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 66 users online :: 3 registered, 0 hidden and 63 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

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

The Team
Administrators
Global Moderators
global_moderators.png CS

plywood piston

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

plywood piston

Unread postAuthor: judgment_arms » Fri Oct 20, 2006 1:58 pm

Greetings all,
I have come here in order to tap into the vast and semi-limitless knowledge of Spud-files!
Ok, now on more serious note. Do you guys know if plywood will work for a piston?
I’m planning on making a coaxial air cannon soon and was trying to figure out what to use for the piston. In addition, I would also like to know if inner-tube rubber will work instead of neoprene for seals.
  • 0

User avatar
judgment_arms
Major General
Major General
 
Posts: 1272
Joined: Tue Oct 17, 2006 8:49 pm
Location: Not so beautiful North Carolina, but at least it’s the U.S.A.!
Reputation: 0

Unread postAuthor: joannaardway » Fri Oct 20, 2006 2:35 pm

There might be problems with using plywood - wood is slightly porous. Plywood even more so. Try something else.

Inner tube rubber might work - I've used it before, but it is a little too thin to really seal anything but a nearly perfect fusion of piston and sealing face. Using multiple layers isn't very good either.
  • 0

User avatar
joannaardway
Brigadier General
Brigadier General
 
Posts: 949
Joined: Mon Oct 09, 2006 4:57 pm
Location: SW Hertfordshire, England, UK.
Reputation: 0

Unread postAuthor: judgment_arms » Fri Oct 20, 2006 2:40 pm

Yes it’s porous but don’t you drill bleed holes in it anyway?
Plus if you paint it, it ceases to be porous.
  • 0

User avatar
judgment_arms
Major General
Major General
 
Posts: 1272
Joined: Tue Oct 17, 2006 8:49 pm
Location: Not so beautiful North Carolina, but at least it’s the U.S.A.!
Reputation: 0

Unread postAuthor: joannaardway » Fri Oct 20, 2006 2:51 pm

Plywood is also very brittle - it won't stand up to the massive forces in a piston valve.
  • 0

User avatar
joannaardway
Brigadier General
Brigadier General
 
Posts: 949
Joined: Mon Oct 09, 2006 4:57 pm
Location: SW Hertfordshire, England, UK.
Reputation: 0

Unread postAuthor: schmanman » Fri Oct 20, 2006 2:55 pm

jrrdw did it without a problem.
  • 0

Persistence is a measure of faith in yourself
User avatar
schmanman
Major General
Major General
 
Posts: 1685
Joined: Sat Mar 25, 2006 12:28 pm
Location: Michigan,U.S.A
Country: United States (us)
Reputation: 0

Unread postAuthor: judgment_arms » Fri Oct 20, 2006 3:05 pm

Plywood is used in sailplanes, boats, housing, and a plethora of other applications requiring lots of strength. Plywood is by no means brittle. I mean no offence to you my friend, you my have bean mistaken or, perhaps you thought I was talking about OSB or fiber board.
  • 0

User avatar
judgment_arms
Major General
Major General
 
Posts: 1272
Joined: Tue Oct 17, 2006 8:49 pm
Location: Not so beautiful North Carolina, but at least it’s the U.S.A.!
Reputation: 0

Unread postAuthor: MrCrowley » Fri Oct 20, 2006 3:08 pm

how thick is the plywood?
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Sponsored

Sponsor
 


Unread postAuthor: judgment_arms » Fri Oct 20, 2006 3:13 pm

It all depends on what I can get but it shall be at lest two inches thick.
Is that enough or do you believe it should be thicker?
  • 0

User avatar
judgment_arms
Major General
Major General
 
Posts: 1272
Joined: Tue Oct 17, 2006 8:49 pm
Location: Not so beautiful North Carolina, but at least it’s the U.S.A.!
Reputation: 0

Unread postAuthor: djt » Fri Oct 20, 2006 5:19 pm

two inches sounds plenty. and about the porous thing, you have to put a piece of neoprene or something on the face of the piston anyway and the rubber wont be porous
  • 0


djt
Major
Major
 
Posts: 387
Joined: Sat Mar 11, 2006 4:30 pm
Reputation: 0

Unread postAuthor: joannaardway » Sat Oct 21, 2006 1:18 pm

Ok, this is a simple question I and my twin use to help decide if a material is suitable for a piston:

"Would you trust (whatever) to be part of your chamber wall?"

