Hi Peter. Well. Obviously it's not perfect. The sweep is still a polysurface. In Rhino in fact i have a method which is simpler than Moi and will generate it as a single curve segment, so the resulting pipe (thickening the curve) will result in a single Nurbs surface. But this is the most simple method i feel personally for Moi (pun intended!)... In either case, it's OK to use a polysurface for this purpose since coil springs are not manufactured from 3D models. It's only for illustrations of mechanical objects. I think if you really want the curve deviation to be minimized, then we just start with more points in the initial array, and also we create many more extra points on each end before creating the helix to be trimmed away... Not perfect, but makes it simple and quick :)

jonah

SORRY - I was thinking this was in response to my tutorial on making a coil spring! http://www.moi3d.com/forum/index.php?webtag=MOI&msg=317.1 How embarrassing for me :) ...If using this type of spiral to develop an object for manufacture (such as threading on a moulded bottle) then yes i agree it is better to make a single spiral curve by drawing the spiral in it's full length. For most illustrative purposes either method should be OK....