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Piston and boltaction diagram

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: Hotwired » Mon Jun 01, 2009 9:49 pm

mark.f wrote:it's not significantly different from a normal piston valve.


I thought it was something different but now that you've labelled it up it IS a normal barrel sealer.

Instead of chamber filling by seepage round the piston when it seals against the barrel, you've sealed off the piston with o-rings and added a check valve. One step backward to go one step forward?

The usual rubber sealing face is replaced by a third o-ring which will be hanging on for dear life at 800psi when the valve fires.


?
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Unread postAuthor: Technician1002 » Tue Jun 02, 2009 12:50 am

Just a quick note. For a fast valve, make the valve seat at least 3/4 the diameter of the OD of the piston. The larger the seat is in relation to the OD, the lower the pilot area pressure needs to be before the valve unseats. Low pressure in the pilot area provides less resistance and pressure build up as the piston compresses the air in the pilot area.

A 2:1 diameter ratio (1/2 inch piston, 1/4 inch seat for example) has an area ratio of 4:1. (Pilot area on the piston is 4X the surface area of the front portion inside the valve seat) The piston will unseat at 3/4 the chamber pressure. If the pilot can't keep up venting, the piston when poped open could see pilot pressure reach 1.5 times chamber pressure with it only 1/2 the way open. As the chamber vents, the trapped pilot pressure will prevent a full opening.
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Unread postAuthor: john bunsenburner » Tue Jun 02, 2009 9:06 am

Well I would like to have this be a pneumatic QDV more than a piston valve. Thanks for the detail Gippeto, helped out and it was mor eor less what I was planning to do any how. One question however: does the starter drill's hole go all the way through the stock or is it just a dot int he middle. And for drilling do I just attach things to the 3jaw chuck or do I also use the tail stock and do I then drill from inside the 3jaw(you know how it has a hole that goes from the 3jaw to the end of the lathe...)?

Also thanks for that tech, i will make according dimensions.

@hot: this is work in progress, right now we are bouncing ideas back and forth, so we will go steps in all directions, stop us if we start entering more than just the x,y and z axes and go of nto other dimensions(arg geek joke!).
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Unread postAuthor: Technician1002 » Tue Jun 02, 2009 9:27 am

john bunsenburner wrote:One question however: does the starter drill's hole go all the way through the stock or is it just a dot int he middle. And for drilling do I just attach things to the 3jaw chuck or do I also use the tail stock and do I then drill from inside the 3jaw(you know how it has a hole that goes from the 3jaw to the end of the lathe...)?

Also thanks for that tech, i will make according dimensions.


Wikipedia has a great article on starter bits and drill bits in general.
http://en.wikipedia.org/wiki/Drill_bit

The starter bit is usually placed in the tailstock. Often a tailstock has a toolset that includes a centering point to keep long stock from wobble and a jacobs chuck to hold various drill bits, reamers, taps, dies, and other items that would not mount on the carriage.

The starter bit is not used to drill a hole through something, but just create a centered dimple to guide a drill bit so it doesn't wander when starting. Use this anytime you need a hole perfectly centered in a round piece. Drill bits being long and with the grooves, flat and twisted, they tend to be flexible, so they tend to wander when starting holes. The starting bit is round and short, so they can't wobble and wander when starting a hole.
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Unread postAuthor: spot » Tue Jun 02, 2009 2:35 pm

I made an adaptation to the design. Now it is mechanically opened, hopefully allowing it to open faster. I know its fairly (understatement...) complex but it should be do-able with a lathe.

If you don't understand the design, please take a look at nelson based paintball guns. I lend the trigger mech of it. (http://www.zdspb.com/tech/misc/anim_hammer.html) and of the insides of a bolt for a spring airsoft sniper. (I lend the bolt and spring guide and retention pin from it)

When you are not familiar with these designs, it will probably be HARD to underdtand the diagram.

Explanation of the workings: (In the diagram the bolt is cocked)
When the trigger is depressed, it pushes on the sear and so the hammer releases and moves back. There it hits the "bolt" (yellow) and actuates the QDV. Now it's time to recock the weapon. There is one part missing to do this (:p) so I will be uploading the better version in 10 minutes.
EDIT: make that tomorrow... Just noticed I have a ton of work left to do for school. School starts in 8 hours. Still have to sleep :S
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First draft version, I will update it some more to make it more clear.
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Last edited by spot on Tue Jun 02, 2009 5:11 pm, edited 1 time in total.

