Hi Steve,

> So I need to ask again, "Is the problem with the boolean,
> or with the sweep?"

It's exactly the same answer as previously - it appears that the problem is in the surface/surface intersector which is one part of what the booleans depend on.


> I have attached a simple model of the ring, this was constructed in
> another 3d app. when imported into MOI, the pipes can be booleaned
> away without a problem (both pipes are 6 dia).

It looks like in your particular example here, those sweeps have somewhat lower accuracy and have a slight undulation to them, which avoids them intersecting exactly at a crown point. That actually helps to avoid the intersection bug though which seems to be related to things touching more exactly at a single point.

If you take the 2 tubes in your example and do a boolean union between them, you can see that the junctures between them look like this:





Note there that the intersection curves are not touching at a single common point - that's the difference between this and the other situation that has intersection problems.

It's pretty easy for differences in shape like this to produce different intersection results, and if there is a bug in one kind of intersection result, having a different result may avoid the bug - that appears to be all that you are seeing in this case.

It's pretty similar to the workaround of using slightly different radius values, it is producing a different kind of intersection rather than the "meeting at a single common crown point" one.

- Michael