Hi wimverbe, so that's actually sort of a bug in Sweep, but it's also related to the small size of the little tiny arc pieces in the corners of your profile shape.

Part of the process of doing a mitered sweep is that MoI internally generates the sweep along each path section separately and then the pieces are intersected and trimmed with one another.

That "intersect and trim" process can have some difficulty on pretty tiny pieces that begin to approach the general 0.001 unit fitting tolerance size. Several kinds of operations in MoI like surface/surface intersection are carried out to some level of precision, and the default is basically 0.001 units, but if the entire size of the shape being processed is also right around that same size it can cause the intersection mechanism to get confused.

So you could either leave out those little tiny arc pieces in the corners and just have straight corners there, or also if you scale the entire thing up by 10 times in size it will then work ok because those little pieces will be just large enough then to avoid being in the same general size as the intersection tolerance.

I may be able to fix this up though by updating sweep to use a tighter intersection tolerance for very small sized profile segments, I'll take a look at that.

But you may in general run into problems similar to this with such little sized features with operations that involve intersection calculations. Sometimes it is best to leave things that are that tiny out or to work at a somewhat bigger scale (but not too big though either, just not so that individual features are around 0.001 units in size).

I am in the gradual process of tuning more and more things in MoI to use a "relative tolerance" mechanism where it uses a tolerance that is a fraction of the object's bounding box size rather than just a fixed 0.001 value, which is what should fix this particular case up as well.

- Michael