Hi Kevin,

> Everytime I use the scaling rail I get a little tear in my
> nurbs surface just near the end. Is this a display error or
> likely to cause meshing problems later on ? (see attached image).

That looks like the kind of dropoff that can happen if the scaling rail did not traverse the entire length of the sweep, it basically can abruptly stop influencing the scale at that spot.

Here's an example with a one-rail sweep. Here is a one rail sweep with the scaling rail off to the side:




When the scaling rail is applied, the profiles will scale out away from their normal plane until they hit that scaling rail:




If the profile is not able to find any intersection with the scaling rail, it will just stay its normal size, which may cause an abrupt change in shaping.

Since the scaling rail is applied in this manner, it is not a bad idea to extend it a ways past the start and end of the sweep so that you know the entire zone of the sweep is totally covered with it.

If that is not what the problem was, I will probably need to look at the .3dm model file to see what is happening.

- Michael