It may be a helix - in which case the radius remains constant and the
height changes at a constant rate as the angle increases/decreases.

I was watching an episode of 'This Old House - Classics' and they had a
tour of a company that made spiral and curved stair cases. The stair railing
were made of laminated pieces. To get the proper curve for the railings,
the company had a series of open framework cylinders for jigs. There were
different size cylinders for different radii of stair cases. The rise of the stair
case was laid out directly on the cylinder. The strips of wood were glued
and then bent around the cylinders and clamped in place. The open framework
of the cylinders was necessary since it allowed attachment of the clamps.

Even with slow setting glues, speed was important since there many pieces
of wood to make even a modest sized spiral railing.