Hi Wim, re: cannot_trim2.3dm - try doing boolean difference and pick the objects in the Front view, if I remember right (I'm away from my main computer for a bit so I can't double check at the moment) picking in a view that has a grid aligned to the lines will help disambiguate which direction lines will be projected out to when cutting planes are generated from them.

Over here doing that with boolean difference seems to work ok, I've attached the result.

Other things that may be generally problematic with your objects is the rather small numeric size of some of the features, like you've got a fillet with a radius of 0.002 units in there. I know that it may not seem to be a small value since you are using meters as the units but really the unit system doesn't really make any difference, things are considered "small" by the geometry engine if they have a lot of decimal places just in the numeric values that are used. There are some areas of MoI that can be sensitive when processing geometry that is close to the default fitting tolerance of 0.001 units. So it can be generally better to avoid making things that are small in numeric size like that, maybe use cm or mm for your units for things of that size rather than meters.

- Michael