Using open polylines that define the flow of your cuts is acceptable as long as both of the polylines are going in the same directions and are above the top of the part. You may use Geoshape and Start Point Edit if you need to be sure of the direction of you flow lines.
During cut you will be prompted not only to select the surface or solid to cut, but for your flow lines as well.
Using the MCADFLOW.dwg file, select the XNURBS_CUT-FLOWCUT Cycle.
Select Slice Settings to be sure the Slice Vertical Angle is set to 0.0, and the Slice Mode is Zigzag.
Press the Cut Button.
The output of these settings should produce a tool path like this:
Slice Angle of 0.
Erase the previous tool path, then change the Slice Settings Vertical Angle to 90.0.
Press the Cut Button.
The output of these settings should produce a tool path like this:
Slice Angle of 90.