Loft command with Developable option frequently produces surfaces which have significant differences from a true developable surface. These differences can be large enough to be unacceptable for work such as boat design. This particularly seems to occur when the middle of the developable surface is relatively flat. An example is attached.
Loft with Developable option surface:
It was created so that the correct developable surface is known exactly and is two adjoining conic sections with continuous curvature between them.
Loft Fail 11.3dm (463.8 KB)
Both the exact developable surface and the result from Loft Developable are included along with the result from DevSrf which creates a correct developable surface. While the Loft Developable surface unrolls “within tolerance” (whatever the tolerance is) it differs considerable from the exact surface. Section and “waterline” curves are included which can be compared. This screen capture shows the difference. The gold curves are on the Loft Developable surface, and white curves are on the exact curve.