If not, then don't use it - it's either not air tight enough, or too brittle. Would you use plywood as part of your chamber wall? I would assume not.

Believe me, the forces in a piston valve are huge. Even a small 20mm seated one has about 85 pounds of force on it at a typical working pressure. That boils down to an equivalent "pressure" on the surface of the piston (where the seat touches it) of about 923 psi.

Which is a helluva lot.
  • 0

User avatar
joannaardway
Brigadier General
Brigadier General
 
Posts: 949
Joined: Mon Oct 09, 2006 4:57 pm
Location: SW Hertfordshire, England, UK.
Reputation: 0

Unread postAuthor: judgment_arms » Sat Oct 21, 2006 1:29 pm

Um… the utopia guy used hot glue. And about the not being air tight once again don’t you drill bleed holes in it plus there is a rubber seal between the piston and the barrel.
923 PSI!?! Who taught you math. I’m only running the thing at a 100PSI.
  • 0

User avatar
judgment_arms
Major General
Major General
 
Posts: 1272
Joined: Tue Oct 17, 2006 8:49 pm
Location: Not so beautiful North Carolina, but at least it’s the U.S.A.!
Reputation: 0

Unread postAuthor: djt » Sat Oct 21, 2006 1:52 pm

i think hes trying to say 923 pounds of force because it would be 100 pounds PER square inch. but i doubt you would have 9 square inches
  • 0


djt
Major
Major
 
Posts: 387
Joined: Sat Mar 11, 2006 4:30 pm
Reputation: 0

Unread postAuthor: Brian the brain » Sat Oct 21, 2006 2:53 pm

The Chappy cannon used MDF for it's piston.
The set up was like a washer and bolt kind of piston.We used the MDF as washers.

It worked but gave out at about 20 shots.It broke beyond repair, so now it has 8 mm aluminium "washers" and it works like a charm now.

Of course, the thickness was onlu 1/2 inch so 2 inch should work.
  • 0

Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
User avatar
Brian the brain
Moderator
Moderator
 
Posts: 3494
Joined: Mon Dec 05, 2005 2:06 am
Location: Holland
Country: Netherlands (nl)
Reputation: 29

Unread postAuthor: Infernal2 » Sat Oct 21, 2006 2:55 pm

Wood works fine for pistons. Sure, there is unbelievable pressure placed on wood but remember, wood is the most commonly used building material on the earth for a reason. Wood is both plentiful and durable.

For example, a 5/8 piece of oak, painted with an oil based acrylic and then lubricated is a very effective piston. The acrylic does readily seal the wood.
That said, plywood is an awful composite for a piston. Ply wood is (depending on width) two to three layers of slat over OSB composite (dried pulp). It is not very strong and should not be used.

You can use it but I personally wouldn't. If it does shatter you will be cleaning wood out of every working part in your gun. Think, a possibly punctured diaphragm, sealing face....etc...

Stick with solid hardwoods.
  • 0


Infernal2
Staff Sergeant
Staff Sergeant
 
Posts: 122
Joined: Mon Sep 11, 2006 9:38 pm
Reputation: 0

Unread postAuthor: judgment_arms » Sat Oct 21, 2006 3:39 pm

Never seen anything like you described all the plywood I’ve got is thin sheets of wood layered together. I think I’ll take my risk and go with plywood I’d trust that a little bit more the hot glue or some of the other things people have used.
Thanks all
  • 0

User avatar
judgment_arms
Major General
Major General
 
Posts: 1272
Joined: Tue Oct 17, 2006 8:49 pm
Location: Not so beautiful North Carolina, but at least it’s the U.S.A.!
Reputation: 0

Next

Return to Pneumatic Cannon Discussion

Who is online

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

Reputation System ©'