Thanks for the replies,
Actually I was thinking ahead a little. I was thinking of the large and variable fillet that goes between an airplane wing and its fuselage. I could model it rather easily but if I wanted to build the plane then I would need a template of the flattened fillet so that I could lay it in place. I could (and probably will) fill it with balsa pieces and then use some wood filler and then then sand to shape but it would be really cool to lay a pre cut piece in place and bend it back to shape.

Thanks again.

Hi bz, a fillet like you're describing is not a developable surface, which basically means it's not physically possible to form it out of a flat piece of stock and then only bend it into shape along a straight edge.

Any surface that has compound curvature in it rather than being straight in one direction cannot be formed from a flat piece without having lateral stretching taking place at the same time.

That's part of why the whole area of surface unrolling for physical construction is a fairly complex topic.

Your 3D surface has to have the shape of something similar to a cone or a piece of a cone in order for it to unroll to a flat pattern.

- Michael

Rhino has some tools in it for working with developable surfaces, some info here:

http://www.rhino3.de/design/modeling/developable/

http://wiki.mcneel.com/labs/devsrf

http://docs.mcneel.com/rhino/5/help/en-us/commands/unrollsrf.htm


Here you'll see how a complex curved surface made from bent planks does not really happen with a single bent piece, rather it's a set of strips with each individual strip being a developable surface:
http://www.boatdesign.net/forums/boat-design/designing-developable-surfaces-rhino-45275.html#post592264

Just any curved surface is not likely to be developable, especially a fillet going around a curved shape is not going to have a straight line shape to it in any single direction, in order to unroll a surface it has to have that straight line on it which is where it would be bent at in order to roll it up.

- Michael

Thanks Michael, your explanation makes perfect sense ...



bz