Hi Jesper,

> Regarding your suggestions for trimming/separate & boolean subtract I'm not quite clear about the difference
> and what exactly you suggest but I'll take a look at it and see if I can learn something new.

So for this part, it's a general technique that if you want to modify some small portion of a kind of complex object (like in this case you wanted to slice off just those legs and not really modify anything else), it can reduce the complexity of what's going on to separate out that particular chunk of the object into a separate surface, then do some surface modeling work on it like trimming it with a line, and then once you're done you can rejoin it back to the main piece again.

That method can get things done even in the presence of some kind of degenerate geometry or whatever type of thing might be confusing the more "higher level" operations like booleans.

So in a case like this that would mean some steps like - select these 2 surfaces that make up one of the legs:



Now run Edit > Separate - that will break those selected faces off into a completely separate object. You can now hide the other main object and just work for a little bit on only this much more simple object:




There's a lot less stuff that can possibly go wrong on this kind of object. Once you have finished manipulating this one piece doing booleans or Trim or whatever (Trim is a surface modeling method, it just cuts surfaces up, it's less complex in general that the booleans. The booleans are kind of like a "high level" trim that incorporates Trim + automatically picking pieces to discard or keep based on which volume they are in followed by joining those pieces back up), and then once you're done select your new piece and the original big object and use Join to glue them back together into a solid.

You don't always need to do that - it's just a technique that can possibly be used to simplify the amount of stuff that any particular operation has to deal with, so it can get things done when you are running into problems.

If you're not running into any problems then you would just want to stick more with using booleans, they can get things done more quickly. But they can get confused in the presence of self intersecting geometry.

- Michael