Inversing the way of milling from top to bottom with "tube operation"

Dear community.
In V5 there is a vector "M" called "Machining direction" with the "tube function" : so you can switch from bottom to top and from top to the bottom.

I cant find it in 3dExp...so the milling is always from bottom to top....and i cant switch it..Somebody can help me ?
 

thank's a lot