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Looking for Materials for a Compact Coaxial Design

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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Looking for Materials for a Compact Coaxial Design

Unread postAuthor: Xamllew » Sun Aug 21, 2016 11:19 pm

Hello everyone, new to airgun construction. I'm looking to start work on a .45 cal coaxial piston airgun. What I would like to know is where I can find certain parts for the air chamber, i'm looking for a 1/2" (13mm) steel pipe with internal threads on both ends and plugs that will fit those threads. I know I can find externally threaded pipes with caps for them but i really dislike the look of those. I'm looking to build what is basically an oversized pen-gun, or in other words I want the entire mechanism to fit inside of the pipe with only the valve protruding from the back, i will later build a stock around this build. any suggestions would be appreciated.
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Re: Looking for Materials for a Compact Coaxial Design

Unread postAuthor: jackssmirkingrevenge » Sun Aug 28, 2016 9:33 am

Have you considered Epoxy Casting as a construction method if you do not wish to be limited by standard fittings?
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Re: Looking for Materials for a Compact Coaxial Design

Unread postAuthor: Xamllew » Sun Aug 28, 2016 3:36 pm

jackssmirkingrevenge wrote:Have you considered Epoxy Casting as a construction method if you do not wish to be limited by standard fittings?


Yes I have actually considered epoxy. However I need at least one side of the air chamber to have a threaded end cap so that the gun can be taken apart and serviced if necessary.

Thanks for your response.
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Re: Looking for Materials for a Compact Coaxial Design

Unread postAuthor: jackssmirkingrevenge » Tue Aug 30, 2016 10:14 am

You can also epoxy a threaded fitting inside a tube, I had done this with several hybrid launchers
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Re: Looking for Materials for a Compact Coaxial Design

Unread postAuthor: Xamllew » Tue Aug 30, 2016 4:20 pm

jackssmirkingrevenge wrote:You can also epoxy a threaded fitting inside a tube, I had done this with several hybrid launchers


Ooh, I didn't think of that, that would be perfect. I wonder how difficult it would be to cast a female threaded epoxy adapter to fit permanently the breech and then have another epoxy casting to thread into that piece.

Another idea I had was to make an epoxy plug which seals the breach then drill a small hole through the breech wall and through the epoxy so that it can be pinned in place.
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Re: Looking for Materials for a Compact Coaxial Design

Unread postAuthor: Gippeto » Tue Aug 30, 2016 10:15 pm

Better plumbing supply shops will have flush bushings intended to be used with drawn copper....more reliable (JMO :wink: ) than epoxy.

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Material choice should largely be driven by expected stresses...what pressure are you thinking to use?
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Re: Looking for Materials for a Compact Coaxial Design

Unread postAuthor: Xamllew » Wed Aug 31, 2016 2:35 am

@Gippeto, Thanks for making me aware of that fitting, that might just me what I need, although with that bushing in, the piston diameter will have to be equal to the ID of the bushing for it to be removable, hmm.

As for psi, I will be using a shock pump, so 400 max.
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Re: Looking for Materials for a Compact Coaxial Design

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Re: Looking for Materials for a Compact Coaxial Design

Unread postAuthor: jackssmirkingrevenge » Wed Aug 31, 2016 9:30 am

Gippeto wrote:...more reliable (JMO :wink: ) than epoxy.


Having had my fair share of close shaves I'm not about to argue with that, however virtually all failures I've had with epoxy have been the result of over-optimistic design and under-engineered setups, if done right it will be as safe as any commercial fitting. That being said, if one has the resources for "proper" parts they should be the preferred option.
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