I'm trying to sweep a rectangle along a helix and keep the rectangle normal to the helix at all points along the sweep.  I positioned the rectangle at one end of the helix and swept it along the helix, but it is not normal to the helix at the other end.  It is important that the rectangle maintain a constant width along the entire helix; however, it does not do that if it doesn't stay normal.

The attached picture shows that it is correct at the end on top and wrong at the bottom.  The bottom ends with a knife edge, but it should be flat.

How would I go about making it stay normal the whole way?  I've tried most of the settings in the Property Manager for the sweep and helix.

Thanks in advance for the help!