Page 21 of 22

Re: preloaded pneumatic cartridge

Unread postPosted: Tue Feb 19, 2019 6:43 am
Author: jackssmirkingrevenge
Thank you gentlemen.

Gippeto, no powered feed on the Sherline so I'm restricted to taps and dies for cutting threads, which is the machining operation I dislike the most, so pinning it is :)

Now that this has some chance of working I've progressed to the next stage of planning being what sort of blowback mechanism would be best.

Image

"closed bolt" mechanism with a separate spring-loaded firing pin.

Image

"open bolt" mechanism with a floating firing pin.

I'm inclined towards the latter, it's easier to build, perhaps less accurate due to greater movement before firing but that is not really a concern for what is meant to be a plinker. It will also cycle on full auto as long as the trigger is pressed, the closed bolt would be more difficult to implement as a select fire device. Not that with a limited amount of cartridges that would last very long anyway.

Re: preloaded pneumatic cartridge

Unread postPosted: Fri Feb 22, 2019 10:34 am
Author: jackssmirkingrevenge
In the interest of adding to the catalogue of existing technology, here is the APS APM cartridge for the APM50 rifle:

Image

Note that this is the "Angel" low power version, which is why the air chamber is so small relative to the cartridge body. The firing and filling cycles are shown.

You can see that the concept is virtually identical to the MAC cartridges, indeed it might have been the inspiration as it predates Inovairtech's products.

Image

I've been thinking about simplifying the design in the interest of easier manufacture, since I'll be wanting to make a few of these.

Here is my current thought, with one o-ring at each end simultaneously sealing the piston and the chamber, sandwiched with delrin washers pushed by a single spring:

Image

Re: preloaded pneumatic cartridge

Unread postPosted: Fri Feb 22, 2019 10:45 am
Author: hectmarr
Very interesting, and a class of this technology for which we do not know everything. I'm going to try some of these cartridges. I like them a lot and it's a matter of looking for the form without needing complex machines.
I've thought about doing something like that. It is quite simple to build.
The central duct of the air tank, is to level the pressure on both sides of the moving air chamber. It is to prevent it from closing itself by increasing the pressure on the left side where the ammunition is.
To recharge the cartridge with air, the accessory that introduces the compressed air must be screwed into the tip, tighten the firing pin and let the air pass. Once the pressure is programmed, the rod is released and the spring seals the outlets of the air chamber.
It should be very simple to open because the pressures are balanced. forever.

Re: preloaded pneumatic cartridge

Unread postPosted: Sun Feb 24, 2019 12:18 am
Author: hectmarr
I tried an animation, we'll see if it comes out correctly :?

Re: preloaded pneumatic cartridge

Unread postPosted: Sun Feb 24, 2019 4:17 am
Author: jackssmirkingrevenge
Interesting, my only concern is that since the o-rings have a large diameter, even though they are balanced there will be considerable friction at higher pressures so a larger force will be needed to actuate the cartridge.

Re: preloaded pneumatic cartridge

Unread postPosted: Sun Feb 24, 2019 8:11 am
Author: hectmarr
jackssmirkingrevenge wrote:Interesting, my only concern is that since the o-rings have a large diameter, even though they are balanced there will be considerable friction at higher pressures so a larger force will be needed to actuate the cartridge.

Yes, it is probably as you say. I thought about using it at about 15 bar which is the most I can compress. Only in those conditions does it seem to me that it can work.

Re: preloaded pneumatic cartridge

Unread postPosted: Sun Feb 24, 2019 1:40 pm
Author: keks2033
hectmarr wrote:
jackssmirkingrevenge wrote:Interesting, my only concern is that since the o-rings have a large diameter, even though they are balanced there will be considerable friction at higher pressures so a larger force will be needed to actuate the cartridge.

Yes, it is probably as you say. I thought about using it at about 15 bar which is the most I can compress. Only in those conditions does it seem to me that it can work.

It will work very badly. When the hole passes over the sealing ring, the pressure will again move the cylinder with air back, all the air will not have time to get out. Better make a pneumatic cartridge with a piston valve, it is easier and 100% working.

