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Aluminium, is it safe?

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: SEAKING9006 » Thu Oct 16, 2008 9:22 pm

I wish I had the tools to machine aluminum to fine tolerances.


If I did, you would be seeing a hell of a lot of mechanical designs out of me.



And yes, mechanical means automatic. :D
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Completed projects:
CA1 SMSS Basic Inline
CA3 PDAB Airburst Cannon

Current Project: Bolt action rifle (25x140mm + 1in shot)

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Unread postAuthor: Gippeto » Fri Oct 17, 2008 12:41 am

Ken, 6061-T6 has an ultimate tensile strength of at least 42 000 psi, and a yield strength of at least 35 000psi.(according to wikipedia)

Use this handy little calculator to answer your question. :)

http://www.engineersedge.com/calculator ... t_calc.htm

Download gaseq to get an idea of what pressures/temperatures you will need to handle. (Do I need to tell you to do this first? :wink: )

http://www.arcl02.dsl.pipex.com/
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Unread postAuthor: kenbo0422 » Fri Oct 17, 2008 5:13 am

Thank you! I've found all kinds of info on pipe tensile strength, etc., but never how to convert to pressure ratings. I've got enough 6061 to last me for years and a friend who works at the machine shop next to my workplace keeps letting me have a few scraps of all kinds of materials. I have 3in cube blocks of nylon, steel rods, aluminum plate, 3/4 x 3 al bars, al blocks, SS rods and drill rod, etc., etc., etc. This could get interesting. I have a mini lathe that I got lined up (finally) and a mini mill for some small work, so now all I have to do is put my ideas into drawings and give them a try.

:D
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Unread postAuthor: Gippeto » Fri Oct 17, 2008 8:22 am

Ken, you are heading for interesting times indeed! :D
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Unread postAuthor: Ragnarok » Fri Oct 17, 2008 9:10 am

kenbo0422 wrote:I've found all kinds of info on pipe tensile strength, etc., but never how to convert to pressure ratings.

Bear in mind, it gives a yield pressure - this is not a pressure rating.

You do not want to get near this yield pressure - so really, you don't want to be going much above a third of whatever number you get.
Half at most, and that would be for a remote fire cannon.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: kenbo0422 » Fri Oct 17, 2008 11:49 am

You do not want to get near this yield pressure - so really, you don't want to be going much above a third of whatever number you get.
Half at most, and that would be for a remote fire cannon.


I'll be sure to keep that in mind. Oh, and the engineering calculator that I was referred to is now an excel file on my computer. Works well, and I experimented and found that the max pressure that McMaster puts on their PVC is usually rated at around a safety factor of 4.5. It also looks like relatively thin walled steel should be ideal for strength and weight even with safety factors of 8 and 7. (i.e.- 2.875" with .065 wall) Gives me hope, at least that I won't be spending a fortune on heavy gage steel pipe.
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