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Coaxial cannon help

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Coaxial cannon help

Unread postAuthor: Zach1188 » Thu Jul 16, 2009 3:24 pm

I am working on designs for a coaxial cannon, but I cannot figure out how to glue the barrel into the chamber (perhaps using a reducer) without smearing primer and concrete down the length of the barrel. Any ideas?

Also what alternatives are there for a chamber fan? It would be difficult to mount one in a coax.
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Unread postAuthor: Copperboy » Thu Jul 16, 2009 3:44 pm

Slide the barrel to about an inch from where you want it, then smear the lot where it needs to be and finally slide the barrel the last inch. (through the reducer)

Are you making a hybrid? If you're making a pneumatic then there's no need for a fan.

I've heard people sticking some debri of choice in the chamber and just shake it around for it to help mix the fuel.

Hope that helped!
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Unread postAuthor: Zach1188 » Thu Jul 16, 2009 4:08 pm

Ok thanks. I was under the impression you need to prime and concrete both joints before sliding them together. And its going to be a combustion cannon. I'm not too interested in pneumatics, and I don't have the know-how yet to make a hybrid.
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Unread postAuthor: Hotwired » Thu Jul 16, 2009 4:19 pm

You're concerned about smearing primer and cement on the barrel of a coaxial.


Now that's dedication to neatness.
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Unread postAuthor: Zach1188 » Thu Jul 16, 2009 5:04 pm

Hotwired wrote:You're concerned about smearing primer and cement on the barrel of a coaxial.


Now that's dedication to neatness.

I'll take that as a compliment :wink:
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Unread postAuthor: Copperboy » Fri Jul 17, 2009 2:32 am

Well, if you're making a combustion then there is really no need for pushing the barrel all the way into the chamber. (If we're thinking the same situation here :) )

Also, don't take my word for it to hold, I have absolutely no experience with PVC. But I think it's critical you smear primer etc. at both surfaces.

Switch to something a tad sturdier! :P
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Unread postAuthor: Zach1188 » Sat Jul 18, 2009 5:26 pm

We pressure rated PVC is usually plenty strong, I believe. I would go aluminum but I don't have the money or welding experience.

I guess when it comes time to build this thing I have no choice but to let the primer smear across the length of the barrel, inside the chamber. I assume I don't need to do the same with the PVC concrete, as it's just sandwiched between both pieces of primed PVC.
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Unread postAuthor: inonickname » Sat Jul 18, 2009 6:44 pm

Hotwired wrote:Now that's dedication to neatness.

And you're one to talk? :lol: :lol:

The barrel should really be supported plenty strong enough at the front of the chamber by a reducer or similar, all you need is a fairly tight fitting (make sure it has holes in it to allow gas flow of course) reducer or homemade bushing to support the barrel and prevent it wobbling around
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Neatness counts

Unread postAuthor: Technician1002 » Sat Jul 18, 2009 7:22 pm

Neatness counts. Here is my small launcher nested in the barrel of the larger launcher. The 1 inch barrel is primed with purple primer and glued. I respect neatness and attention to detail. Well done.
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Carefully glued barrel on the marshmallow cannon. No primer showing. Primer was applied to within 1/8th inch of the edge.
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Re: Neatness counts

Unread postAuthor: inonickname » Sat Jul 18, 2009 8:04 pm

Technician1002 wrote:Neatness counts. Here is my small launcher nested in the barrel of the larger launcher. The 1 inch barrel is primed with purple primer and glued. I respect neatness and attention to detail. Well done.


There's a difference between primer on the outside of the gun, where the world can see it and it being on the inside of the gun, where you might see it when you breech load..

But yes, neatness counts..
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Unread postAuthor: Copperboy » Mon Jul 20, 2009 7:36 am

I could see why you'd want a coax if you wanna refuel and load with just removing the endcap, but the same could be accomplished with just an union or similar. That would also give you plenty extra chamber volume.
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Unread postAuthor: frozebyte » Mon Jul 20, 2009 8:13 am

If you use metal (aluminium, copper, steel) you don't necessarily have to weld the barrel into the chamber, you could use epoxy like what most people do.

The barrel is placed into the chamber and prepared in the right way, before epoxy is poured in, and wait for the epoxy to cure.

Metals aren't that expensive anyway, couple of dollars could give you alot of pipe. Unless the situation there is different. There's a tutorial written by someone about using epoxy.... somewhere :D :D
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Unread postAuthor: Zach1188 » Mon Jul 20, 2009 3:29 pm

Aside from copper, pipe is fairly cheep here. Actually it's priced similarly to PVC if I'm not mistaken. I'm sure aluminum would be more than sufficient for my needs, so I don't think I need to go with steel. Unless there's something I'm not considering.

I did not even consider using epoxy, I have no idea why. That would be much easier than messing with primer/concrete. The only issue I will have with metal is a spark; I always have multiple spark gaps. I will just have to find a way to isolate the nodes. Is it safe to drill through the chamber of a metal spud gun? I know it weakens PVC and ABS. I'm sure it weakens anything to some extent, but with metal is it a significant danger?
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Unread postAuthor: Zach1188 » Sat Jul 25, 2009 11:39 pm

Sorry for the double post but I have another question.

How well would Gorilla Glue work for metal fittings? I have read around and it's said to adhere stronger than epoxy, however the glue itself is weaker. I was thinking of using it and then topping it off with epoxy, surrounding the gorilla glue.
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Unread postAuthor: frozebyte » Sun Jul 26, 2009 12:12 am

Not sure about gorilla glue, but epoxy will work just fine :)
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