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Unread postAuthor: Ragnarok » Thu Dec 16, 2010 11:55 am

Fnord wrote:What's with the lack of builds coming in lately?

Snow and freezing/near freezing conditions across much of the northern hemisphere would seem to be a big factor contributing to this in recent weeks.
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Unread postAuthor: Fnord » Thu Dec 16, 2010 12:07 pm

I know winter slows things down, but really I haven't noticed a whole lot before that either. The combustion showcase still has stuff from May out in front.

Pneumatics are better off though still a lot of those are bump-ups.
BBMGs are impossible to judge given that's where JSR posts stuff
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Unread postAuthor: inonickname » Thu Dec 16, 2010 12:10 pm

Tech, that's a fair call....Now lets say you want to contain an atomic bomb detonation to make a nuclear powered space cannon. Lets say you have materials with a very fair absolute tensile strength of 150,000 psi. So for a even remote safety margin, you can have a differential of 50,000 psi between each layer.

Now, you need to hold back 20580000000 psi. Let's assume double that to allow for a working margin and unforeseen error. That's 41160000000 psi.

Ok, so with a differential of 50,000 psi per layer that is 823200 layers. You need to make 823200 layers and then individually pressurize each once in increments of 50,000 psi to reach a pressure high enough to hold the blast. If you can't see the logistical problems, you should contemplate suicide.

Lets pretend you can make 823200 layers, making each thick enough to withstand the 50,000 psi differential. You're already enclosing a nuclear device nearly a meter in diameter, how big do you expect it to be with 823200 extra walls each thick enough to withstand 50,000 psi? Not only that, how do you plan to reach 41160000000 psi in the highest layer? Considering it needs to be held there continuously.

Alright, lets pretend you've made this stupid device to contain a 41160000000 psi nuclear explosion. Will it work? No, of course it wont. You're exceeding the maximum pressure the material can feasibly hold by a factor of 274400. With a shockwave that is travelling at many times the materials speed of sound travelling through it, there is no way in hell it will survive. It will stop behaving as it usually would. You can see this even with conventional explosives. You can take a piece of plutonium and place it in the most powerful press you can find, braced to prevent expansion. You won't make it denser. However an array of shaped charges will easily compress the plutonium- enough for it to reach criticality and cause an extremely fast chain reaction.

When you have forces in play producing shockwaves that powerful, it's simply beyond the material full stop. Making some cute layers and filling them up with gas won't work around that. There is no work around. I expect the chamber to fail eventually, and will be taking precautions to make sure it cannot do damage when it does. Notes will be taken, and I'll make a new one. Simple.
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Unread postAuthor: Selador » Thu Dec 16, 2010 12:24 pm

inonickname wrote:So for a even remote safety margin, you can have a differential of 50,000 psi between each layer.


If you made something with all these layers...

Wouldn't each layer have to be fully contained, and floating within it's outer layer, without touching, anywhere ? (To be effective in the way theorized here.)

If so, then how you gonna get a barrel in there, to the innermost chamber ?
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Unread postAuthor: ramses » Thu Dec 16, 2010 4:41 pm

All my references to your "200x hybrid mix" have been in quotes for a reason. :D

There is another issue with tech's proposition; the very inside would be at atmosphere until the nuke went off.

I don't quite see the problem of exceeding the material's yield strength in pressure. Yield is a unit of pressure, so by increasing the thickness, you would distribute these forces, right? Does there come a point where you start dealing with the compressive yield strength?

Thanks for the insight. I'll do some FEA stuff later if I'm bored later.
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Unread postAuthor: inonickname » Thu Dec 16, 2010 8:20 pm

Selador wrote:
inonickname wrote:So for a even remote safety margin, you can have a differential of 50,000 psi between each layer.


If you made something with all these layers...

Wouldn't each layer have to be fully contained, and floating within it's outer layer, without touching, anywhere ? (To be effective in the way theorized here.)

If so, then how you gonna get a barrel in there, to the innermost chamber ?


Exactly. The logistical problems are simply ridiculous.

