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Thread questions

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: btrettel » Mon Jan 05, 2009 6:49 pm

I recently decided to buy a small low pressure aluminum cylinder. The threads on the cylinder are a little odd--they are straight, 1 inch diameter, 14 threads per inch, and have a 60 degree thread angle. This is not part of the usual "Unified Thread System" so I thought it was a problem, initially at least.

Later I remembered about NPT fittings. 3/4 inch NPT threaded fittings are 1.050 inches in diameter, have 14 threads per inch, and have a 60 degree thread angle. The diameter is a little too big at the top, but NPT fittings are tapered, so I'm thinking it'll fit and seal with some teflon tape.

Does this sound reasonable? I guess the only way to know for sure is to test it and see but I'm thinking others might have some relevant experience. If not, then someone else might find this information useful.
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Unread postAuthor: frankrede » Mon Jan 05, 2009 6:53 pm

They should be compatible, if I were you I would contact the manufacturer.
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Unread postAuthor: btrettel » Mon Jan 05, 2009 7:01 pm

I had to contact them to see if it was in my price range. They said they can do a variety of threads, so I asked about NPT threads. The person I was speaking to didn't have a clue what I was talking about. They probably were just a peon and didn't know their company's actual capabilities. I'm betting this size was chosen because it is similar to 3/4 inch NPT, but I can't know for sure. I'll be sure to ask when ordering.
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Unread postAuthor: btrettel » Tue Feb 10, 2009 7:45 am

An update: I spoke to a more knowledgeable person at Catalina Cylinders and I could probably get the thread to work with 3/4 inch NPT threads, but it'd likely damage the cylinder in the process.

However, they do sell a bushing called F1 that goes from their odd threads to 1/4" NPT female. I'm going that route.

I'd also like to comment that Catalina Cylinders is a great company overall and they'll go out of their way to help you. I highly recommend them.

Edit: I received the pressure vessel today. It's nearly perfect for my application and I'd suggest Catalina Cylinders if you want a lightweight and relatively cheap repeater without using HPA.
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