Step 1: Making the drop spindle's whorl
A couple of things to consider when designing the whorl are radius and weight. If the radius is too large the whorl may bump into things (like your leg) while you are spinning. If the whorl is too heavy it could break a fine thread, but if the whorl is too light it will stop turning quickly and you will be constantly having to flick it to keep it going.
It isn't actually the weight of the whorl that determines how long it turns -- it's the moment of inertia. Physics teaches us that if you want to maximize the moment of inertia of an object of fixed mass, that mass should be distributed as far from the center as possible. So the ideal whorl would have only thin spokes connecting a heavy rim to the center.
All of the whorls shown here work just fine.