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6" diamiter chamber?

A place to ask general spud cannon related questions.
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Unread postAuthor: v3ngence » Wed May 04, 2005 10:02 pm

It dosen't really matter how strong you think your wood fitting is, it can't compare to a properly glued PVC fitting because it isn't meant for this. When a fitting hardens the connection area is actually STRONGER than the PVC pipe itself. This is they way that it's done by professionals all around the world and there is probably a good reason for it. :wink:
I would much rather spend the money and get that kind of confidence than try to botch something homemade. Not dissing on your botching skillz but in this case I think safety out-weighs the price...
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Unread postAuthor: PhoenixFire » Thu May 05, 2005 9:17 pm

Well the wood's pretty much guaranteed not to shatter, lol. 2 inches is pretty thick and considering it's hardwood it might even be overkill. HOWEVER the screws can rip straight through the pvc pipe. It's because the screws have so little of a cross section that they can act like knife blades and rip straight through.

Lets say you have a potato that you wedge dow so darn tight that it sticks even a little. Propane will produce a peak pressure of about 40 P.S.I, I think, maybe more. Noy let's do some math. The plug is 6 in. that gives it a 3 in radius. By area = (pi)r^2 you get an area about 30ish square inches. At 40 psi you'll have 40*30 or 1200 lbs, oh crap that's bigger than even I thought it would be. well now you divide that by 16 screws. This gives you 75 lbs per screw. Yeah, if your gun doesn't fail now it's going to eventually.
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Unread postAuthor: Cool » Fri May 06, 2005 5:05 pm

I'm not an expert of spudguns, this is only my second one. I'm not sure if the pipe is PVC or ABS. it's some pipe i found lying around (not celular core!) The walls of the pipe is 7mm thick, the wooden ends is 2 Inch tick, and the screws is 60mm or 2,4 Inch long. I'v tested the pipe by hitting it with a hammer, and its not even a mark of where i hit.

I have a 2 Inch barrel on this gun witch i shoot only golf balls with (yeah, its to big, i know) So i dont think the gun will fail on me, i'm only using starting fluid as propelant, so its not as powerfull as propane.

I'l try to to take som pictures of it tomorow, if i get my camera to work.
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Unread postAuthor: PhoenixFire » Fri May 06, 2005 6:37 pm

Allright then. We'll see how long it works. It may actually be just fine but I tend to be on the safe side. One kid in my class, for example made a gun using unregulated CO2 from a 20 oz. tank. He's not dead yet, nor did his gun explode which just shows that it's possible to get away with being unsafe. By the way, the length of the screw doesn't matter as much as the width. The PVC is only 7mm thick and the screw only about 1mm giving you 7mm x maybe 1 mm of space to rest that 75 lbs of force. It's seriously possible that the screws will rip through the PVC not the wood, and shoot a wood cylinder with 16 screws poking out of it out the back.

Yeah starting fluid isn't as powerful as propane mwahaha. I seriously hope that you mean lighter fluid used to ignite charcoal.

If you're using the stuff used in car carbeuratoes (sp?) you're asking for a failure. Since this comes in a can i think theis is what you're using. That stuff is MORE powerful than gasoline. Hell you can actually blow your engine if you use too much. You'd be better off using some pure gasoline in a small spray bottle.
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Unread postAuthor: v3ngence » Fri May 06, 2005 7:48 pm

Never heard of the car starting fluid but it sounds intruiging.... :twisted:
Im pretty sure he's talking about charcol lighter.
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Unread postAuthor: Cool » Sat May 07, 2005 3:22 pm

Its car starting gas, its used to start your car if it wont start.

The screws is about 5mm thick, and ther is 8 screws in each end. Since the wood is 2 inch thick, the screws are far away from eachother, from the last screw and to the end of the pipe, its about 1,5 cm.

Is starting gas more powerfull than propane?
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Unread postAuthor: CS » Sun May 08, 2005 11:32 am

I think starting fluid is more powerful than propane if they both had the perfect mixture. But propane is more powerful usally because it is alot easier to measure and get the "perfect mixture".
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Unread postAuthor: Aaron ????? » Sun May 15, 2005 5:56 am

is the wood all sealed up because wood can leak easily???

but it would cost a hell of a lot to get fittings that size at my local bunnings shop its $12 just for a 5 inch cap with female threads

but that is australian money
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Unread postAuthor: Cool » Sun May 15, 2005 3:36 pm

Yes, its very tight, the are made 1mm to big, så i have to hammer it down.
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Unread postAuthor: Aaron ????? » Fri May 20, 2005 3:24 am

how do you put the fuel in??? with the wood there?????
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Unread postAuthor: spudshot » Fri May 20, 2005 3:29 am

he probably has either a propane injection system or a tapped hole he puts a metal plug in
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Unread postAuthor: No.Va » Fri May 20, 2005 9:02 am

ok, with all the arguing going on, i dont think anyone can geta clear picture of what you have going on, i tink it might just be safe to take a picture so everyone has the same idea of what is actually being used here. who cares if its ugly, it works, that should be good enough!
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Unread postAuthor: boilingleadbath » Fri May 20, 2005 1:35 pm

"better that the PVC" *scoff* Ok, I'm not going to dismis you on first instinct...
Seems the tensile strength of wood is 1,000-3,000 PSI. This varies on moisture content, so I'm going to assume the worst: 1,000. This is 7 times less that that of PVC= 2/7" PVC. This is probably safe. (though NOT better than PVC) Again, it's not exactly the best shape for pressure containment.

However, the bond for the PVC is better - you have 16 measly screws (that's for each end, right?) to hold (possibly over) 1,500 lbs - just under 100 lbs/screw. I don't like the saftey margin... but I'm not going to be able to change you mind - just don't put your head behind it!
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Unread postAuthor: Cool » Sat May 28, 2005 4:03 pm

I'm posting a link to some photos of my cannon.

http://forums.spudtech.com/topic.asp?TOPIC_ID=9545
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Unread postAuthor: Aaron ????? » Mon May 30, 2005 4:33 am

kool that thing is a beast is it abs??????????
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