First we will create base. Create Linear CV curve.

Then go to surfaces/revolve option box, set y for axis.

Revolved surface will look like this

Create upper parts, using same tool

Then from side view create one linear curve, that has same start and end point (use curve snapping or c key+mmb drag)

 Then go to revolve option box, but set angle to 10.

This will create only 10 degrees out of circle.

Then select isopram at the front and go to surfaces/planar

Do the same for back isopram

Then group those three surfaces

Duplicate it 5 times for 60 degrees