Hi Don,

> TurboCAD can use surfaces, but that term used in TC
> may mean something different than what others mean
> when they talk about surface modeling.

The reason I was asking about that, was that it used to be pretty common for CAD programs to be oriented primarily on working with solids and individual surfaces were only used as a way to slice off a piece of a solid.

It could be possible that TurboCAD is set up along those lines - if so then that means that you'd want to make your object in MoI to be a fully closed solid before exporting it into TurboCAD if you wanted it to stay connected together over there.

MoI is what is sometimes called a "hybrid" modeler where you can work on surfaces that can then be glued together at their edges to form a solid (in MoI the Edit > Join command does this) , and also a solid can be broken down into individual separate surfaces (in MoI with Edit > Separate). In a hybrid modeler you can have an object that has several surfaces joined together into a connected piece but without it necessarily being a solid if it has some open edges on it.

A lot of programs that used to be focused just on handling solids (SolidWorks, etc..) have over time become hybrid systems.

- Michael