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m72 LAW Design questions

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: jackssmirkingrevenge » Fri Jul 27, 2012 5:45 am

Zeus wrote:JSR, it's 550 paracord, it's practical and manly...


This is a manly use of paracord:

Image

:D :D :D
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Unread postAuthor: Zorlord » Fri Jul 27, 2012 12:35 pm

jackssmirkingrevenge wrote:When you can't afford the best tools or materials, you need to be a little creative. Here's what I had done using a piston from a ordinary cheap-o footpump to make a toolies piston: http://www.spudfiles.com/forums/viewtop ... tml#304901

Also, that bracelet.

Image

:D


Image

My younger brother made it for me. I would have it in a more tacticool color, but for whatever reason he only had yellow and orange lol.

And the rubber bits on the front are just rubber neoprene washers from home depot. i have 2 1" and one 1 1/2 inch ones on there, all sandwiched together.

EDIT:

JSR, would creating a hot glue piston with a rubber gasket sealing face be adequate for my piston? I just went out and purchased some marine epoxy, but id rather practice/use something cheaper first in case i screw up.
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Unread postAuthor: Live1nce » Fri Jul 27, 2012 5:13 pm

I wonder if picking up a sheet of plastic cutting board from wal-mart will work. It's about a half inch thick, very easy to cut, and is very strong. I'm sure you could make about 20-25 pistons from it.

I've used it before for my slide gloves for longboarding, and when i think about it, it should work perfect. http://www.youtube.com/watch?v=-OfgaMBtdTk

In that video it shows what the plastic cutting board looks like. It says he got it at lowes, but i've never checked there for it, I always got it at wal-mart.
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Unread postAuthor: Zorlord » Fri Jul 27, 2012 6:00 pm

Live1nce wrote:I wonder if picking up a sheet of plastic cutting board from wal-mart will work. It's about a half inch thick, very easy to cut, and is very strong. I'm sure you could make about 20-25 pistons from it.

I've used it before for my slide gloves for longboarding, and when i think about it, it should work perfect. http://www.youtube.com/watch?v=-OfgaMBtdTk

In that video it shows what the plastic cutting board looks like. It says he got it at lowes, but i've never checked there for it, I always got it at wal-mart.


I'll go look after work.. I have a 24 hr wally world by me that would probably have it.. Now I just need a jigsaw.. Don't think my dremel or hand saw is gonna cut it
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Unread postAuthor: Zeus » Fri Jul 27, 2012 7:35 pm

HDPE is ideal for piston bodies, and sealing faces at very high pressures, but good luck getting it to seal at low pressure (<3-400psi).

Making the piston out of hot glue might cause problems, it can crack quite easily. Have a look at Tech's o ring piston tutorial in the How To section. Unlike JSR, I know epoxy is good, but it has some limitations.

Good to see some intelligent new members around, even if they're talking about pneubmatics.
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/sarcasm, /hyperbole
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Unread postAuthor: Live1nce » Fri Jul 27, 2012 8:55 pm

For some of you more experienced members... I understand the importance of having a light weight piston especially with a design like this, But what is the likely hood of the cannon accidentally firing if it was ever to be dropped on its rear end on some solid surface, ie concrete.

Would the piston pop lose from the barrel seal and fire? You may want to take this into consideration zorlord. I know with airsoft, this thing will probably get banged around quite a bit.
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Unread postAuthor: Zorlord » Fri Jul 27, 2012 9:16 pm

Zeus wrote:HDPE is ideal for piston bodies, and sealing faces at very high pressures, but good luck getting it to seal at low pressure (<3-400psi).

Making the piston out of hot glue might cause problems, it can crack quite easily. Have a look at Tech's o ring piston tutorial in the How To section. Unlike JSR, I know epoxy is good, but it has some limitations.

Good to see some intelligent new members around, even if they're talking about pneubmatics.


I did see his tutorial.. Unfortunately i don't have access to a drill press.. Also, where does everyone find 2 inch orings? i cannot find them anywhere local.

