Creating Ellipses in Pottery ```Name: Mark S. Status: Student Age: 30s Location: N/A Country: N/A Date: May 2003 ``` Question: I am an art student and need help with a geometry issue. I am making teapots which are oval so the openings are ellipses. I need to create lids which are also then reshaped as ellipses to fit. What I need to figure out is with a given ellipse is there a way to determine it's circumference to use as a guide for creating the same circumference of a circle lid? The idea is that I use a wheel to throw the lids which makes them round then I compress them a bit to reshape them oval. It seems like as long as the two circumferences match they will fit? Replies: According to "http://home.att.net/~numericana/answer/ellipse.htm", there is no exact solution in closed form, but this approximation is very good: PI * (3*(a+b) - sqrt((3*a+b)*(a+3*b))) where 2*a is the length of the major axis (the largest measurement through the center) and 2*b is the length of the minor axis (the smallest measurement through the center). Tim Mooney The perimeter,P, of an ellipse that has a major axis, the long way, equal to: 2A, and a minor axis, the short way, equal to 2B is approximately: pi*(2(A^2 +B^2))^1/2 where pi = 3.14... And this is an approximation. The exact analytical answer is much more messy algebraically. I am not sure this is going to be of much practical value. I have another suggestion of how you might approach the problem. A company, Alto Inc., sells supplies for matting photographs, art work, etc. They make elliptical templates that you could cut out of matting board, or cardboard, or some other "cut-able" material, and you could use the templates to serve as a guide for matching the pots and their lids. Cost is ~\$60. Their e-mail is: www.altosezmats.com and phone number: 1-800-225-2497. I do not do pottery, but this seems like a more practical and simpler solution. Since you could save the template(s), all the tea pots could be the same shape. Vince Calder Click here to return to the Engineering Archives

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