Hi All

Some assistance required here please.

I have made a Helix with an  OD of 780 and ID which is irrelevant but lets say 700. Plate thickness of 6, one revolution and a pitch of 820. Once this is flattened and placed in a drawing I'm getting an OD of 875.

The same dimensions inserted into Sigma Nest and worked out manually an OD of 822 is achieved.

Any suggestions why this is?. Things like this make one doubt the outcome of a model.