Hi Chipp, it's because the tire part has end caps on it which overlap each other, making for self-intersecting object. Any time you've got pieces of an object that run right over top of other pieces it will tend to confuse intersection calculations.

If you formed this by Flow you would want to leave off the end caps on your base object that you are deforming, to avoid generating these types of overlaps.

Here I've hidden the outer surface of the tire so the 2 internal end caps are exposed so you can better see what they are:






I've attached a repaired version of your tire that has those internal caps removed and then separated and rejoined and without the self intersecting areas and the boolean should work ok now.

- Michael

EDIT: Burr is beating me to the punch these days! :)

""""""""EDIT: Burr is beating me to the punch these days!""""""

Except you explained what the "errant surfaces" are and are from...

Probably drinking our coffee's at the same time. :)

Thanks guys! Yes, it was created with FLOW. Good tip on leaving off the end caps. Wondering, with flow and a circular object, will it alway align properly, assuming the base and target files are set up correctly?

Hi Chipp,

> Wondering, with flow and a circular object, will it alway align properly, assuming the
> base and target files are set up correctly?

Yes, it ought to if everything is set up to match. I think it may not automatically join the open ends to each other though, that may require an extra separate/rejoin step if that's the case.

- Michael