Hi Paul,

> Yes, the surface is still there but if the trim curve is within the
> boundry you can select and untrim it but if
> it happens to run to the outer edges you are stuffed !!

I think you already figured this out, but to make sure - when a trim runs to the outer edges you can still remove it, but you must select all the edges for the entire loop, not just one.

So for example if you have this situation, don't select just this one edge:




Instead you must select all these edges for untrim:




It is on my list though to improve untrimming to make the first type of selection work though, I'm not sure yet when that will happen.

Also a shortcut can often be used to select all edges - first select one and then do Select/Select All (or Ctrl+A) - When select all sees that there is a partial edge selection it will go through and select all the other edges of a surface or solid.


One last note - when you have a closed surface like a cylinder for example, then the "seam" edge of the cylinder can also be part of the full trimming boundary loop so you sometimes have to select it as well to get the whole loop.

- Michael