EDIT:

For materials, could i use fiberglass resin to make my piston? I bought some for another project i have going on, and it's a lot cheaper than epoxy.. used the entire syringe of epoxy to make a small piston.. and the syringe was about 5 dollars... i guess i should be buying the stuff in the bottles instead of the small packs..
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Unread postAuthor: jackssmirkingrevenge » Sat Jul 28, 2012 3:37 am

Zorlord wrote:My younger brother made it for me. I would have it in a more tacticool color, but for whatever reason he only had yellow and orange lol.


Maybe it was a cunning trick and he was trying to provoke the "gaaaay!" reaction :D

I was of course joking, no offence intended ;)

JSR, would creating a hot glue piston with a rubber gasket sealing face be adequate for my piston? I just went out and purchased some marine epoxy, but id rather practice/use something cheaper first in case i screw up.


I'm guessing you've seen the tutorial: http://www.spudfiles.com/forums/making- ... t8919.html

There's pretty much everything you need to know there, have a good look.
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Unread postAuthor: c9d » Tue Jul 31, 2012 1:08 am

I went and bought a decent thickness HDPE smooth cutting board an cut out a few circles with differing diameter hole saws. I just had to use a center bit the same size as my rod. As long as you keep the cutting board very stable while cutting the pieces out of it, and round burrs from the edges with a very sharp knife... you should be good
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Unread postAuthor: Zorlord » Tue Jul 31, 2012 11:55 am

update!

well, I decided to make a resin piston.. Cut a short piece of 2" pvc, coated the inside with a thin layer of petroleum jelly, then mixed up some resin and poured it in. here's the finished result:
Image

And as you can see, it fits fairly well inside the chamber:
Image

now i just need to drill a hole through it and attach it then HOPEFULLY this thing will work
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Unread postAuthor: Live1nce » Tue Jul 31, 2012 2:04 pm

That piston looks great! do you know around how much that piston cost you in resin material?

I just finished my solenoid canon, but i'm headed off to Lowe's today to pick up some more parts for a piston cannon.
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Unread postAuthor: Zorlord » Tue Jul 31, 2012 9:01 pm

Live1nce wrote:That piston looks great! do you know around how much that piston cost you in resin material?

I just finished my solenoid canon, but i'm headed off to Lowe's today to pick up some more parts for a piston cannon.


Unfortunately no. I used the resin that's meant for fiberglass repairs and such. I bought the biggest container they had because i'm using it for other projects, and i think it was around 20 bucks? dont remember off the top of my head. But i used 4 oz of the resin and then 40 drops of hardener. Then i mixed it in a cup and poured it into a scrap piece of 2" pipe that had the inside coated with petroleum jelly. let it dry then i got that.
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 31, 2012 9:48 pm

Zorlord wrote:now i just need to drill a hole through it and attach it then HOPEFULLY this thing will work


Drill a hole why? For the bolt to attach the rubber I hope, you dont need an equalisation hole.
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Unread postAuthor: Zorlord » Wed Aug 01, 2012 12:11 am

jackssmirkingrevenge wrote:
Zorlord wrote:now i just need to drill a hole through it and attach it then HOPEFULLY this thing will work


Drill a hole why? For the bolt to attach the rubber I hope, you dont need an equalisation hole.



haha yes, to attach the bolt/rubber.

Also, has anyone thought of making these into projectiles? i feel like theyd do some damage..
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Unread postAuthor: Mr.Tallahassee » Wed Aug 01, 2012 2:44 am

Live1nce wrote:For some of you more experienced members... I understand the importance of having a light weight piston especially with a design like this, But what is the likely hood of the cannon accidentally firing if it was ever to be dropped on its rear end on some solid surface, ie concrete.

Would the piston pop lose from the barrel seal and fire? You may want to take this into consideration zorlord. I know with airsoft, this thing will probably get banged around quite a bit.
To answer this since I don't think it ever was, The pressure against the piston creates enough force that dropping the gun theoretically shouldn't cause it to pop loose and fire. I would be more worried about the body shattering if it's made of pvc, that could be worse than the piston actuating. Unless you make a valve with a seat diameter that's ridiculously close to the piston diameter, I wouldn't be too concerned.
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