This Instructable shows the simple geometry behind this joint and explains how to draft this & how you can adapt its form to allow for greater control of the technique and hence the overall design.
I'm explaining this in terms of drafting it with programs that can export to the manufacturing tools capable of fabricating these components, though the form can be achieved with a basic compass set.
Thank You TechShop Detroit for helping me with this design :) www.techshop.ws
Step 1: Basic Geometry Overview
Specifically, at the diagonal tangent of eachother about a stright line (spine) being slalomed.
This means that if you draft a circle and draw a perfect X through its center to the circumference, the intersection of this line with the circumference should meet along the 'spine' of the connection, joining with the same point of other circles.
This way the circles are stringed together by these diagonal tangents alternating along this spine. Once the chain is complete all you need to do is delete the shorter segments of each circle or create a new layer and trace as you want using this as a framework.
Step 2: Creating the Boundries for the Bulb Chain
If your using a CAD program, once you have established this form you can lock the layer and start a new one using this as guidelines.