"Sorry no there isn't any way to do that for mouse rotation. But it is possible to set up the arrow keys so they will do rotations, see here: http://moi3d.com/forum/index.php?webtag=MOI&msg=6145.2"

This kind of locked rotation is very useful to judge the design of an object from all sides
while refining its shape incrementally. Make a little change- rotate and judge, another
change.-rotate, etc. Like a model on the end of a catwalk ;-)

But : The rotation is is not smooth as it works with steps of 3° and it rotates pretty fast.

Is there any way of making the rotation smooth and slow ? Thx TOM