Merge solids as one single object

I’ve been trying boolean union, but it doesn’t look one piece as you can see in the picture.
it is a chair and I want to make the armrest and seatback as one single object

Most closed volumes in Rhino are closed polysurfaces which are several surfaces joined together. It is not possible to represent a shape such as the chair as a single surface. BooleanUnion does not merge multiple sufaces into a single surface. Instead it creates a single polysurface from multiple polysurfaces and/or surfaces.

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so there is no way to make them as one single object?

Hello - you can make them into one single object, but not one single surface, in this case - that is the result will be a polysurface no matter ow you get there. Here, the faces that meet are not planar - coincident faces generally fail in Boolean operations if they are not planar. You can do this at the surface level by trimming what appears to be the back of the chair with the edges of the arm. Post the file and I’ll take a look.


@Zane0413 What is your objective? If it is easier moving around or copying, you are better off by grouping the parts rather than trying to boolean those. After you have merged them in a single object/surface, it will be much harder to edit them at a later stage.
And even when your objective is 3D-printing, I have found that slicing software like Cura has no problem with handling multiple objects and print them as one, providing the parts have surfaces that coincide properly, or even better, interfere by a small margin.


I have solved the problem in my way. Thank u everybody. appreciate.

It sounds like you’re all set now but I wanted to add a tip in case you also plan on filleting. If those two parts are joined either manually through Trim and Join or by BooleanUnion and you then want to fillet the edges, I would suggest MergeAllFaces to merge the coplanar faces before using FilletEdge. This will reduce failures with the fillet surfaces trimming into the model. Less edges = less problems


If the edges are coplanar, you can do MergeFaces or MergeAllFaces.

If the edges are tangent, you can create a custom display mode and disable the display of tangent edges. Then they will look like one surface even if they are not implemented as one surface.

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Thanks, I’ll give it a try next time:)