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Epoxy Thickness

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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Epoxy Thickness

Unread postAuthor: clemsonguy1125 » Mon Jul 05, 2010 2:02 pm

On my new "stick gun"(a coax) the chambers 1" pvc and the barrels 1/2" cpvc. Since they are different pipe i will be using JSRs epoxy method to connect them, my questions how thick should the epoxy be.
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 05, 2010 2:05 pm

What pressure do you plan on running at?
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Unread postAuthor: clemsonguy1125 » Mon Jul 05, 2010 2:05 pm

100 psi
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 05, 2010 2:08 pm

Assuming that you're using good quality epoxy and properly roughen up the PVC, 1/4" thickness should be more than enough.
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Unread postAuthor: clemsonguy1125 » Mon Jul 05, 2010 2:54 pm

Im using Devcon 2 part epoxy that comes ina double syringe, its rated to 1500 psi
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 05, 2010 3:04 pm

this stuff?

I usually find that the quicker it takes to cure, epoxy tends to be relatively weaker, plus this stuff looks like it will be more of a paste thank a liquid meaning you might find it difficult to "pour" as a casting. Still, if you pile it on thick enough it should do.
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Unread postAuthor: MRR » Mon Jul 05, 2010 3:34 pm

@JSR
Since you are the authority on epoxy I'd like to ask you if you have experimented with filler / hardener ratios. Usually I use an epoxy that comes in a can and it's mixed 2:1. The first time I mixed it by eye and the result was a very good piston. The 2nd time I used syringes for the optimal ratio but that one became so hard and brittle that it crushed inside the cannon at the first shot.
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Unread postAuthor: clemsonguy1125 » Mon Jul 05, 2010 4:06 pm

That's it but it's a liquid, I already cast a piston from it around a rubber stopper and I'm about to pour it for the fitting thanks I'll use about a half inch so it wont leak thanks
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 05, 2010 10:59 pm

MRR wrote:Since you are the authority on epoxy I'd like to ask you if you have experimented with filler / hardener ratios. Usually I use an epoxy that comes in a can and it's mixed 2:1. The first time I mixed it by eye and the result was a very good piston. The 2nd time I used syringes for the optimal ratio but that one became so hard and brittle that it crushed inside the cannon at the first shot.


For pressure bearing components one should always use the correct ratio for maximum strength, however as you say not adding enough hardener will usually result in a less rigid component. I've never deliberately done this but have occasionally ended up with chamber caps that expand alarmingly when pressurised due to insufficient curing.

Had you used a good bumper?
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Unread postAuthor: MRR » Tue Jul 06, 2010 12:14 am

The piston had very small travel and I used two rubber washers @ 200psi. That shouldn't have happened in my opinion but maybe the epoxy that I use is simply not the right stuff for this application.
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 06, 2010 12:47 am

In general I find that epoxy is not useful for situations involving unbuffered impacts, changing hardener proportion will change the hardness and consequently level of tolerance to shattering however it's easy to go overboard and get something with the consistency of plasticine...
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