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Strength of Screws?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Strength of Screws?

Unread postAuthor: Velocity » Tue Jan 08, 2008 7:25 pm

For a coaxial that I will be attempting, I bought a few screws, but I am not sure if they will be strong enough. Here is the scenario. The chamber is a length of 1.25" OD aluminum tube, with an ID of 1.12" (wall thickness is .065"). The barrel has an OD of .75". For the front end of the coaxial, the barrel will fit through a small machined donut made of aluminum. This donut will have an ID of 1.12" to fit inside of the chamber, and an ID of .75" to allow the barrel to slip through.

The barrel will be secured by epoxy, welding, something like that; I am not really concerned about that. The donut, however, will be secured to the chamber with screws. The screws which I bought are 3/16" in length, with a thread size of <a href="http://www.engineersedge.com/screw_threads_chart.htm">5-40</a>. I will be placing several, probably in the vicinity of 10-12, around the outside of the aluminum pipe.

Should these be strong enough to hold the aluminum donut in place? Or should I upgrade to a larger screw, with a length of 1/4"? Sorry if my description is difficult to understand... I'll see about drawing up a picture....
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Unread postAuthor: cwazy1 » Tue Jan 08, 2008 7:27 pm

i always use number 12 screws for any pressure holding app.

also, keep in mind that in this app, more is not better, if you have too many, it could damage the strength.
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Unread postAuthor: dewey-1 » Tue Jan 08, 2008 7:36 pm

--
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Last edited by dewey-1 on Sun Apr 20, 2008 2:40 pm, edited 1 time in total.
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Unread postAuthor: Novacastrian » Tue Jan 08, 2008 7:53 pm

How about screwing said screw through something and actually testing it's shear strength? Divide the weight it can hold in two for a safety factor and you have some real numbers to work with.
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Unread postAuthor: potatoflinger » Tue Jan 08, 2008 9:29 pm

Why not weld it to the chamber the way you welded the barrel to the donut?
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Unread postAuthor: brogdenlaxmiddie » Tue Jan 08, 2008 9:42 pm

because, if its on the inside of a pipe, that would be rather difficult. But, you could use the epoxy AND the screws :idea:
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