Ultimate tensile strength is intensive and doesn't vary over different thicknesses of material. It's a physical limitation of the material, regardless how thickly you build it.
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Unread postAuthor: jackssmirkingrevenge » Fri Dec 17, 2010 1:03 am

Fnord wrote:What's with the lack of builds coming in lately? It seems like JSR is running the forum by himself anymore. A quick glance at the showcases and it looks like a good bit of the front-page submissions are old bump-ups.
Back when I first joined it seems like there was a steady flow of stuff showing up; and a fair amount was actually pretty good.


Spudding is a fairly transient hobby for most people. Personally, I can't find anything else satisfying, if it's not something that blows deep/wide holes in stuff then I can't find the motivation to make it. Also, I can't bear the thought of not having something on the workbench or drawing board, of consuming and not creating. That's what keeps me going in a nutshell, but not everyone has the same priorities.
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Unread postAuthor: ilovefire » Fri Dec 17, 2010 1:21 am

jackssmirkingrevenge wrote:
Fnord wrote:What's with the lack of builds coming in lately? It seems like JSR is running the forum by himself anymore. A quick glance at the showcases and it looks like a good bit of the front-page submissions are old bump-ups.
Back when I first joined it seems like there was a steady flow of stuff showing up; and a fair amount was actually pretty good.


Spudding is a fairly transient hobby for most people. Personally, I can't find anything else satisfying, if it's not something that blows deep/wide holes in stuff then I can't find the motivation to make it. Also, I can't bear the thought of not having something on the workbench or drawing board, of consuming and not creating. That's what keeps me going in a nutshell, but not everyone has the same priorities.


that is EXACTLY why i am doing this hobby, i mean if i could find something that i liked doing just as much i wouldnt hesitate to switch, but whenever i look at a pice of pipe i think, barrel or chamber? would be good change because it wouldnt ba as illegal, plus not everyone would think im completely crazy
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Unread postAuthor: Gippeto » Fri Dec 17, 2010 2:02 am

I find myself more into building airguns than spudguns of late...fine line I suppose, but it's there.

Don't have any time for testing...daylight, non working hours are spent working on the house (getting near).

Build time is restricted to coffee and lunch breaks. Design time is evenings. As it sits, I've a heavily modded Qb 78 ready for "outdoor" testing, a Qb79 based field target rig nearing completion, a scratch built pcp that needs testing and tuning, and another big bore at the design/parts ordering stage.

And I've been tossing around ideas for my own version of the shoebox compressor. :wink:

Plenty going on...just no spuddys.
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Unread postAuthor: MrCrowley » Fri Dec 17, 2010 2:12 am

I think I'm most active in winter when things have picked up around here though of late I haven't been in the garage for awhile. Now that my piston hybrid is working well, I don't have a need to build anything else. I've got a bunch of fun pneumatics for shooting soda cans/golf balls/tennis balls/paint balls and the hybrid fulfills my power requirements. I doubt I'll build anything more powerful let alone have a reason to.

Don't have any plans for new cannons, haven't had any since I built the hybrid. Being a student and all, I don't feel like spending what cash I have on smaller projects to pass time.
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Unread postAuthor: Selador » Fri Dec 17, 2010 2:56 am

Gippeto wrote:And I've been tossing around ideas for my own version of the shoebox compressor. :wink:


Ok.

Dish.

:)
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Unread postAuthor: velocity3x » Fri Dec 17, 2010 1:36 pm

I always wondered what was inside my arm. I discovered that it just contains more arm. Be careful when in your shop. This is what sheet metal can do.
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Unread postAuthor: Selador » Fri Dec 17, 2010 3:14 pm

velocity3x wrote:I always wondered what was inside my arm. I discovered that it just contains more arm. Be careful when in your shop. This is what sheet metal can do.


Man, I had to block that image.

It was giving me the heebie jeebies.
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Unread postAuthor: Ragnarok » Fri Dec 17, 2010 3:16 pm

That's what superglue's for!
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Unread postAuthor: Lockednloaded » Fri Dec 17, 2010 3:25 pm

The dying off of new projects is mainly due to a lack of innovation IMHO. Way back when, piston valves , hybrids, and semi/full-automatic guns were just being developed, which stirred intrest in building new projects. As of now, there's some innovation going on, but nothing as revolutionary as past spudgun inventions.

just my .02...
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