Here is the step by step construction of my giant 585-hourglass and the 297-Water Drop (click on the photos to enlarge).
[Edit]: Warning! Deprecated method. You will find a faster and more efficient way to build hourglass bulbs here.
This old construction method should be replaced by the one mentioned above.
Once you've built your 2 bulbs, you can resume here in this thread (from the second picture).
The set of rods (294) to build one of the two bulbs:
As I changed the color scheme at the very end I don't have quite the right number of color rods here. But that's not a big deal, it doesn't change anything at the construction stages.
First, build a simple Lobel frame with a triangle as central polygon.