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Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: TurboSuper » Sun Oct 19, 2008 10:38 am

Gippeto wrote:
TurboSuper wrote:Any metal pipe in 4" dia, be it copper, steel, or aluminium, is going to cost a bloody fortune.


I've been pricing out 4" pipe lately. :wink:

Even low grade steel has a tensile strength of 50 000psi +. (yes, I know that's not a burst rating, rough calculated burst pressure is around 1300psi)

I have found that 4" auger tube can be had for $6/foot.

4" galvanized exhaust pipe costs $10/foot.

Am I out to lunch thinking that is reasonable?


No, I'm just going by the prices I see around here: $50 for a 3" fitting. Youch,
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Unread postAuthor: Gippeto » Sun Oct 19, 2008 12:07 pm

D_Hall wrote:
Gippeto wrote:Even low grade steel has a tensile strength of 50 000psi +.

"Mild steel" is typically A36 or very similar. It's called "A36" because it has a tensile strength of 36,000 psi. A42 is also referred to as mild steel from time to time (42,000 psi tensile, of course). But to get up to 50 ksi you're starting to get into steels that shouldn't be classified as "low grade."


I didn't know that. Thanks for the tip!:salute:

I got my info from here; (some time ago, and I should have looked it up again before posting. :oops: )

http://www.boltdepot.com/fastener-infor ... Chart.aspx

I always figured that grade 2 (aka. garbage grade) was the low end for steel strength wise. I guess that I now know better. :)


Turbo, yeah $50 is pretty steep. I'm leaning toward a BigEd/Toolies inspired design, where everything is self fabricated and more cost effective.(cheap!)
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Unread postAuthor: D_Hall » Sun Oct 19, 2008 12:27 pm

Gippeto wrote:I didn't know that. Thanks for the tip!:salute:

I got my info from here; (some time ago, and I should have looked it up again before posting. :oops: )

http://www.boltdepot.com/fastener-infor ... Chart.aspx

I always figured that grade 2 (aka. garbage grade) was the low end for steel strength wise. I guess that I now know better. :)


Found a nice little graphic on McMaster that might be of use. It's just a quick-look chart showing different steel alloys and their yield strengths (note: things like Tool Steel may go all the way up to 140,000 psi).

Image

As for the bolts (where you got your numbers).... One thing to remember is that nobody wants a bolt that bends (makes it hard to screw in, ya know?). In addition, the parts are physically small. Those two things combined mean that manufacturers can use heat treatment (and quenching) to make the bolts stronger than they would "normally" be.

On the other end of the spectrum, people like to bend pipe and such so hardening isn't necessarily a good thing (remember: harder also means more brittle). And so they don't heat treat/quench.

Or even for parts that don't get bent a lot (say, I-beams), welding will likely destroy any heat treatment so there's just no point in doing it.
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Unread postAuthor: Gippeto » Mon Oct 20, 2008 12:26 am

One thing to remember is that nobody wants a bolt that bends (makes it hard to screw in, ya know?).

This is why we have BIGGER hammers! :lol:

Thanks for the chart, saved it to my reference file.
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