BooleanUnion fails


When I prepare two objects and execute a BooleanUnion(Overlay two objects.), they are not all integrated. (Refer to the photo)

What should I do?!

The Boolean operations first find the curves of intersection between the objects. The Intersect command does the same thing.

Then the Boolean Splits the surfaces using those curves.
Then based on the command you selected Rhino knows what to delete and Join.

The most common reason for Booleans to fail is the intersection curves aren’t usable.

This implies the process to determine Boolean failure.

Here’s the FAQ:

Thank you very much for your answer.
This is a difficult problem for beginners.
I try one by one and solve the problem.