Why autocut not working here?

I can’t manage to cut the rail with my curve. What happens? autocut.3dm (90.9 KB)

I don’t know what autocut really means - do you mean Wirecut? I do see a problem when using WireCut in the Front view. That’s because your rail volume object is not closed and is actually flipped inside out. If you use Flip on the object then you can wirecut it correctly with the curve. But I recommend you just fix the volume so it’s really closed.

HTH, --Mitch

The polysurface isn’t a closed solid which you can see with ShowEdges>Naked Edge display or with the What command. ExtractSrf the top surface with the curved end and delete it. Then make a Sweep2 surface and join it back in. Wirecut from the front view will work as you expect after that.