Toolpaths in metal spinning are still designed by human operators, largely by intuition: a scientific basis remains elusive. In this paper, a parameterised toolpath is proposed based on a quadratic Bezier curve. Experiments are performed varying each of four design parameters in turn, to investigate how tool force, part geometry and various failure modes evolve with key features of the tool path. Analysis of these experimental results reveals some new features of process mechanics and leads to a proposal for a set of rules that may become useful for automatic toolpath generation.