3D Studio Max
Make a primitive Cylinder 8 segments
Apply a rotation of 1/16 of turn i.e. 22.5° to the y axis
With the 3DSnap activated at MidPoint, insert vertecies as in top on the right.
Adjust the new vertexes like above (Move on axis Z and non-uniform Scale on axis X for User).
Use Chamfer Edge to duplicate the edge.
Adjust the round-off.
Continue to model the original object and the copy will be updated in real time.
Finish by applying Make Planar to this polygon.