dried apple juice stick pistons, bits of grass wrapped around o rings, thread, bits of foam, etc. Disassembly for clean and lube is a normal part of air cannon maintenance. This was so important to me the most recently completed cannon is fully servicable by hand with no tools. My video on the Marshmallow Cannon shows how quickly the valve comes apart using no tools. It is only assembled hand tight for quick and easy service. A tube of lube and paper towels finish my field service kit.
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 15, 2009 6:34 am

Of course ideally it would be servicable, but such is my manner of construction. I do though make my pistons in such a way that (provided they are made well in the first place) they don't really need maintenance, no lube is required and the only seal is the sealing face which is 1/4" thick so it is unlikely to wear out for the duration of the launcher's usefull life.
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