See
http://mecsoft.com/phpbb/viewtopic.php?f=7&t=2964[/url]
When the tool has a smaller cutting diameter than the shank, RhinoCAM can crash the shank against the work.
MecSoft tells me that this bug is in all their software, as of this date. (March 21, 2015).
The reason we don't see it so often is that it's common to use tools like this in a situation where there is no possibility of the shank contacting the work ... for example, cutting a groove in a flat plate.
But in my case, the work was a complicated 3D object, and I just told RhinoCAM to cut (horizontal finishing), assuming that it would do as well as possible without crashing the tool into the work. The example in the MecSoft forum is much-simplified from the real thing.
So watch out!