Router Technique to Bridge a Crack

Although the end result is beautiful and looks complicated due to the precision fit, the key to this joint is applying a simple router technique that is detailed in this video. At a high level, the steps for the overall process include:

Choose the location. You’ll want to choose a spot that can provide the maximum holding power over the crack, as the natural forces of expansion and contraction will be working against the butterfly. If the crack is quite long, don’t hesitate to install multiple butterfly joints to achieve maximum stability.

Cut the butterfly. No need to use a template or try to be overly precise; just create a shape that is pleasing to the eye and has plenty of holding power with the appropriate angles. Position the long axis of the butterfly in the direction of the grain to maintain maximum strength. You’ll rough cut on the bandsaw and clean up with a sharp chisel.

Installation. Here’s where your router technique comes into play. Install a small bit in a plunge router, and use careful freehand technique to remove the bulk of the waste. Your router technique should get you close to the line, but make sure to leave a slight buffer and do not cross the line. After the majority of waste has been removed, pare to the line using a chisel.