SOLUTION: I am a pipe fitter. I have been told a shorcut to determine an answer all my life and I cannot find out why it works I just know it does. And i'd like to know the formula way to ge

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Question 911990: I am a pipe fitter. I have been told a shorcut to determine an answer all my life and I cannot find out why it works I just know it does. And i'd like to know the formula way to get the answer. I will describe it in the way it effects myself. Take two pieces of metal and roll them into a cylinder. You now have two pieces of pipe pretty much. However since they was hand made it's never perfect. But we have two concentric circles that have to go together as even as possible. I will put a tape measure on pipe A and the circumference is 10 feet. I put a tape measure around pipe B and the circumference is 10 feet and 3/8 inches. I want to put them together with them being concentric. So I need the larger one to extend past the smaller one an even amount all the way around the circumference. I was taught to take Pipe B and subtract pipe A which would be (10'3/8") - (10') The answer would be 3/8". Then I would take the 3/8" and divide by 6 and the answer would be 1/16". doing that method I would leave the larger pipe B extending past pipe A 1/16" all the way around and it would come out perfect every time. I have done this for years and it works no matter the size or difference, you just subtract and divide by 6 and that's the difference. I am curious as to why? It must be a difference in the radi. But If you could tell me how I would find that answer not using the method I was taught. And if possible could you tell me why they use 6? I have asked before and the only answer I get is because it works. Thanks in advanced.
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
An explanation I can give is
The circumference is pi * D
where pi is a constant = 3.14
you are actually measuring the circumference pi * D1 & pi*D2 with measuring tape
where D1 is the diameter of the outer pipe
and D2 the inner pipe.
what ever are the sizes of the pipes the difference is a multiple of pi.
when you are dividing by 6
you are approximately dividing by 3.14 *2 or 6
when you divide by 6 you get the gap between the pipes.