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Copper Coaxial Problems / Questions

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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Copper Coaxial Problems / Questions

Unread postAuthor: shadowzzz » Mon Aug 10, 2009 3:32 pm

I still have some unanswered questions about making a copper coaxial gun:


1. Is it a problem that the chamber is 22mm (3/4") and the barrel is 15mm(1/2")? Will a 12mm ( barrel ( smallest available copper here ) provide a better chamber to barrel ratio? Because it seems to me that using a 15mm barrel is like (22-15=7 ) using a 7mm chamber to fire a 15mm projectile... Thats kind of weird, isn't it ? Please tell me if this is a problem!

2. I am making a bolt piston in a 22mm T-housing and I will use a blowgun for piloting. Can I just drill a hole in an 22mm endcap, shove the blowgun in it, and hard solder it to the endcap and then solder the endcap with blowgun to the T ?

3. What pressure can a blowgun take if it takes pressure from the 'wrong' way? Because I am planning on letting it take pressure from the barrel ( if the blowgun would be an actual gun )


I have used the search function, but I didn't see solutions for these problems, please help me !

Quick Question: How does one keep the barrel suspended within the chamber in such a way that the suspension does not restrict flow and the barrel is neatly alligned with the chamber ? I would guess some iron wire braces, or are there better ideas?


(all the diameters are the Outer diameters of the pipe )
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Last edited by shadowzzz on Mon Aug 10, 2009 6:20 pm, edited 1 time in total.

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Unread postAuthor: jackssmirkingrevenge » Mon Aug 10, 2009 3:43 pm

1. Is it a problem that the chamber is 22mm (3/4") and the barrel is 15mm(1/2")? Will a 12mm ( barrel ( smallest available copper here ) provide a better chamber to barrel ratio? Because it seems to me that using a 15mm barrel is like (22-15=7 ) using a 7mm chamber to fire a 15mm projectile... Thats kind of weird, isn't it ? Please tell me if this is a problem!


Calculate the area, not the diameter - because this is the relevant dimension - and you'll look at it differently

3. What pressure can a blowgun take if it takes pressure from the 'wrong' way? Because I am planning on letting it take pressure from the barrel ( if the blowgun would be an actual gun )


It depends on the individual model, see if you can connect it to a pump the way you want to mount it and see at what pressure it leaks.
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Unread postAuthor: shadowzzz » Mon Aug 10, 2009 6:37 pm

Ahh ofcourse, area. How could I have been that stupid...
But does anyone has some idea's to mount a blowgun to a piston valve without quick connects and hoses and the like? Is soldering it reasonable?
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Unread postAuthor: skyjive » Mon Aug 10, 2009 7:04 pm

http://www.mcmaster.com/#catalog/115/455/=34tee7

Part number 6852K11 about 1/3 way down the page is a big blowgun with 1/4" thread ports at BOTH ends, so its easy to attach to other stuff in either direction
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Unread postAuthor: jackssmirkingrevenge » Mon Aug 10, 2009 8:57 pm

shadowzzz wrote:But does anyone has some idea's to mount a blowgun to a piston valve without quick connects and hoses and the like? Is soldering it reasonable?


Not as reasonable as good epoxy ;)
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Unread postAuthor: c11man » Mon Aug 10, 2009 9:04 pm

and any blowgun can have stuff mounted on either side, you just cant put pressure on the outlet of all blowguns
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Unread postAuthor: quincy18 » Tue Aug 11, 2009 6:08 pm

Anyone got the answer to this question :

Quick Question: How does one keep the barrel suspended within the chamber in such a way that the suspension does not restrict flow and the barrel is neatly alligned with the chamber ? I would guess some iron wire braces, or are there better ideas?

I also need to know that, also how big may the gap between the t-piece and the piston be for piloting ?

1 last question : How far must the piston travel for optimal performance ?

Xyro
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Unread postAuthor: Technician1002 » Tue Aug 11, 2009 7:09 pm

quincy18 wrote:Anyone got the answer to this question :

Quick Question: How does one keep the barrel suspended within the chamber in such a way that the suspension does not restrict flow and the barrel is neatly alligned with the chamber ? I would guess some iron wire braces, or are there better ideas?

I also need to know that, also how big may the gap between the t-piece and the piston be for piloting ?

1 last question : How far must the piston travel for optimal performance ?

Xyro


For me in the mouse musket, I simply took some poly tubing and cut pieces an inch or so long and zip tied them to the barrel about 6 inches from the breech. They compressed slightly going into the chamber on the Mouse Musket and worked fine. Maybe you need a hint of the size of the gap between the barrel OD and the chamber ID. The Mouse Musket is a coaxial with a 1 inch PVC barrel inside a 2 inch PVC barrel.

In terms of flow, since the air expands as the pressure drops the highest velocity is near the piston. The other end of the chamber doesn't see much flow. I position the support somewhat away from the piston to reduce friction loss and turbulence in the high flow area. The support does not have to be right at the breech to be effective.

Piston travel should be limited to between 1/4 and 1/2 the diameter. Minimum for flow is 1/4 diameter. I allow longer travel in mine for a higher coef. Part of the travel is into the bumper where it decelerates instead of hammering itself to bits.

I'm not quite sure of the gap and t piece you refer to, so I can't answer that question.
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Mouse Musket valve seat. Barrel is suspended by 3 pieces of poly tubing zip tied to the barrel about 6 inches from the breech.
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