Hi Jesper,

> Regarding using a subtracting box that does not overlap with other parts of the model I actually
> have tried this so that it only covered the rod to be cut and then a little more of free space ..
> For some reason it didn't work ...?

That's actually why I did some of that cleanup work - when you have an edge boundary that is self-intersecting (crosses back over its self) it can cause the mechanism that determines which side is the "inside" and which is the "outside" of a solid to get confused.

The faces in particular that looked the messiest were these ones here:



It's hard to see what's messy about that right there, but if you get that face completely by itself you can see it's got this kind of squished tail sticking out of it:



That tail is a squished together boundary, some part of the trimming boundary is squished together and touching each other, that's the kind of thing that can mess up the sense of "inside" and "outside" in general.

So part of the cleanup was that I deleted all those piece and drew in new planes using Draw solid > Plane > 3pts in those areas and joined them in.


I think that there was possibly some kind of slight misalignment in this area here:






In order to get the bottom face to be built, I had to squish the outer and inner boundary down using "flat" snap (that's using the edit frame from the side and grabbing a corner and moving it down to squish things flat, there is a snap point that will kick in and if it does that means it was not quite totally flat to start with).

So a couple of things were on a very slightly different z level, just enough to kind of mess up a couple of things I think.

I found that one little tail sticking out piece by going through the process of deleting all the bottom faces because I wanted to see if I could make one single plane out of the whole thing, it's generally good if planar areas are made up of one big plane surface rather than little fragmented coplanar pieces, and sometimes looking in area where there are little fragments you can find the problem things like little slivery stuff.

Anyway once I got those things tuned up then I did not have any problems doing the booleans after that.


> I wonder how the need to tune up the ring may have appeared

The main thing was I was kind of suspicious about the bottom face being in multiple pieces, that could mean it wasn't all flat. Also this is pretty subtle thing but if you look here notice how this particular edge area is slightly darker than the other ones nearby it? :



The presence of a darker area like that usually means that there is actually more than one edge overlapping on top of each other in that one area. The anti-aliasing around curves basically gets darker the more times that a curve is drawn over the same screen area. That's often times a cue for me to zoom in and investigate that particular area - that's the spot where the little leg is sticking out from that vertical plane. The leg is made up of a couple of edges that go out a ways and then another edge that doubles back again.

So that kind of slightly darker edge display in one area can sometimes indicate some kind of anomaly in the model which might need to be fixed up. The easier thing to look for is that you want areas that should be planar to be made up of one big plane. To clean those up you can delete the existing fragments and then use Construct > Planar to build a new big single plane and if Construct > Planar does not work it means there is some problem with the various pieces not actually all being on the same plane, there may be some pieces that are sticking out a bit and need to be cut off or some pieces that are slightly higher than the others and need to be moved down just a bit.


Hope this helps explain what I was looking for and what I did for the cleanup!

- Michael