Re: preloaded pneumatic cartridge

Unread postPosted: Sun Feb 24, 2019 1:48 pm
Author: hectmarr
keks2033 wrote:
hectmarr wrote:
jackssmirkingrevenge wrote:Interesting, my only concern is that since the o-rings have a large diameter, even though they are balanced there will be considerable friction at higher pressures so a larger force will be needed to actuate the cartridge.

Yes, it is probably as you say. I thought about using it at about 15 bar which is the most I can compress. Only in those conditions does it seem to me that it can work.

It will work very badly. When the hole passes over the sealing ring, the pressure will again move the cylinder with air back, all the air will not have time to get out. Better make a pneumatic cartridge with a piston valve, it is easier and 100% working.

The central duct levels the pressure on both sides of the mobile air chamber.
To work at a moderate pressure can work.

Re: preloaded pneumatic cartridge

Unread postPosted: Sun Feb 24, 2019 4:06 pm
Author: keks2033
hectmarr wrote:
jackssmirkingrevenge wrote:Interesting, my only concern is that since the o-rings have a large diameter, even though they are balanced there will be considerable friction at higher pressures so a larger force will be needed to actuate the cartridge.

Yes, it is probably as you say. I thought about using it at about 15 bar which is the most I can compress. Only in those conditions does it seem to me that it can work.

Try to make it better. At high pressure, it can break, but at low it should work well and for a long time.

Re: preloaded pneumatic cartridge

Unread postPosted: Sun Feb 24, 2019 7:18 pm
Author: hectmarr
keks2033 wrote:
hectmarr wrote:
jackssmirkingrevenge wrote:Interesting, my only concern is that since the o-rings have a large diameter, even though they are balanced there will be considerable friction at higher pressures so a larger force will be needed to actuate the cartridge.

Yes, it is probably as you say. I thought about using it at about 15 bar which is the most I can compress. Only in those conditions does it seem to me that it can work.

Try to make it better. At high pressure, it can break, but at low it should work well and for a long time.

I'm trying to understand your diagram.

Re: preloaded pneumatic cartridge

Unread postPosted: Sun Feb 24, 2019 8:06 pm
Author: hectmarr
Maybe in this way it is not very hard to open. What I need is for it to be very simple to build. It is the same but with small o`ring.

Re: preloaded pneumatic cartridge

Unread postPosted: Mon Feb 25, 2019 4:17 am
Author: jackssmirkingrevenge
hectmarr wrote:I'm trying to understand your diagram.


Here it is animated, the system is balanced at first, until the stepped piston is exposed letting the pressure pull it back:

Image

Here is another variation where the pressure blows the piston forward:

Image

Re: preloaded pneumatic cartridge

Unread postPosted: Mon Feb 25, 2019 11:37 am
Author: hectmarr
This is the way to build the rudimentary little air cartridge. I need three tubes of different sizes, a three o`ring metal shaft and resin,and a small spring.
What is yellow, are the locks to reinforce the resin caps fixed to the tubes. In the small tube with the holes for air to escape, I will use small bolts to make room with the outer tube.
I'm looking at the size depending on the pressure I can make with my modified fridge compressor, a 200 psi.
On the front, a threaded part of those used in domestic, bronze gas connections is glued and secured.
It is to shoot bb`s of 1/4 "steel. :shock:

Re: preloaded pneumatic cartridge

Unread postPosted: Tue Feb 26, 2019 7:53 am
Author: jackssmirkingrevenge
What is the purpose of the inner chamber in your design? It seems like an unnecessary complication when it's the spool that's doing all the work, if I understood it correctly.

Re: preloaded pneumatic cartridge

Unread postPosted: Tue Feb 26, 2019 8:40 am
Author: hectmarr
It's just to make construction possible for me. It is necessary to have a station between the outer casing and the air chamber, through which the air can pass from the back to the front of the cartridge, and it is for this reason that I thought it could be like that. The small air chamber should not move.
Another possibility can be this, within the basic and very simple to build. At first glance it could work ...