Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 51 users online :: 4 registered, 0 hidden and 47 guests


Most users ever online was 218 on Wed Dec 07, 2016 6:58 pm

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Thoughts/Suggestions on Rifle design

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.
Sponsored 
  • Author
    Message

Thoughts/Suggestions on Rifle design

Unread postAuthor: Alster370 » Sat Aug 20, 2011 8:09 am

Heres my design for an upcoming pneumatic rifle, I tried to keep things as simple as possible building wise whilst keeping high performance. It is a coaxial design with single shot chamber, shrader filling valve and a shrader for the trigger.

A pipe is sleaved over the trigger shrader, this pipe contains a small push rod that is connected to the firing lever. when the trigger is pulled towards the user, the rod pushes down on the shrader pin releasing air from the pilot volume allowing the piston to be pushed back by the chamber air allowing the gun to fire. Air that is released from the shrader exits though gaps in the mechanism, as well as holes drilled into the pipe covering the shrader valve.

The piston is a piece of steel pipe with a close fit to the ID of the chamber, which has a rubber sealant at the front, with epoxy filling the rest the space.

The piston backstop is a piece of steel pipe (same pipe as used with piston) which has a firm rubber epoxied onto the edge of the pipe. The pipe has thick 3mm walls so a good amount of surface area is there for the rubber backstop.

Hope you like it, suggestions/ thoughts appreciated. :D





Image

Image
  • 0

User avatar
Alster370
2nd Lieutenant
2nd Lieutenant
 
Posts: 243
Joined: Mon Feb 21, 2011 9:34 am
Reputation: 0

Unread postAuthor: Gun Freak » Sat Aug 20, 2011 8:37 am

A schrader pilot needs an o-ring piston at this diameter or a custom machined piston for tight tolerance. How tight is your piston?
  • 0

OG Anti-Hybrid
One man's trash is a true Spudder's treasure!
Golf Ball Cannon "Superna"M16 BBMGPengunHammer Valve Airsoft SniperHigh Pressure .22 Coax
Holy Shat!
User avatar
Gun Freak
Lieutenant General
Lieutenant General
 
Posts: 4969
Joined: Mon Jan 25, 2010 4:38 pm
Location: Florida
Country: United States (us)
Reputation: 11

Unread postAuthor: Alster370 » Sat Aug 20, 2011 9:40 am

depends, im still waiting on an email for the exact ID of 22mm pipe from my supplier. But hopefully 0.25mm gap max. But if its what I think it is then 0.01mm. If the pilot volume is kept to a minimum, will that require less tolerance on how tight the piston is because it can drain the pilot of air faster?

oh and the drawing isn't to scale, im using 22mm pipe. The drawing makes out that im using 28mm or more. Sorry about that.
  • 0

User avatar
Alster370
2nd Lieutenant
2nd Lieutenant
 
Posts: 243
Joined: Mon Feb 21, 2011 9:34 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sat Aug 20, 2011 9:54 am

Careful.

22mm pipe cross sectional area = 3.801 cm<sup>2</sup>

21.5mm piston cross sectional area = 3.631 cm<sup>2</sup>

Gap cross sectional area = 0.170 cm<sup>2</sup>

Schrader cross sectional area = 0.024 cm<sup>2</sup>

With those sort of tolerances, a 0.5mm gap is far too much - more air can flow from the main chamber to the pilot than out of the pilot through the schrader, so it will never fire.

edit: a 0.25mm difference between piston and chamber diameters still leaves you with a 0.086 cm<sup>2</sup> gap, four times the flow of a schrader.

I suggest using a cast epoxy piston directly in order to guarantee a good fit.

