Hi,

Jeff…The 6 points are fixture they are from an engineering drawing of a rudder top profile, and plotted using the drawings distance up from a datum and distance out from rudder centre line. The rudder tip has a small radius edge above and a larger one below.

I see it that there is just one mathematical curve line through the 6 points, and there can be one point on the circle where this curve could then end up to be tangent to the circle. If there are more than one I would like tosee an image of where they are. I have to trus in the fact that when this drawing was created 50 yrs ago they used splines (cane) and created the arc and circles to be feasible.

Lucios drawing looks good …as does yours. I need to study all methods shown here to see what is easiest and best.

Pascal,…yes I had trouble before and never recall a happy conclusion or one I understood, then couldnt find the thread to check.

I still think the interpCrv command could have an option to start tangent from curve, I just cant see how it is that in the scenario above there are a number of start positions on the circle, all of them tangent to it, for the curve to go through the points.

I ended up choosing line tangent from curve, selecting circle then first point, getting some idea of where the start would be, starting my interpCrv where that line started on the circle, and then using line tangent two curves and selecting the circle and the curve to further fine tune things, creating a new InterpCrv for the entire journey from circle to circle, ending up with a ‘looks good’ result !

Steve