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2.4kpsi helium powered BB gun - build log

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: SpudBlaster15 » Sat Jan 19, 2008 7:22 pm

I kinda figured that the machining costs would be absurdly high. Too bad.

Just wondering, what modifications do you intend to add to the SCTBDC?
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Unread postAuthor: ALIHISGREAT » Sat Jan 19, 2008 7:29 pm

awww i was really looking foreward to seening it in action... ahh well i'm sure someone else will try a 2.4kpsi helium bb gun... oh wait *sigh* theres no one excluding DYI crazy enough to take on this project :cry:
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Unread postAuthor: socoj2 » Sat Jan 19, 2008 7:30 pm

DYI wrote:Update:


The steel bar stock I obtained is too hard to be properly machined with any bit. The quote I obtained from a machine shop for building the valve was, well... :cry:


A. Have you tried to get aluminum?
b. Dont know what you need machines, but you might want to look into a combination of A flow Jet shop and a machine shop.

I recently gota quote from a machine shop to make some brackets out of 1" aluminum, and they wanted $600+ materials. Flow jet shop was $75 BYOMetal I had them cut the brackets and then brought them to the machine shop to have the holes tapped. Went from $600+ to $115
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Unread postAuthor: Hawkeye » Sat Jan 19, 2008 7:32 pm

Are you sure you didn't order a PW handle that is deliberately designed to leak slightly?
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Unread postAuthor: Novacastrian » Sat Jan 19, 2008 7:38 pm

Hawkeye wrote:Are you sure you didn't order a PW handle that is deliberately designed to leak slightly?


Now that is just cruel Hawkeye! I don't see why one would design a leaky PW handle.
My heart bleeds for you DYI- all that work to discover that the bloody thing "leaks like a sieve". I guess we live and learn.
I hope you figure out a solution soon- 2.4k sitting there doing nothing must be eating at you. :cry:
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Unread postAuthor: Isomer » Sat Jan 19, 2008 7:41 pm

ya, if the pressure washer handle was supposed to work at 2.4k psi and started to leak at 500, either it's broken (you would probably be able to send it back) or it's supposed to do that. About the machining, I have a le blond metal lathe in my garage and I can machine up to .0001" and im not suprised at the quote from the machine shop. Doin parts of that prescision is time consuming to say the least.
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Unread postAuthor: Novacastrian » Sat Jan 19, 2008 7:50 pm

Isomer wrote:ya, if the pressure washer handle was supposed to work at 2.4k psi and started to leak at 500, either it's broken (you would probably be able to send it back) or it's supposed to do that.


Wrong, it is designed with water in mind. Water is A lot denser than gases (think 10000 times denser). As such the PW handle would most likely seal under the conditions it was designed to be used for i.e. H20.

You may be onto something when you say DYI could send it back, maybe they would offer him store credit, i can't see them offering a full refund. Not unless it is faulty- which it most probably isn't.
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Unread postAuthor: Hawkeye » Sat Jan 19, 2008 8:13 pm

They design them to leak slightly when used in conditions where they may freeze without a slight flow through. At a car wash in a colder climate for example. You can google examples. I believe they call them "weeping".
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Unread postAuthor: DYI » Sat Jan 19, 2008 8:41 pm

Hmm.... Lots of responses here.

I haven't given up on the project. It will get done, just not immediately. As Nova stated, the washer handle was designed for water, not gases. I was a bit too optimistic with my assumption that it would seal at 2400 since it was rated for 4k. It will get done at some point, simply for the point of being able to say I've done it. I have a friend that might do the machining for cheap, whom I'll contact in the spring/summer.

As for the upgrade to the SCTBDC, the term "upgrade" may be a bit of an understatement. The planned upgrade will take place after the snow melts, and should cut the size in half, while maintaining the same power and cutting operating costs to less than 5% of what they currently are, as well as cutting reloading times by roughly 50%, possibly much more.
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Unread postAuthor: Novacastrian » Sun Jan 20, 2008 2:54 am

Hawkeye wrote:They design them to leak slightly when used in conditions where they may freeze without a slight flow through. At a car wash in a colder climate for example. You can google examples. I believe they call them "weeping".


Hmmm, i have learnt something new today. Thanks Hawkeye.
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Unread postAuthor: TurboSuper » Sun Jan 20, 2008 11:44 am

This seems like a cool idea; Just take a simple-ish design and make it work with insanely high pressures. I like :D
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Unread postAuthor: Gippeto » Sun Jan 20, 2008 5:49 pm

DYI, have you tried annealing the steel? I'm working with 1045 (medium carbon steel), and have to anneal each piece before machining on my tinker-toy of a lathe. Or you could try something like 1117 which is supposed to be free machining.

You might also consider sealing your end with a quad-ring and cross bolting with socket head cap screws, (if you have the room) around the circumference. This would eliminate a lot of the (paid for) machining. (ie. cutting threads on a lathe is a lot harder than drilling and tapping a hole)
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Unread postAuthor: DYI » Sun Jan 20, 2008 7:06 pm

There's a lot of machining to do, and holding the thing together with bolts would be rather nervewracking, as well as very inconvenient.

The bottom line is, you'll just have to wait a while to see this. I haven't given up on it, it's just fallen down a bit on the priority scale. When I do make it, it'll be .50 cal rather than .257, so it may just be worth the wait.
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