Block instances will not select when in Boolean Difference command

I have a grouped ring of spheres, generated from a block instance. I can select it normally, however when I come to select it as the cutting device in Boolean Difference it wont select.

why… and what to do ?


Blocks are intended to be used as instances of a single set of geometry.
If you want to actually use the geometry for something like a Boolean, Explode it first so the block instance is replaced with a copy of the geometry in an editable form.

If you just want copies, then don’t use Blocks.
Does that make sense?

Take 2 minutes and read the Help article for Blocks. It describes what they are, what they are for, and the advantages of using them in the right situation.

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Hi John,
thanks. I have had a read. I feel the help on them could be a bit better, I am aware of some quirks, yet they are not there.

I have started making blocks of things like rivets so that there is less to slow up the file when worked with on the pc and certainly my laptop. They are for boolean operations, so if I explode the group, then do the boolean difference, how do I get them back to being instances afterwards ? Undo will also undo the boolean ? I didnt see an answer in help.


Make a copy, explode the copy, Boolean difference…

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Got it :smile:


3 posts were split to a new topic: Subobject selection in block instances

Hi, @Helvetosaur doing this tonight, cloned the BlockInstance, set it to a black layer, it went black though remained on the source layer, I need to do a boolean on it, exploded it, then join, asks to select objects to join, but will not select the exploded parts.

I am at a standstill, 2hrs and having used Block Instance I cant set them to a new layer, I cant duplicate them and separate them out, I cant explode one and then join and boolean it.

I cant get hold of the original that was many hours work, I cant do anything on what was a normal item, having BlockInstanced it. Undo doesnt go back to before the blockInstance, how do I get my item back so as to work on it ?

surely one needs a solid to boolean so after explode, one needs to join the surfaces together. It wont let me select them ! they select for a fraction of a second.

hate Block instances , total denial of moving fwd . lost me my object as well.


Whenever I do complex boolean operations, I make a new layer, and copy all the items being booleaned onto that layer, then I turn off my source layers. This way you can always go back to your original geometry.

Exploding a block is different from exploding a polysurface. If you have, say, a box within the block, that box will come out as a closed box, not six surfaces. So if your block contained, say, a bolt and that bolt was a closed object, then exploding the block gives you a bolt which you can boolean directly, no need to join it back together.

I suspect that the exploded parts you cannot select are closed polysurfaces or extrusions on which, you will recall, the join command does not apply.