Round (axial symmetric) part - I wish to convert this to sheetmetal, and then have unfold/flatten work for pattern development.   In spite of studying various videos and tutorials (including insert>sheetmetal>swept flange) I can never seem to get it converted to sheet metal fully - in particular flatten never works.

There are no flat faces on this part, that seems to be part of the issue.

Thoughts?

thx

bmw