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Unread postAuthor: Hotwired » Tue Jun 02, 2009 3:50 pm

I have an almost identical series of diagrams and notes for that exact method from two weeks ago :wink:

I did make it even more complicated than that to make it semi automatic, but it's the same principles.


Nothing is complicated enough to be a unique thought in this place :shock:
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Unread postAuthor: john bunsenburner » Tue Jun 02, 2009 4:26 pm

Hot, you'v been commenting through out this whole thred saying that was my idea, omg!

Now get down to the the drawing bord and come up with somehtign new, and if i like it alot and it is the best design ill use it and engrave ur name into my gun....
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Unread postAuthor: Hotwired » Tue Jun 02, 2009 6:38 pm

No, I mean Spot's proposal.

It's identical in principle to the design I imagined a while ago. It's what I thought you were doing when you made this thread.

You use the QDV piston with the o-ring seals to close off the chamber then use a spring loaded weight to whack it backwards instead of manually tugging it.

No pilot gas (no need for a valve as the trigger) just a trigger that latches onto the sprung hammer then lets it go.


You fill from the chamber after cocking the piston and spring to seal it.


Here's one of my 2nd page diagrams about the valve system (second gen. paper cannon design):

Image

The hammer weight was dispensed with and it's a FIXED sprung piston which can now be cocked properly.

ONE port and full bore barrel, multiple ports and a sub bore barrel can be used but I had my reasons ^^
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Unread postAuthor: john bunsenburner » Thu Jun 04, 2009 4:15 pm

Thanks for all the help, one question i do have, still:

How long do i have to make the tube in which the barrel slided for the boltaction mech to have it accurate but not never-endlingly long...?

Really i can't go over 25 and the shorter the better.
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Unread postAuthor: spot » Fri Jun 05, 2009 9:39 am

The accuracy won't depend on how long the bolt slides over the barrel. (Unless you aim using the bolt, but that would be weird). Accuracy is more affected by the fit of the projectile, length of the barrel (So you can sight it better) and straightness of the barrel. It doesn't really matter much how long the bolt slides over the barrel, as long as it makes a good seal. Just choose what looks right to you ;)
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Unread postAuthor: john bunsenburner » Fri Jun 05, 2009 3:54 pm

Of coarse it matters: if the barrel isn't supported eanoth by the mechanism it will hand down, seeing as how i wan tto aim at tagets 500 or so yards away(AND HIT) it needs to be as accurate as possible, so no flopping barrel. Any more opinions, maybe some figures and formulas for back up? Rag, star, jsr, larda, jimmy and all the rest i am waiting for a long winded post that is summerized by the last few words:D!
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Unread postAuthor: spot » Fri Jun 05, 2009 4:02 pm

Let me get something clear: Are you going to pull the bolt backwards, or push the barrel forwards? IMHO in any case, the barrel should be supported by the stock (Or slide mechanism if you push the barrel forward, but if you are a accuracy nazi, that will cost you a little accuracy. But it won't be noticeable ;) ). And not by the bolt. The bolt's only function is the valve, it shouldn't have a supporting function. Having such a large piece of barrel in your bolt gives you an excessive bolt travel too. That will decrease your ability to put many bullets on target quickly since you will have to regain posure, and re-aim after each shot. With a small, light bolt travel you can just keep watching through your sights, and fire a round without having to re-aim alot.
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Unread postAuthor: john bunsenburner » Sat Jun 06, 2009 12:56 pm

Ok the bolt will be connected to the barrel. It works like any good old bolt action so this can't be that hard. How long do i have to make the tube around the barrel, the barrel support, or what every you want to cal it it have a stable barrel that doesn't wobble. there has to be a number, a formula, anything. Does anyone know?!
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Unread postAuthor: spot » Sat Jun 06, 2009 1:44 pm

Just look at a real bolt-action gun. Support the barrel along the whole length of the stock. Your barrel will be out of copper / another metal so it will not wobble if the end isn't supported...
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Unread postAuthor: john bunsenburner » Sat Jun 06, 2009 4:30 pm

well that is in a perfect world with perfect fitting barrels and diameters...
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