Please help - Union converting materials in unwanted ways

I am wondering if there is a way to union parts with different materials and have them keep their respective materials?

I am asking because I am trying to rebuild a castle door I made but had certain measurement issues.

This is what I am trying to rebuild.

This is the door showing the union arch on top with the fill cylinder removed. As you can see, the cylinder , “fill” will overlap with the doors once placed inside the empty arch which isn’t ideal.

Thus, this is the only way I know to build so that I get the look I want but I don’t want to make two unions. Also, with the new automatic resizing/repositioning that happens with unions, I found trying to place the two parts a little tricky. It’s much harder to work with a part that is 7.989 studs instead of it’s original 8 studs. (OCD tendencies are not liking the micro gap)

This is how I want to build instead:

However, the union will randomly pick a material to make all the parts and that is not what I want at all. I may have tried to figure this out a few times (was also trying to figure out the resizing/repositioning “bug feature”)

Any help/tips would be appreciated.


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Unions will only take a material and colour of one of the parts that got unioned. So I suggest sticking to 2 unions.

Edit: And It is also not a bug feature for the scaling part. The scale tool will recognise it like a group and it will scale accordingly. So you might want to scale before making unions.


I do scale before I union. When creating a union, Studio will resize a micro fraction to solve some other problems they were having in CSGv1… unless I’m misunderstanding. What exactly do you mean by scaling accordingly?

this is what I’m talking about… I want my union to be 8x4x2.1 and could even understand it if was sized to include the negated part but I don’t really know how to compensate for the micro rescaling.

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and actually that was weird glitch size. Usually this union ends up resized as this

When making an arch, I usually have the inner part slightly larger, but also thinner. Or if the inner part has to be wider than the outer part, don’t have the outer part hollow.