Sweep along a helical curve

hi

I am try to create   a model something similar to drill using helical curve and sweep I have followed following step

1. Create a helical curve using the equation

2. Create a sweep featuring by using the helical curve as the trajectory

3. I have created the sweep section as ball nose profile.

the radius profile moves along the helical curve but the straight line does not cut along the helical curve.

kindly help  I have also attached the image.