Hi beetle, it's probably due to the bottom shapes on your first example, the "tubes" part at the bottom don't come to a common flat plane with the main body, each little tube has a just slightly angled surface at the bottom, here is a zoom in to the bottom area:




Things that are overlapping but at shallow angles to one another can tend to create a complex intersection since there will be a kind of partial area of overlap between the pieces (within tolerance) but not a complete overlap. Intersection curves in that kind of shallow case can end up kind of wandering around all over the place and that tends to make for problems gathering up distinct boundaries and partitioning areas cleanly.


Probably the easiest thing is to stretch the tubes out a bit so they don't end right near the end of the main body, let the tubes go a ways past the end and that would probably help avoid some of the most difficult to handle area. If you did want to have the tubes end right there you would want the bottom of the tubes to be more precisely flat so that it would overlap more fully with the bottom face of the main body rather than at a slight angle.

- Michael

Hi Beetle, I've attached an edited version here which should now boolean difference ok - the change I made was to go to the front view and slightly stretch the cutting tubes in the z direction using the edit frame, to avoid that situation at the bottom with partially overlapping pieces at shallow angles to one another.

- Michael

Also I noticed that the planar end cap surfaces on the cutting tubes is a generic "cubic" surface rather than an analytic plane surface, that may have happened as the result of a deformation command, when doing a Transform > Deform > Twist or Flow, the entire model structure gets converted from any "analytic" exact sphere, cylinder, or plane type specialty surfaces into generic squishy surfaces. Having analytic planes can help for booleans rather than surfaces that are just a general surface but that happens to be shaped as a plane. So in a case like this it could help to delete those end caps and reform them by selecting the surfaces and running Construct > Planar which will then put new analytic plane end caps on them.

I've made a note to myself to look into automatically reforming end caps like that to be analytic planes after doing a deformation transform.

But the easiest method is to make the cutting objects continue for a little ways past the end of the base object rather than having them stop right in the same spot.

- Michael