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Machined pengun - Dimply

Discuss miniature cannons built from things such as pill bottles and pen caps.
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Unread postAuthor: saefroch » Sat Aug 06, 2011 1:51 pm

jackssmirkingrevenge wrote:an idea in the shower combining balls and ring
Wait... I think I've heard this before... :wink:
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Unread postAuthor: POLAND_SPUD » Sat Aug 06, 2011 7:33 pm

@LeMaudit
I challenge you to design a lead sealed cartridge
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Unread postAuthor: LeMaudit » Sat Aug 06, 2011 9:52 pm

@LeMaudit I challenge you to design a lead sealed cartridge

I always love a good challenge... but...

lead sealed? :shock:
I was exited by a design for a seal made with o-ring, and at the same time positively locked, typically for a large ball bearing projectile.
:oops: I'm not sure to understand the challenge related to the previous messages! I only had in mind steel balls as projectile with this design, no lead bullets or pellets. :?
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Unread postAuthor: POLAND_SPUD » Sat Aug 06, 2011 10:10 pm

well let's face it... it would be cool if he could get rid of o-rings and use lead only

Ever heard of a process called swaging ? I think something like that might work...
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Unread postAuthor: LeMaudit » Sat Aug 06, 2011 10:31 pm

well let's face it... it would be cool if he could get rid of o-rings and use lead only


Right! Now I understand what you mean, sorry :D
But JSR already kinda made something work, sealing a pellet like that. Can't remember where... but it's somewhere...
For me... no way I would manipulate a small cylinder under pressure with a projectile that is not positively locked Image

I want to be able to drop the thing... and feel safe about it... cause I will drop the thing :?

The path I personally follow right now is more a way to make a large cartridge, vol. about 2 inch³, but without a projectile in it. My next experiments will be oriented to large bore / sabot and I see the cartridge as a quick reloading way for single shooter, not for semi or full auto.

Semi and full auto with cartridges are JSR Holy Grail, I'm too much a beginner to start with that! Only made a pengun so far :wink: But later, later...
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Unread postAuthor: POLAND_SPUD » Sat Aug 06, 2011 11:02 pm

no way I would manipulate a small cylinder under pressure with a projectile that is not positively locked
I don't think this is such a big deal with smallbore projectiles... cartridges have no barrel so the velocity shouldn't be high

Besides I think it is possible to design one that would be safe
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Unread postAuthor: LeMaudit » Sun Aug 07, 2011 7:43 am

I don't think this is such a big deal with smallbore projectiles...

Unlike JSR, I'm much more interested by big bore. The pengun was.. an accident :D A simple way to explain machining procedures with an example. But my main interest goes to big bore, .50 and more. For an interesting power, GGDT often gave me figures around 2inch³ volume or air, between 400 and 800 psi. That would mean a minimum size cartridge about 3/4" diameter, 5" long. I guess 1" OD-6" long would be closer to the reality with wall thickness and firing mechanism. That's... about the length of my pengun, twice the diameter :lol:


cartridges have no barrel so the velocity shouldn't be high

More than enough to shoot your eye out. Or someone else's.


Besides I think it is possible to design one that would be safe

If you have some ideas please share them!
I've searched for a long time one that was at the same time:

1- compact
2- positively locked
3-safe to manipulate
4- able to resist at least 400 psi, better 800 psi
5- air flow without restriction, close to the caliber section
6- fast opening time
7- refillable with a shock pump
8- minimum number of components to be able to build a quantity (10 or so)
9- minimal force applied to firing mechanism
10- simple to build (on a machinist point of view) and if possible using off-the-shelf components.

So far, I never found a design that have all those points.
2 and 3 means for me whatever fail (o-ring, shrader, assembly join) or happen like dropping the cartridge, catching a pin or pushing a ring, it will not fire.

A few days ago I found a way to maybe have 2,3,4,6,7,8,10. I plan to give it a try soon and show the result (in another discussion topic).
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 07, 2011 11:21 am

POLAND_SPUD wrote:Ever heard of a process called swaging ? I think something like that might work...


As LeMaudit pointed out I've already done this, both for pneumatics and hybrids (on your suggestion!) ;)

Here's my idea from yesterday, the ball detent holds an internal tube that keeps the o-ring compressed...
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Unread postAuthor: Gun Freak » Sun Aug 07, 2011 12:35 pm

I don't think that's a good idea... Doesn't seem fool proof enough to me.
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 07, 2011 1:40 pm

Gun Freak wrote:I don't think that's a good idea... Doesn't seem fool proof enough to me.


I'm pretty sure it could work, using an o-ring detent compressed by a threaded fitting it's possible the fire a blocked projectile by loosening the thread thus reducing the compression on the seal.

Still, too complex for my liking.
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Unread postAuthor: LeMaudit » Sun Aug 07, 2011 3:31 pm

jackssmirkingrevenge wrote:
Gun Freak wrote:I don't think that's a good idea... Doesn't seem fool proof enough to me.


I'm pretty sure it could work, using an o-ring detent compressed by a threaded fitting it's possible the fire a blocked projectile by loosening the thread thus reducing the compression on the seal.

Still, too complex for my liking.


It certainly could work, but it have not this 100% safe feeling I seek... for that reason it seem to me overly complex without any gain (... :shock: wow... now I can detect those kind on my own... I must be getting old and wise...)

Too much pressure, or a o-ring that crumble/tear-off will result in a projectile that shoot unexpectedly. With a positive lock in front of the projectile, as a brass ring or several small steel ball like a quick coupler, it will not.
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Unread postAuthor: LeMaudit » Sun Aug 07, 2011 9:36 pm

Here's my best try.

The rubber washer could be replaced by a o-ring... but I feel this will have more chances not to be ripped-off by the air flow

The UHMW ring could be replaced by a few small steel balls to limit friction, but it will then need additional design to keep everything aligned.. little grooves, etc... it's much more work in term of number of machining operations

The same design should work with many kind of projectiles, if they can seal pushing on the rubber under pressure. And I'm pretty sure I could make that design to fit any size, from lead pellet to airsoft to .50 lead bullet. The only difficulty could be to find a perfect sized rubber washer, but that could be mold in RTV rubber quite easily in quantity.

I'm quite happy with this one, it answer all my 10 points, except maybe the 9- minimal force applied to firing mechanism.
UHMW is quite slippery, it is used to do low speed bearings. So maybe not much force should be applied to slide the ring back. If not, small steel balls will need to be used.

What do you think guys? Anyone with experience on UHMW friction under pressure?
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