Hi All,
Anyone have experience or idea in modeling turbin francis in Rhino and with Grasshoppper, please comment at here
for example image
Thanks
use a spiral with one turn with 2 different dimension. you may have to adjust the tangency of the spiral hitting the straight curve, either manually or you join the curves and use rebuild with something like 14-15 points or you use the plugin or pyhton script found in this thread, OR you can also use BlendCrv you can also trim parts from both curves off to get a bigger transition first and then BlendCrv. after that use pipe with 2 different dimension.
here a crude quick example.
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Thank you so much,
can you help me by one short video 
hehe, i could, but its a bit of a fiddling around till i get it to look like you want and will not be a smooth video, or will look like a mess, and since a flue is tridenting me you may have to wait a day or 2.
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Generally the design of a volute casing would involve laying out cross sections that have uniformly decreasing area around a center circle.
This file shows one possible technique
turbo.3dm (207.7 KB)
The steps would be to loft the start and end shape of the volute, Then extract evenly spaced cross sections using contour command and arrange those sections around a circle and then loft.
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