Stages in preparing a 3D model for rotary machining.
1) Create a new empty model with the number of points you wish to use to represent the model you will machine.
Make the physical size suitable for the model you will be machining.
NOTE: The following step is important for these instructions to work!
Set the origin in the centre of the model - click in the middle of the white rectangle representing your job on the 'Create New Model' dialog