I hate Boolean Union !
I have rebuilt curves, created surfaces avoiding iso’s heading into one corner, bad practice for all nurbs.
they use a common line between them.
Used patch for the end ones.
join surfaces, then select the joined surface, run command solid extrude surface along line,
it asks me to select surfaces, yet they were selected, so select them one by one, choose red line,
get three solids, all made in exact same direction, their surfaces touching because the surfaces touched and were made to common lines, and joined at those edges, so it was happy then.
boolean union the resulting three separate solids on the black layer, fail…
BooleanUnionFail.3dm (220.9 KB)