Unroll developable surface problems


Let's see if anyone can help us with a Prostructures problem on unrolling surfaces

We have a steel half conical type surface with a length of 20m, a small radius of 2m and the larger radius of 5m and when we measure along the length of the smallest curve edge it has 6.2832m and the biggest 15.7080m.

After using the command "Unroll developable surface" with U and V points with a value of 255 those curve edges have the following lengths, smallest 6.2853m and the biggest 15.7134m.

Also the straigths edges have 20.2237m on the surface and after unroll it has 20.2245m

Can anyone tell us why those differences in lengths ??

We also have tried with other type of surfaces and the measures along the edges are never equal after unrolling them.

Thank you in advance for any help


Carlos Moura