In the attached file I have a red and gray shape.
Problem Union.3dm.zip (548.9 KB)
If I do a boolean union, Rhino appears to discard the red shape leaving the gray.
If then UNDO and do the boolean union a second time, Rhino says “Boolean Union Failed.”
I am on a roll with odd behaviors using the same basic shapes.
In the attached I have a red and blue close polysrf. If I boolean intersect the two, the red shape disappears and the blue appears to remain unchanged.
Problem Intersect.3dm 2.zip (439.5 KB)
dear @miano
your details are less then 0.07 inches, your document-unit-tolerance is 0.01 inch.
normally your document tolerance should be at least 1/10 better 1/100 of the details you will model.
in general it is not a good idea to decrease unit tolerance (increase precision)
setting the document unit tolerance to 0.0001 and the boolean works … but the resulting data might be not suitable as steps before have been done with less precision.
hope that helps - kind regards - tom