VDB combine intersection/difference not working cleanly

[bentway23]

I'm sure the answer to this will be something so easy, obvious, and profoundly stupid that my family and friends will all disavow having ever known me, but I'm stymied.

I am using an animated noise to create a lumpy VDB fog field, which I convert to SDF and then use VDB Combine to cut out part of a hero model. I'm cutting it into two interlocking parts, using SDF Union Subtract for one side and SDF Union Intersection for the other, and I will subsequently assign a different material to each part.

Originally I got it set up, no problem, with a standard AAnoise. I'm trying to get it set up with a periodic noise so I can loop it. The problem is that at the VDB combine stage, it doesn't subtract or intersect cleanly. You can tell something is happening, as there are little dotted lines on the resulting surface, and the occasional hole, but it's not cutting it out like I would like. I've tried different resolutions with the VDB from Polygons and that doesn't seem to make a difference. (I've actually run into this before, but I'll either rebuild the Volume VOP or fudge some numbers and it goes away. No such luck here.)

What obvious, stupid thing am I doing wrong so that the VDB combine isn't working like I'm hoping?

Thanks for help and forebearance!

sdf_union_problems.hiplc

[flcc]

Just reducing the size of the box, who is unnecessary big IMO, work for me.
I've no explanation.

[bentway23]

Thanks--unfortunately, that didn't work in the final project (the box is sized to the actual object I'm mangling). I tried transforming everything down to half size and doubling VDB resolutions to see if your approach worked, but the result was the same.

[j00ey]

If you increase the bandwidth of your sphere VDB it works, set it to 3. [Exterior Band Voxels that is]

Edited May 28, 2020 by j00ey

[bentway23]

Stepping up the bandwidth on the noise field to 3 did the trick--thanks!!