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New JSR semi-auto prototype (split topic)

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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Unread postAuthor: JDP12 » Sat Jan 09, 2010 1:09 pm

hmm... psycix- would you ship to USA?
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Unread postAuthor: psycix » Sat Jan 09, 2010 2:53 pm

Sure. Shipping cost would be like 15 to 25 euro.
Hmm cheaper then I expected, and the shipping time to the US is shorter then to Poland! :lol:
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 09, 2010 2:59 pm

POLAND_SPUD wrote:what do you think about a design like this? the valve body could be machined in aluminium block while the 'spool' could be made from a threaded rod and machined disks with o-ring groves


Talk me through it, you put pressure in the pilot port, the spool moves up. contents of the spool vents through the barrel, shouldn't the "air source in port" be where the piloting port vents to reset the valve?

psychotische metaalbewerker wrote:So if you are interested, you could take some work out of the epoxy department and have it arrive in machined aluminum, steel, or Delrin.


If I have a worthwhile enough project, I might just take you up on that...

With such facilities at hand, I wonder why you aren't already churning out pneumatic cartridges :D

On that note, I've decided to ditch this prototype and give cartridges another go.
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Unread postAuthor: POLAND_SPUD » Sat Jan 09, 2010 11:28 pm

Talk me through it
the valve is operated just like a single acting air cylinder, that is - it's controlled with a NC 3 way valve
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Unread postAuthor: Skywalker » Sun Jan 10, 2010 12:33 pm

Ok, I got this idea from the assisted blowback that al-xg came up with here http://www.spudfiles.com/forums/14mm-automatic-air-rifle-t19321.html

here's my modification of it: use a slide valve to control the airflow, and incorporate that into the bolt.
Image

I forgot to include a trigger, which would be necessary; and the air flow comes in from the reservoir through the port in the bottom of the reciever.

What do you think? Workable?
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 10, 2010 12:45 pm

Skywalker wrote:What do you think? Workable?


Looks like it could work, given sufficient pressure, a tight fitting projectile and a fast enough valve. I would recommend a large face for the gas piston, substantially bigger than the calibre, to ensure reliable operation.
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Unread postAuthor: jackssmirkingrevenge » Mon Feb 08, 2010 3:17 pm

In my search for a light and effective valve for my upcoming sentry project, I've decided to give this configuration another go.

Instead of an all rubber piston, I put the rubber in a section of tight fitting aluminium tubing to eliminate any potential problems from the piston warping under high pressure.
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Unread postAuthor: JDP12 » Mon Feb 08, 2010 3:40 pm

hmm...

interesting. Eager to see the results of your efforts..
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Unread postAuthor: jackssmirkingrevenge » Mon Feb 08, 2010 3:58 pm

There's the usual 24 hour waiting period :roll: but true to form I'm not very optimistic hehe
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Unread postAuthor: JDP12 » Mon Feb 08, 2010 4:25 pm

I thought about throwing in a low joke about how eager i was but that I'd have to wait a whole bloody day...

But I decided that's been overplayed a fair bit so I omitted it from my post..

Then again, 24 hours is what I'm facing too with gluing together various prototypes and barrels...
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Unread postAuthor: jackssmirkingrevenge » Mon Feb 08, 2010 5:20 pm

Aye, the biggest drawback of adhesives really, apart from the mess. If only they could invent some way to make parts out of a block of hard material with some sort of machine tools instead of having to cast them :roll:
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Unread postAuthor: JDP12 » Mon Feb 08, 2010 5:32 pm

Yea... if only they could make those machines +CHEAPLY!!!

That's just asking for too much though...

Look for some updates of mine tomorrow CST for us yanks....

Gonna make up a prototype with a 3/4" bore
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Unread postAuthor: rikukiakuchiki777 » Fri Feb 12, 2010 2:05 am

What do you use as a piston material in your small-bores? How do you keep the sealing face bonded at high pressures? I remember being told that epoxy does not bond well to rubber...
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 12, 2010 2:22 am

Lately on my small bores I've been simply using solid rubber pistons cut from thich neoprene sheet with sharpened tubing as I did here.

In the case of the latest incarnation of this semi attempt (which didn't work by the bay, I misaligned the "barrel" - it's been bored out though so I'll repair it when I have time) the rubber sits inside aluminium tubing as in the diagram below so it bonds very well.

Another idea is to have a solid piston and have the rubber on your sealing face like on my mini-pistons.
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Unread postAuthor: CpTn_lAw » Fri Feb 12, 2010 3:29 am

This is what I did in the mini pen-gun I talked to you about a few months ago.
It worked , but the space between the aluminium of the piston and the copper of the chamber was too big, and much more air would come out the schrader than out the barrel. The idea was to use very thin adhesive tape, one half-layer aroun the piston, and weapons oil to smooth the action. This worked fine, but the small power it had made me forget it in a one of my toolboxes
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