Watched a video titled “Creative People Who Are On Another Level (Amazing Skills And Talent)” and saw this guy build a wooden spiral out of half circles.
So wrote a GH model for it, more complicated than I thought, more complicated than necessary?
Interesting to play with the parameters. Depending on ‘Circle_R’ and ‘Count’, there is a minimum ‘Spiral_R’ (radius), below which breaks the spiral. Switch in blue group joins the half circles into a continuous spiral.
Grasshopper quirks! 
When PFrames ‘N’ (Count) is any value other than 3 or 4, the frames are aligned consistently with X-axis horizontal and pointing toward the center. When ‘Count’ is 3 or 4, they are not horizontal and require corrective alignment (yellow group):
Different issue: when ‘Count’ is 3, Angle ‘R’ (Reflex) must be used instead of ‘A’, hence the corrective action in the cyan group.
When ‘Count’ is 30, 33, 35 and perhaps other values, Pipe fails. 
Two other known issues with this code that I didn’t fix:
Due to flattening, it fails to handle multiple circles. (easily fixed)
It works only with circles, not arbitrary curves like ellipses or radiused rectangles,
(not easily fixed!)
