I'm trying to draw a steam dome flare which changes radius.  On the top of the boiler the radius needs to be 1.33mm (as in the right hand dome) but as it drops down it needs to increase to a maximum of 4mm (as in the left hand dome) at the bottom.  I've tried to do this in autocad, 123D design and blender but they all appear to only be able to do a constant radius fillet.  I can see two ways of doing it, but both are long and slow.  The first is to draw a series of profiles and loft them into a