And just one more comment on Rebuild - one of the other uses of Rebuild is to simplify a curve's control point structure. That's why the default tolerance is 0.01 units, because a tighter tolerance also needs more control points.

But 0.01 units deviation will be too large if you want to build joinable surfaces using the original the the rebuilt one for surfaces that meet up.

Things need to be no more than 0.005 units apart to be joinable.

So you'd need to use a rebuild with something more like a 0.001 tolerance for this case, or really it's probably better to discard the original curve and only use the rebuilt one for all the next surface construction so all the surfaces come from the same curves.

- Michael