A smaller pilot chamber will improve efficiency and performance, but it will not make it more likely to fire if the gap is too big.
  • 0

Last edited by jackssmirkingrevenge on Sat Aug 20, 2011 9:58 am, edited 1 time in total.
User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Alster370 » Sat Aug 20, 2011 9:57 am

I might just cast an epoxy piston, but if the ID is 20mm then I can get some precision 20mm steel pipe for a super tight fit. And I believe metal on metal will slide better?
  • 0

User avatar
Alster370
2nd Lieutenant
2nd Lieutenant
 
Posts: 243
Joined: Mon Feb 21, 2011 9:34 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sat Aug 20, 2011 10:06 am

You can also have a solid epoxy piston with the rubber seal on the barrel, here's one such launcher I had made:

Image

Epoxy poured into cut down syringe

Image

Piston popped out before finishing

Image

Components before final construction (20mm cannon cartridge is just there for scale ;D)

Image

Actual final construction
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Alster370 » Sat Aug 20, 2011 10:24 am

I thought epoxy didn't slide very well even with grease?
  • 0

User avatar
Alster370
2nd Lieutenant
2nd Lieutenant
 
Posts: 243
Joined: Mon Feb 21, 2011 9:34 am
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: wyz2285 » Sat Aug 20, 2011 10:31 am

it slides well actually in my cases :lol:
  • 0

User avatar
wyz2285
Major General
Major General
 
Posts: 2244
Joined: Sat Mar 06, 2010 7:50 am
Location: Porto, Portugal
Country: Portugal (pt)
Reputation: 12

Unread postAuthor: Alster370 » Sat Aug 20, 2011 10:34 am

Probably just my stuff, has friction like rubber when you touch it. :D
  • 0

User avatar
Alster370
2nd Lieutenant
2nd Lieutenant
 
Posts: 243
Joined: Mon Feb 21, 2011 9:34 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sat Aug 20, 2011 10:37 am

This is proper marine epoxy, hardens like acrylic when cured.

You could always ask someone to machine it for you ;)
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Alster370 » Sat Aug 20, 2011 10:44 am

I was going to do that but moneys tight these days :P. Hot wired doesn't live too far from me, does he have a lathe?

So are you saying I should go with an O ring piston?
  • 0

User avatar
Alster370
2nd Lieutenant
2nd Lieutenant
 
Posts: 243
Joined: Mon Feb 21, 2011 9:34 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sat Aug 20, 2011 10:53 am

Alster370 wrote:I was going to do that but moneys tight these days


It's a small job, in terms of time and material. I think most people will charge you more for postage than the actual piston! No harm in asking for a quote ;) it's important to give the exact internal diameter of the chamber though, you'll need a vernier caliper.

Hot wired doesn't live too far from me, does he have a lathe?


Not to my knowledge.

So are you saying I should go with an O ring piston?


No, a tight fit should suffice.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Alster370 » Sat Aug 20, 2011 10:56 am

Well I think Il wait for some info from the supplier on the exact dimensions of their steel pipes. Should they not be a tight enough fit, Il get a piston machined. Have you any thoughts on the other parts of my design?
  • 0

User avatar
Alster370
2nd Lieutenant
2nd Lieutenant
 
Posts: 243
Joined: Mon Feb 21, 2011 9:34 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sat Aug 20, 2011 11:00 am

Alster370 wrote: Have you any thoughts on the other parts of my design?


It reminds me of some of my early coax designs, what's not clear is calibre, dimensions, pressure and how exactly you intend to put everything together - looks more like a vague concept than an actual blueprint.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Alster370 » Sat Aug 20, 2011 11:08 am

Well im not as graced in using paint as some of the users on this forum are. :D It is more of a concept anyway.

Pressure: 600 psi
Calibre: 6 or 10mm haven't decided yet (same fps anyway according to GGDT, probably better flow.)

Im assembling it will epoxy as last time but using jb weld instead of permatex permapoxy.

I haven't decided on final dimensions as of yet.
  • 0

User avatar
Alster370
2nd Lieutenant
2nd Lieutenant
 
Posts: 243
Joined: Mon Feb 21, 2011 9:34 am
Reputation: 0

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'