From David Henderson:
When you tape enough annuli together, it will be clear to you that
the geometry is not that of flat annuli [just like the strake, the curvature
of the outer helix,
especially when we went to the auger, showed us that we had a different
geometry than a flat annulus]. The more annuli you put on, the
more you will ruffle at the edges, until the ruffles become unmanageable.
Tape together enough of the annuli so that you get a ruffled surface.
Annular Hyperboli Planes by Daina Taimina