Alternative way to cut/subtract geometry when BooleanDifference fails?

I have what should be a relatively easy BooleanDifference operation. It fails. So instead I’m going through a multi-step process just to create an opening. I’m trying to subtract the grey from the purple:

The intended end result is nothing special, just an opening through a slab:

image

I’m surprised that BooleanDifference can’t handle this. Even if I export to AutoCAD and subtract geometry, and import back in, I can get the intended result. Is there something better than BooleanDifference for operations like these?

In what way did it “fail?”

Hard to tell from the images what is going wrong - please post a file with just the two parts before the attempted subtraction… Maybe the box to be subtracted from the purple part is coincident with one of the walls and that is causing the hangup.

You can also try Wirecut or MakeHole with the top profile of the cutter box… But it should do the same thing.

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in those cases, run intersect and see if you get closed intersection loops

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Sometimes shifting the geometry a bit can help. If this is acceptable for your project/output. Another thing is to make sure the initial volume is closed. You can check that in the Properties. If it’s not closed you can start with the “Cap” command. Or close holes another way.

Otherwise, it may have to do with the fact that this is a topologically strange volume. You could boolean split it first into two pieces to remove your doughnut hole, boolean difference with your other volume and then boolean union to bring it all back together.

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A combination of basically everything suggested here helped. I think that every situation is probably a little different and there isn’t a single all-encompassing solution. Once I tried the suggestions out I was able to re-built the geometry in maybe a minute or two, and have it “closed” (I need everything closed so that it looks right in sections). I think a better mindset is to simply be grateful when “BooleanDifference” works, but be ready to take additional steps if it doesn’t work.

I could post files… but I don’t want anyone to waste too much time fighting with my garbage :wink: . I’m modelling a concrete parkade and at the same time, trying to find workflows (and a level of detail) that actually makes it a practical endeavor. Even tailor-made programs that cost $1,000’s (per year!!!) struggle to create accurate parkades. I’m hoping to find maybe yet another niche that Rhino can fill.

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Hi Keith - please do - we might be able to sort out what’s going on and either get it on the bug pile or tell you how to avoid it.

-Pascal