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6 inch coaxial

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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6 inch coaxial

Unread postAuthor: joestue » Sat Jun 14, 2008 11:37 pm

This was my first cannon, i made a few mistakes the first time, but maybe a year later when back home again, I will upgrade it, with a composite wrapped chamber, aluminum valve, and fire it at 300 psi.

I don't have any damage shots, but the speed is as good as an ideal valve +/-10%, as per GGDT simulation, this I was able to measure.

A few details, the rest are in the .PDF inside the .rar file.

6 inch white pvc, five foot long chamber, rated to 100 psi by my calculations, the barrel is inside of course, it's coaxial.

The valve is the weak point, but please don't respond in error until you read the entirety of the pdf, it's safer than it looks.

With a 9 foot long extension to the 5 foot long barrel, things are really interesting to say the least...

overall cost was about $15 for 2 bottles of glue, 4 2 inch and 2 1.5 inch end caps, the rest i had already.

Photos here: http://s299.photobucket.com/albums/mm294/johansense/


Edit by MrC: Pictures added and same with what was said in the PDF for safety reasons:

-Notes behind the design-
I built this pneumatic cannon hastily over two weeks of leave at my parent's house, 2007Dec-Jan08.
Originally I had planned on casting an aluminum reducer, but the wax mold proved too much work so
I just added more reinforcing plastic to the end caps, with extra on the valve side for safety.
The barrel is 2 inch white pvc, rated at 300 psi, 4 feet long, coupled to a 24 inch long cellular core,
black PVC pipe. (Because that's what I had). The coupling is inside the chamber.
Two sets of radial spokes were glued to the barrel.
The valve is 1.5 inch cellular core PVC. 1 'o' ring is used to seal the pipe to the end cap. Several 1.5
inch dia. end caps were cut to produce several rings, one on each side of the end cap, permanently
sealing the O ring inside. One ring and rubber disk forms the valve seat.
As shown in the bitmap drawing, the 6 inch diameter end cap is cut, and a 2 inch length of 6 inch pipe
is glued to the inside of it (this is what the spokes are glued to).
The cut off part of the end cap was glued to the 5 foot long pipe with the intention that the two could be
bolted together, and disassembled as desired.
Murphy's law says DIY pipe couplings leak and it did.
Originally I screwed the valve to the end-cap-pipe-coupling with 36 short wood screws.
-I don't know where I got that idea-
Of course it leaked, but a little water dumped into the chamber would temporarily seal all the holes.
The difference in area between the inside of the 2 inch dia barrel and the outside of the 1.5 inch dia
valve is what pushes on the valve seat. Below 30-50 psi, this isn't enough, and about 50 pounds of force
was needed to seal the valve, when filling with air.
The plastic reducer exploded at 70 +/-5 Psi after a few launches, taking the black PVC portion of the
barrel at the coupling with it and got launched a few hundred feet into the air.
A few changes...
The reducing end cap was replaced with vacuum degassed cast aluminum . It's about 1/8th inch thick at
the thinest part. The ring holding the aluminum back, glued to the inside of the chamber is 1 inch wide.
The barrel was centered/supported with 4 sets of radial spokes, (the slight curve in the pipe caused the
joint to crack, causing some of the air leak, this was obvious looking at the glue).
To the valve was added the reinforcing spokes, and to these spokes was glued 1/8th inch thick triangular
PVC pieces. (Not shown in the photo.) The valve seat was rebuilt and ground with a corundum based
valve seat compound so it seals much easier. (The photo of the valve doesn't show the new valve seat,
nor the aerodynamic piston face).
Other notes: the spokes and triangular pvc reinforcement were cut from a pvc Apple II housing, it's a
little softer than PVC pipe, but thats a good thing, because the flat end cap still flexes outward about
1/16th of an inch @ 65 psi. I should have made an aluminum valve, but I don't have a lathe yet.
To be added is an air activated valve, by encasing the piston in a pipe, and adding an air valve, all you
would have to do is pull a trigger activated valve and piston response time would be pretty much zero.
As it is now, a rope is used to absorb the shock of the piston traveling backwards, and another cord and
a 5 pound weight is used to pull the piston back.
I do not intend to pressurize it beyond 100 psi, because 2 inch pipe is rated at 300 psi.
If I wrap the entire 5 foot long chamber in a 10+ layers of pretensioned epoxy/aluminum foil, or one
layer of 19 gauge bailing wire, 200-250 psi should be safe, assuming an aluminum piston.
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Attachments
spud.rar
10 photos, a cut away diagram, and too many details.
(725.67 KiB) Downloaded 108 times
a.jpg
b.jpg
b.jpg (23.05 KiB) Viewed 1931 times
c.jpg
Last edited by joestue on Sun Jun 15, 2008 12:39 am, edited 1 time in total.

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Unread postAuthor: starman » Sat Jun 14, 2008 11:52 pm

Not everyone has a .rar expander. Why don't you just post the pictures at imageshack and link to them.
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Unread postAuthor: Carlman » Sun Jun 15, 2008 12:23 am

interesting... :D

so is it a normal coax now or do you still yank er back?
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Unread postAuthor: joestue » Sun Jun 15, 2008 12:26 am

still got to snap it back with a 3 pound lead block

unless my brother worked on it, it's still the same
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Unread postAuthor: TheTrooper » Sun Jun 15, 2008 12:27 am

Wow good job joestue you really did your research
Just two things, first, that gun doesn't look very safe from the pictures buts thats just me. Second: just upload your images to image shack then upload here its much easier.

