Boolean Operations Problem

Hey all,

I just got Blender today and i started a model of a passenger car.

I was able to use the boolean difference operator to cut out one part of the undercarriage but when i tried to use it again to put in the wheel-well the entire program “performed an illegal operation” and quit. I tried reopening and reinstalling an niether worked.

The time that worked was using a rectangular prism and the time that didn’t was using a stretched cylinder.

Any suggestions?

Thanks in advance.

Yes. Boolean Operations need closed bodies to work. So it may be that one of the objects was not closed.

This should give an error message, but it seems that at least the linux blender version does crash.

Yup that was the problem exactly. I found the search link. :wink:
I checked out the undercarriage and there were two places where there weren’t faces.

I fixed it and tried it again and it worked. Or so i thought…
The outcome was confusing.
I ended up with the original cylinder (or an identical copy) and the car body was attached to another copy (an incomplete copy that is) of the cylinder. there is no other copy of the car body.
It’s almost like a union, but i set it to difference; several times.

any suggestions?

Thanks again

it was fixed to raise an error for the non modifier version but only after release was it noticed that the modifier path hadn’t been fixed. It is fixed in CVS, and will be fixed in a bug fix release.


Hey all,
Heres a couple more questions in my quest to fix my problem.

Is there a function that tells me if and where my mesh isn’t closed?


How do i rotate my view around the selected object along a single global axis?


To find the holes, you can try “select non-manifold” (it’s Alt-M I think, can’t try, rendering; or it should be in the “select” menu). It selects edges with not exactly 2 faces connected to them.

<EDIT>Of course it’s not Alt-M, since that’s “merge”. It’s in the select menu in edit mode and the hotkey is CNTL-ALT-SHIFT-M… (thou I seem to remember having seen a simpler one, but I cant find it anymore)</EDIT>

Thanks Mexx,
That select non-manifold really helped. It found the relevant edges in no time.

However, When I try the boolean operation again it comes out really wierd; in the affected piece, the part that should have been subtracted still has remnants of the cylinder that was doing the subtraction. And its not just extra vertices that i can get rid of, its full faces that stick out of the side and down. Sometimes even most of the cylinder.

Any ideas on how to fix this one?

Also, I would like to be able to reuse the couplers for other models and i was wondering how i should save them once they are built and how to add them to a model when i need them.