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Interrupted Screw

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Interrupted Screw

Unread postAuthor: thunderskunk » Sat Jun 21, 2014 11:59 pm

Evenin folks

So I had a change of heart. I can't get my ignition to work in the shells I've been trying to get my howitzer to fire, so I'm giving up on using a precharged shell altogether. Now it's just a shell with a potato shoved up the chamber, and a screw on backing to my 4 inch chamber like every other spud gun in the world.

Here's somethin though. My door action won't be any good with a screw-in breech plug. SO, what about an interrupted screw?

Well, I decided to experiment, and came up with something that... worked but didn't work.

SUNP0146.JPG

SUNP0147.JPG


The mechanism worked. But, it did leak quite a bit. on this little tiny version, that wouldn't be a problem because I have a rubber gasket that solves the issue. My larger version doesn't have the shelf for a gasket, so shaving the threads would leave a pretty big gap.

So, lemme know what you think to these possible solutions:

-Leaving one thread at the end of the cap for a seal

-Screwing a plate to the back of the cap with a rubber gasket

-saying screw it... as in not use an interrupted screw because these parts were ten bucks and I'm a cheap SOB.

Oh, and I painted it. Here's the updated pics:

SUNP0141.JPG

SUNP0142.JPG

SUNP0144.JPG
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Re: Interrupted Screw

Unread postAuthor: jrrdw » Sun Jun 22, 2014 5:52 am

O-rings (2 of them) at the end of the breach. At 1/4" and 1/2" from the breach opening. Mount them on the plug for easy access and replacement when needed.
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Re: Interrupted Screw

Unread postAuthor: thunderskunk » Sun Jun 22, 2014 8:32 pm

Haha, you called it. I needed three rings and a pad. I needed to make them myself, but they worked in the end.
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Re: Interrupted Screw

Unread postAuthor: jimmy101 » Wed Jun 25, 2014 6:38 pm

You mod'd a cleanout plug? That's the weakest part (almost certainly not a pressure rated part) in the gun. Plus, I would suspect that cleanout's are tapered (like pipe threads) or have a slightly variable pitch to help them seal. Be a good idea to not stand behind the breach when firing.

BTW, the cannon looks great.
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Re: Interrupted Screw

Unread postAuthor: thunderskunk » Thu Jul 03, 2014 9:55 pm

Just in case someone looks at this and wants to do the same thing:

I've fired the gun on several occasions now. My shells work awesome, and the threads still exist on my chamber door, which is a good sign. A few notes, you 100% need a gasket, and the way you make it can either work for or against you. I'll post pictures here in a bit, but the threads will only hold the door "tight" at a certain angle. You can adjust that angle by adding more or different thicknesses of rubber gaskets to the door, as long as they fit properly.

Another note, up until today I haven't gotten my door to hold a seal for more than one shot. The whole point of the interrupted screw is to make reloading the gun faster. If you don't have the need or means to rapid-fire your gun, stick with the threads. It's safer and much more sure-fire.

BUT! Now that the door does hold a seal, we were able to make a science out of the operation and fired three rounds in a little over a minute, and hit the same target (generally...). So if you can make it work, the rewards are great
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