Edit: Never read the Adobe article, did not know it was made of bad materials.
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Last edited by TheTrooper on Sun Jun 15, 2008 1:41 pm, edited 1 time in total.
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Unread postAuthor: MrCrowley » Sun Jun 15, 2008 12:41 am

My word that is the most unsafe cannon I have ever seen.

It's pretty much built from cellular core PVC and ABS and you want to take it to 250psi :shock:

I'm surprised the whole thing hasn't already blown up. You've done some research but completely left out the part about safety.

Just because you reinforce the chamber to stop the shrapnel hurting you doesn't mean it's safe, it still will explode.

I would cut this thing in 4 pieces and bury them at the four corners of the earth, I know you think it's safe, but it ain't.

One small knock, and everything is gone....into your body.

I do not recommend the use of this cannon, ever. I don't care if you listen to me or not, but it's not safe.
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Unread postAuthor: joestue » Sun Jun 15, 2008 12:50 am

lol
-classic look at first photo ignore the rest..... response

dude chill out

more details: the most the valve was exposed to was 70 psi, after the other side exploded at 65 psi, and i added more pvc to it

I'm taking it to 300 psi after replacing the valve with a cast aluminum reducer, and wrapping the chamber.

only the last two feet hear the end is black cellular core, because i didn't want to buy 10 feet more.

and i'd rather have it fail there first....
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Unread postAuthor: MrCrowley » Sun Jun 15, 2008 12:57 am

I read the whole stupid PDF thanks mate.

The fact that it blew at only 70psi tells me something. Has this been to 100psi? My bet it wont make it because of the cheap DWV fittings and cell core pipe on it.

There's a reason they blew out. Adding more PVC to it wont do much.

The fact that you spend $15 on it tells me something else also, you're cheap and don't give a rats ass about safety.

The chamber will still fracture and fittings will still fail.

only the last two feet hear the end is black cellular core, because i didn't want to buy 10 feet more.

Oh no, can't waste $5 now can we? I spend a ridiculous amount on cannons because of the prices in NZ, and you can't spare $5 for safety in the land of cheap PVC.

If this cannon was built properly it would cost you over $100. You're just wasting money trying to make it safe, the performance would be far better if you built it properly too.
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Unread postAuthor: TheTrooper » Sun Jun 15, 2008 1:01 am

MrCrowley you need to show him the video of the PVC chambers exploding and the 2-liter bottle going off, if only i knew the links, do you?
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Once people start building spud guns they have two career options, they can be a weapons designer or a plumber. Hard choice isn't it.

Projects Completed:
http://www.spudfiles.com/forums/viewtop ... tml#148488

http://www.spudfiles.com/forums/viewtop ... tml#190652
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Unread postAuthor: joestue » Sun Jun 15, 2008 1:06 am

The flat plastic reducer failed at 65 psi, i then replaced it with aluminum.

The chamber is rated to 100 psi, it don't say that on the side, but the 2 inch stuff is rated to 300, so by analogy...

the valve as is would hold 100 easy, the flat reducer failed around the edges, where the flat pvc meets the 2 inch long 6.5 inch diameter ring, where the sheer stress is highest, where the glue didn't get to.

edit: the barrel is solid white pvc, unlike some, it doesn't have 2 separable layers.
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Last edited by joestue on Sun Jun 15, 2008 1:15 am, edited 1 time in total.

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Unread postAuthor: MrCrowley » Sun Jun 15, 2008 1:10 am

The chamber is probably cell core or DWV, just because the barrel is rated to 300psi doesn't mean the chamber is 1/3rd that.

That is very bad logic.

The barrel is made to pressure standards, the chamber is made in a way that it isn't rated for pressure. So you can't simply divide by 3 when the pipe is completely different.
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Unread postAuthor: TheTrooper » Sun Jun 15, 2008 1:10 am

The chamber is rated to 100 psi, it don't say that on the side, but the 2 inch stuff is rated to 300, so by analogy...


Thats horrible reasoning, the chamber could be made out of a completely different material than the fittings are.

Edit: How do you like my new Profile Picture 8) ?
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Once people start building spud guns they have two career options, they can be a weapons designer or a plumber. Hard choice isn't it.

Projects Completed:
http://www.spudfiles.com/forums/viewtop ... tml#148488

http://www.spudfiles.com/forums/viewtop ... tml#190652
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Unread postAuthor: MaxuS the 2nd » Sun Jun 15, 2008 3:59 am

Dude, I can't believe how you're actually arguing with safety.
DWV, Cell Core and ABS are not safe....End of.
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Unread postAuthor: Carlman » Sun Jun 15, 2008 3:59 am

you better listen to MRCROWLEY mate, there has been a number of accidents relating to the use of DWV and drain pipe, which ven lead to the loss of sight in one of the guys eyes.
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Unread postAuthor: MrCrowley » Sun Jun 15, 2008 4:13 am

Yes that is true, we had a member who's father lost an eye after a PVC chamber failure. Not to mention the fact that 7 other people were also injured.
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