Hi yophie - it's because the curves you are trying to trim with each other do not actually touch each other, there seems to be a pretty significant gap between them, about 0.25 units or so:



It looks like the curves in the upper third area did touch the edge, that's why those ones worked.

When they don't touch each other the regular Trim function is not going to be able to find an intersection between them. It is possible to do an "apparent intersection" trim, if you switch to the Front view, and make sure the checkbox for "Project intersections" in the Trim options is turned on and then you can cut them to the 2D projection of the edge curve but there will still be a gap between them since they don't touch each other in 3D space.

re: align points - there is a script that will place a point object at the start point of a curve, it might help - it's available here: http://moi3d.com/forum/display.php?webtag=MOI&msg=2888.11 it it's the opposite point you end up needing (the end point of the curve rather than the start point), you can edit that script in a text editor and change the part that says .getStartPt() to instead say .getEndPt() and save it off as a new script which will create an end point instead of a start point.

Hope this helps!

- Michael