I am trying to join these objects together to be hollow by using by using " boolean union " , but it keeps failing. How could i solve this problem or is there an alternative command ?

thanks in advance

There is a good FAQ about Booleans failing.

Had you posted the file, I would have run the Intersect command to find the curves that would be used to Split the surfaces. My guess is I would find gaps or problems with those curves, which would be a good clue as to there the problems are with the polysurfaces.

**Which specific polysurfaces are you trying to Boolean?**

You model has both Open and Closed polysurfaces.

Here’s the link tot he FAQ:

https://wiki.mcneel.com/rhino/booleanfaq

these 3 polysurfaces

I can’t determine where are the polysurfaces opened.

I will check the FAQ, thank you!

Select 1, 2 and 3, Invert the selection and Hide to get the other objects out of the way.

1 and 2 are Grouped, so Ungroup them.

1 is an open surface. I have no idea what you expect to do with 1.

The ShowEdges command set for Naked edges will paint the edges so you can see them. I’ll ignore it for now.

2 and 3 intersect cleanly so they will Boolean.

Thank you !