SpudFiles

I will start out by saying thanks to all of you guys for giving me something to do for the last few weeks. I have stumbled across this hobby on accident and I am pretty much addicted for the moment. I have yet to make any cannon but I am well on my way to deciding just what I will do for a first cannon. I have done the research and it turns out that nobody seems to have used a Sigg bottle for a combustion chamber. So I went to Home Depot today and found a few items that are/could be the initial building blocks of my first cannon.

I must say that while many of the cannons I have seen are completely amazing and huge and great, I do not like pvc at all. LOL huh? SO I began, very early in my interest, trying to find alternatives for pvc. My Sigg ottle seems to be the perfect size for a small, entry level cannon but it poses a few obvious hurdles. The first of which is how do I attach a barrel to the thing. Problem solved.

I found a perfect fit for the threads on the mouth of the bottle (garden hose adapter) and can now screw in a 1/2"X12" pvc nipple to be used as a barrel. Also, since the threads fit perfectly and the garden hose adapters are available in different sizes, I can exchange barrels without even using a tool.

Please check out the pics and let me know if I am just nuts. The bottle is a 20 oz type ad Sigg also makes a 1.5 liter bottle that could be used as well.

edit:
The obvious next hurdle is how am I going to get the propellant into the chamber. Still working on that one. Problem is that the bottle is pretty thin. I'll figure it out soon enough. I would like to use propane and I think it would be much easier than trying to remove a cap and spray fuel into it after each shot. ONce I figure out all the details I will mount that joker onto a snazzy handle recycled from something in the garage, but it will not likely be a pvc handle.

edit by MrCrowley: Don't double post.

Great discovery! No doubt someone will here will find this useful. All someone needs to do next is pressure test one of these. Even if it's not used for pressure, it's good to know I can connect something to my Sigg bottle.

LOL. True. Seems pretty solid. I think they are extruded so they don't have a seam. I don't see why it couldn't handle a small combustion. If it helps, there is a PVC piece that fits the bottle as well. I just hate that junk so I searched for the brass. Since that is a hose adapter, I am sure there must be a way to pressure test the bottle using water right?

If anyone is thinking of using CO2 in one, don't. Apparently they crack at low temperatures. Just saying

How high is the air pressure rating? It looks good to use for a little pneumatic... It looks cool too

Not sure, I figured I'd just hope for the best.

Hah I agree, better hope its pretty high though

Maybe getting another one and pressure testing it yourself would be a good idea...

If I were you I wouldnt use it... I have dented aluminum bottle like these with a crappy bb gun... and trust me it made a huge dent and almost went through ... I wouldn't trust these at more than 40 psi, maybe less..

I guess without having onevtested we can do only a couple things: try it, test it or guess based on other things' pressure ratings. For instance, a typical coke can at rest has an internal pressure of 50 to 55 psi. I've read that the pressure increases greatly when the can is shaken. So I'd guess the can is probably rated for around 100 psi given that those things at delivered all over the world and in different climates. The pressure in the can increases with the temp.

I'm just going to try it out myself.

I'd feel safe with it as a combustion, perhaps even fuel metered combustion. If the bottle starts to bulge, then I would chuck it away. If it could hold 100PSI all night without bulging, i'd feel safe with it as well.

My opinion about sigg bottles -> DON'T

The Aluminium that it is made of is simply to soft and the threads are to fine for standard fittings. I used one on my first pneumatic and the bottle became loose at 120psi, shooting like rocket against my knee.

It hurt so bad that I thought my kneecap was shattered.

Sorry to hear about your knee. I wouldn't blame the bottle for you having chosen the wrong fitting though. The thin-ness or softness of the aluminum has nothing to do with the fitting breaking loose. You just need a fitting that, well... Fits. This one is a 3/4" hose fitting and it fits like a champ. It's not air tight, but what is without the use of Teflon tape or a gasket? I say it's all good if you got to 120 psi and the only thing that failed was your fitting.

There isn't a "right fitting".

It's a drink bottle, not a pressure vessel. It's not designed to be compatible with airlines or pressure water systems. It wasn't made with the intention f holding pressure.

To think that the fitting is the right one and they are a perfect pressure vessel is the wrong fitting. The bottle is made to hold a few " of H2O of pressure, not 120 psi. The aluminum is thin, and it will be made from an alloy that is cheap and easy for them to work.

If you want to test it, great. If your happy with it and want to use it, great. Don't assume it was intended for this though.

These bottles/threads are not made to take standard fittings. I've used a brass fitting the same like you do and it "looked" extremely solid.

Getting it airtight is another story. Even with loads of teflon tape and a gasket it was a pain. It's simply not worth it.

MrCrowley wrote:If anyone is thinking of using CO2 in one, don't. Apparently they crack at low temperatures. Just saying

Apparently IIRC Aluminum got this property that it becomes more ductile at cryogenic temps instead of brittle like lots of other things.


Ooh just checked, seems I am correct

Below zero, most aluminum alloys show little change in properties; yield and tensile strengths may increase; elongation may decrease slightly; impact strength remains approximately constant. Consequently, aluminum is useful material for many low-temperature applications.

from http://www.keytometals.com/Article23.htm

PS. I am not implying that using one of these containers would be safe at high pressure