I can’t figure out why boolean union fails when I try to merge the two models together ( the towers) to delete any unwanted surfaces from the inside.
i attached the file if someone could help and thanks in advance
boolean.3dm (13.0 MB)
booleans only work on closed polysurfaces/surfaces.
your tower sections are all open. use “selOpenPolysrf” and you will see.
but since the openings are flat, “cap” works to close them and then uniting the towers is possible without any issue
boolean (1).3dm (13.1 MB)
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thank you . But, i have a question please , could i make the inside of the towers void instead of solid?
you have to extract a face from the closed tower to open it or explode&group… or disable clipping plane fills in your active display mode.
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Actually Booleans work with open surfaces and polysurfaces in many situations. It appears that for the Boolean operations to work the intersection of the two objects needs to be a closed curve or multiple closed curves.
Alternative 1 to Boolean operations:
Trim - or - Split and Delete unwanted portions.
Join
Alternative 2 to Boolean operations:
Intersect - or - IntersectTwoSets the objects, preferably with the current layer being a layer with a bright, easy to see color.
Trim - or - Split and Delete the unwanted portions using the intersection curves as the cutting tool.
Join
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yes. thanks for clarifying!
What I meant to say is that the object you want to perform a boolean operation ON should be a closed object in order to get a reliable result.
But it is well possible to use a single open surface to cut away a portion of a closed polysurface.
using booleans on open object, can sometimes work but often yields strange results like this:
the output is a single polysurface where the second bool object (the plane) is fused to the first object
Trim is in deed the better choice in such cases.
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thank you so much
not in wireframe 
check shaded
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