Bulb Finger Art! (Manipulate CNC slot scheme for asthetic, spatial & structural considerations)

Picture of Bulb Finger Art! (Manipulate CNC slot scheme for asthetic, spatial & structural considerations)
Bulb Finger Joints are useful and attractive co-planer joints for connecting different sheet materials which are very easy to produce with machines such as CNC routers, Water Jets & Lasers. A great benefit of these joints is the strength along the plane of the joint without having to glue/ weld.

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 :)

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Step 1: Basic Geometry Overview

Picture of Basic Geometry Overview
The bulbs are created by a vector slalom between regular circles that are tangent to each other.

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

Picture of Creating the Boundries for the Bulb Chain
Here i am showing the shape i want the Bulb Joint Chain to link within.  Here I'm creating a long eye type shape. The line dividing the form is the 'spine' which the chain will fall along. The form does not have to be symmetrical across this line here it is.

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.
DIY-Guy1 year ago
Spineally! An understandable method to make these fantastic finger joints. Thank you Idanen.