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Short question topic

A place to ask general spud cannon related questions.
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Unread postAuthor: Goats spudz » Mon May 07, 2012 8:04 am

Hey wyz if you use that barrel you need to be carefull or sleeve it as its only thin tube and if you bang it it wil deform or bend.
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Unread postAuthor: warhead052 » Mon May 07, 2012 11:06 am

Goats spudz wrote:Hey wyz if you use that barrel you need to be carefull or sleeve it as its only thin tube and if you bang it it wil deform or bend.


I would hope he wouldn't bang it....
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Unread postAuthor: wyz2285 » Mon May 07, 2012 11:16 am

Do you think I´m stupid enough to bang it? I would have stainless steel cover for it if I´m going to use it on my pcp.
After GGDT a lot, I´m seriously thinking about buy the LW .177 barrel, .22 does give me about 10J more energy, but I´d prefer the .177´s high muzzle velocity (estimate >300m/s for a light pellet).
Hope it does worth the price :?
Have is a question: that´s the difference between these two?
.177 Cal 16mm dia X 605mm long with choke
;
.177 Cal 16mm dia X 605mm long, Polygon Rifling With Choke
One is rifled? But for that price I´d assume they all are rifled barrel...
also very strong :roll: no?
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: Gippeto » Mon May 07, 2012 11:45 am

Be aware that the LW blank is just that...it will need to be chambered for the pellet, a leade cut into the rifling, any transfer ports done, these deburred and crowned.

It'll also need to be blued as they come "in the white".

Polygonal barrels have a reputation for being pellet fussy.

The Crosman barrel is 7/16" od, and isn't made of spaghetti...it's steel. Not as fragile as some would think. It also comes ready to use...which may be a deciding factor if you lack machining facilities.
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Unread postAuthor: wyz2285 » Mon May 07, 2012 12:26 pm

lack machining facilities.

Don´t worry, I have this part well solved :D
I will buy the corssman barrel anyway, for a pump action or pcp, it will be machine as well.
just thinking SHOULD I buy the .177 LW barrel to make a really good pcp, as I already prepared everything and spend a lot of time on design.
Can you be more detailed, please :P I really have no idea how to blue anything, also how to/what to do the chambering :oops:
Also I have finished designing my pcp, still not final, but I like it.
My question is, the pressure I will be using is 200 bar in the main chamber, 120 bar after the regulator, how deep/length should the threads be?
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: Gippeto » Mon May 07, 2012 1:44 pm

Four feet of class 3b FTW threads might work. :roll:

Are you SURE you're up to this?

You ask "how deep/length should the threads be" without providing the information that is required for someone to properly answer your question...You are demonstrating a total lack of knowledge on the subject, which is not good IMO. I'm thinking you need to do some homework on this.

200bar might not seem like much when you're merely looking at a number....but it CAN and WILL kill you if you give it a chance.

Please...DO the homework first...then we'll talk.

As far as your design goes...my own personal preference would be to have the o-rings positioned to isolate the threaded sections from pressure. When you've done your homework you'll be able to tell me why that is. And maybe a reason or two why manufacturers do it the same way you want to. :wink:

Do some research on "thread class", "thread shear", "barlow's formula" and "yield strength".

There are several ways to blue steel...cold blue is the easiest, most widely available type...and the least satisfactory. The other options involve nasty chemicals and high temperatures....have not investigated slow rust bluing sufficiently to comment on it.

Chambering is done on the lathe. Best done with a specially made chambering reamer. (You can make a suitable one from oil hardening rod.) Have read about some folks chambering a barrel using drill bits...not sure how that would turn out, but keep in mind that the barrel will only shoot as good as the weakest part...sloppy machining will NOT make the grade.
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Unread postAuthor: Gun Freak » Mon May 07, 2012 6:32 pm

Wyz, if it we me, I'd go with the cheaper barrel. In a homemade gun I honestly don't think you'll notice a difference between the cheaper one and the really high quality one that Gippeto praises.
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Unread postAuthor: DYI » Mon May 07, 2012 6:42 pm

Wyz, you really should at the very least know enough about solid mechanics to get a general idea of the wall thicknesses and thread engagements required, and an understanding of how to avoid stress concentrators as much as is possible (and why you want to avoid them).

For building a handheld high pressure pneumatic, I suggest going one step further - learn to use an FEM program (RJB will have access to one) to take out the guesswork entirely. You'll end up with a much more lightweight launcher if you can predict more closely what the stresses will be.

If you're looking for learning material, there are loads of MIT lectures posted online, which are free to access. You should have no trouble getting an entire solid mechanics course (or three) from there. Alternatively, there are loads of useful texts available on Scribd and 4shared.
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Unread postAuthor: wyz2285 » Tue May 08, 2012 4:29 am

I know I'm going too fast, but I don't have much choice, I need to have the blueprint of all the parts ready before July. I knew I don't know enough as soon as they asked me what type of material I want the parts made of, I said stainless steel, then they asked witch type of stainless steel, I wasn't capable of answer.
But, the parts will be made by very experienced factory workers on high end machinerys.
I will do the readings, then let's see if I can get better.
I got a student version of inventor fusion 2013, but haven't find out how to use it to calculate material stress yet...
The reason why I want a good barrel is, with a straight 6mm aluminium barrel I´m able to have a groupo of 5cm dia at 25m, with homemade guns. As these guns I´m designing right now will be factory made, I want them to be better than homemade ones, like a 1cm grouping in the same distance.
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: wyz2285 » Tue May 08, 2012 11:20 am

I read this for "thread class", witch made me thinking about class 2 threads, I don´t want snug fit, I want the gun to be easy to assemble/disassemble;
For "thread shear" I only found formulas/calculators, but I got the idea, it´s the area of the threads where stress are applied.
Found http://en.wikipedia.org/wiki/Barlow's_formula for "barlow´s formula", and this is a question I forgot to ask. Originally I thought about 3cm ID and 4cm OD stainless steel chamber(witch type of stainless? I don´t know either :oops: ).
Studding http://en.wikipedia.org/wiki/Yield_(engineering)yield strength right now, already have a basic idea about it.[/url]
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Unread postAuthor: Lockednloaded » Wed May 09, 2012 6:00 pm

I'm thinking of making a shell for a paintball gun projects I'm working on, but I don't want it to permanent, because I need the thing to be serviceable. So I'm asking anyone who has used bondo before; could I cast the bondo around the gun in two parts to make a shell? If so, would I need some sort of cast releasing spray to make sure the stuff doesn't stick?
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Unread postAuthor: Gippeto » Thu May 10, 2012 1:10 am

Bondo IS sticky...use a release agent. Try it out on something of no consequence first. :wink:
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Unread postAuthor: jackssmirkingrevenge » Thu May 10, 2012 1:37 am

If you want to make a shell it makes more sense to do something like this:

http://zoneballistic.com/colinsballisti ... glass.html

You could also carve a foam shell and cover it in fibreglass.
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Unread postAuthor: Goats spudz » Fri May 11, 2012 11:05 am

Does anybody know the specifications on a paintball ASA thread, i need to screw cut some adapters for a paintball regulator.
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Unread postAuthor: jackssmirkingrevenge » Fri May 11, 2012 11:10 am

1/2" BSP fits it.
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