create fin on helix surface

Here is a step by step for what i think you are asking.

1, Create a helix of the dimensions you require.
2, Sweep a circle profile along the helix.
3, Create another helix along the outer edge of the sweep feature.
4, Create a large helix to represent the outer edge of the auger flight.
5, Convert the most recent two helices into 3D sketches in individual sketches for each.
6, Insert a lofted bend using the converted sketches.

Following on from your message, is this what you aim to achieve?

https://bit.ly/2KNLTJV