The file below shows before I did a two rail sweep on the teapot spout which was succesfful (black curves).
bbefore 2 rail sweep.3dm (76.5 KB)
before 2 rail sweep.3dm (76.5 KB)
Then I tried a union between this spout(grey) and the body(red) and it failed. I’ve looked closely and cant find why its not working
failed boolean union.3dm (283.3 KB)