Six Spiral Coasters

Six coasters based on Fermat's Spiral - http://mathworld.wolfram.com/FermatsSpiral.html - Spiral_coaster_4.stl is perhaps the most interesting one. It is based on two Fermat spirals, one rotated 90 degrees with respect to the other. The four ends are connected to interior points to form an approximate octagon. See the middle coaster in the above image.