3" piston ideas

[Shrimphead]

I need some ideas of what to make a piston out of for my 3" chambered cannon. I need an idea that would be simple and cheap to make, that wouldn't require any special tools (e.g. lathe) and that would work very effectively
Thanks in advance

[saladtossser]

http://www.spudfiles.com/forums/viewtopic.php?t=304

[Shrimphead]

I've seen that one before. I tried to make one out of a can, but I'm having trouble with it. Will one made out of 2 2.875 in" metal washers and 2 3" rubber washers connected by a bolt and some nuts work?

[jrrdw]

make it out of plywood bike inner tube bolt washer, it will be custome that way, and you get to build it from scratch

[Shrimphead]

So the washers will be the part thats sliding in the chamber?

[jrrdw]

The entire piston will slide. It has to. The warshers help keep the rubber seal from blowing off out through the barrel. Make sure you place stops to block the piston, or it will more then likely get busted up one way or another.

[Shrimphead]

I know that the whole piston slides. I want to know which part of the piston is actually rubbing the inside of the chamber walls as the piston moves.

[theregoesthewindow]

The rubber rubs against the wall. Notice jrrdw said "rubber seal"

[Shrimphead]

I thought that rubber was to seal against the barrel

My dad went to HD yesterday to pick up some parts, and he said that the biggest neoprene washer they had was only 2.5". He also said that they didn't have any metal washers near 3". Does anyone know if lowes carries neoprene and metal washers around 3"?

Edit- I went to Lowes today and the largest fender washer was 2.5". Does anybody know where I could get one 3"? And also, if I can't get one, how then would I make the piston??

Jrrdw, could you draw up a quick sketch in paint to show me what you are talking about? I'm a little confused. I really need to get a working piston on this thing, I've been working on it since christmas, but I've never been able to make a piston that seals correctly against the barrel!!!

[nicholai]

/\ /\ /\ /\ /\ /\ /\ /\
triple post mods are gonna get mad at ya, go back and edit your first post to include the other two, then delete the other two

try putting a decent strength spring on the ass end of the piston

the rubber seals the front of the piston(either to the barrel or the chamber, in your case the barrel) and also acts as a shock absorber on the back side.

http://www.spudfiles.com/spud_wiki/inde ... ston_valve

look at the ms paint picture on that link, the top diagram shows how a piston should seal a barrel, it holds pressure on BOTH sides of the piston, this is important to remember that if your piston is going to seal by a spring instead of pressure it must have a calibrated leak to allow the back of the piston to pressurize in order for it to actuate by a pressure drop in the back end.
the bottom diagram shows what happens when a piston is "actuating", the release of pressure makes the piston break the seal, since it will flow faster through the barrel this causes the piston to rocket backwards and equalize the pressure, the resulting energy slams the piston back.

The space behind the piston is the pilot, the size of this and the weight of the piston determines how fast your homemade valve will actuate

[cardinals08]

http://www.spudfiles.com/forums/viewtopic.php?t=313
here is a how to on this site for 3" piston

[nicholai]

thanks dude, i knew you'd find it before i did

[Shrimphead]

I pasted the second two into the first, but I don't know how to delete them.
^^^^^^^^^^^^^^^^^^^^^^
The "delete" button? -Pimpmann22

Nicholai- I totally understand how pistons work, it's just making a working on that is the problem.

Cardinals- I am considering making the piston in that link, the two things I'm worried about are:
1. I don't know where to get sheet pvc and how much will it cost?
2. Cutting the o-rings on the drill press. I should be able to get it right, but it would be a lot easier on a lathe.