Hi Mark -

> It does make me chuckle though, since that curved
> outline was originally created by mapping a flat shape into
> the inside of cylinder using the curve command...

Yeah so actually you wanted to try and construct your starting solid directly off of that initial planar piece rather than doing a projection of it.

This is kind of a frequent mis-step in general - it's pretty natural since it is kind of easy to focus on the outer edges of the final result that you want to get. But often times those final edges are actually easiest to get from the result of a cutting operation rather than trying to create them directly as the first step.

When that's the case you need to kind of not worry about those final edges when constructing the first shape - instead try to get a basic simple and extended shape and then once that is in place cut it up. That kind of goes for a lot of different situations as well - like if you've got some kind of complex boundary for a surface a lot of times you won't want to build the surface directly along that boundary initally but instead build it as a broader and more simplified extended shape and then cut it to get the final boundary in place.


> I don't understand when you should use the trim command
> to do something like this and when you should use the
> boolean commands.

The trim command is a surface modeling operation - it's something that you would generally only use if you are working with some individual surfaces to build your model up kind of one surface sheet at a time. That's a different kind of overall strategic approach than working with solids.

You should generally use the boolean commands instead of Trim if you are working with solids - the booleans are focused on operations between volumes. So using a boolean to cut a solid will produce a solid result, leaving things like the extruded side walls of the cutting objects in place to make the result also a sealed off solid.

Using Trim will always cut a solid into a non-solid because it operates at the surface skin level and not at a volume level like booleans.

See here for some more description and visual examples of the difference between Trim and Booleans:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3883.3


You could basically describe Trim as more of a "low level" operation. The boolean commands are kind of like a high level cutting construct that basically combine surface trimming along with automatically detecting which pieces to discard based on volume containment, followed by automatic joining of things back into solids.

Sometimes the more low level approach of doing the trimming and joining steps manually can be useful for difficult situations, but if possible you can gain some more convenience and a more streamlined number of steps if you can use solids and booleans instead of low level surface trimming, so it's generally a good idea to stick with working with the solid modeling approach and use booleans when it is possible to do so.


> I thought that that was what I was getting when I used the "join" command.

No, the join command is more like a kind of grouping mechanism - it make a new curve object out of those segments, but the segments are still individual child objects of the curve, it doesn't do things like fuse segments together automatically. In the future I may try to do something like that, but there are other situations where it is not necessarily good to fuse segments together so it's kind of tricky to handle automatically.

- Michael