Butterfly Key Joinery - Part I
posted on May 25, 2006 by Rockler

As the blog's editor, the honor of presenting the first in a series of woodworking projects has (somehow) fallen to me, and after giving the matter much thought, I've decided to take a shot at a technique I haven't tried for a few years - installing butterfly keys.  Each week, for the next four weeks, I'll work on one phase of the process and keep you posted on my progress. If you have any questions or tips to offer along the way, be sure to let me know.

Butterfly key joinery is used either to join two pieces of wood, or as a repair on a single piece of wood.  A "butterfly" shaped key is cut to fit into a corresponding mortise that either crosses the two pieces of wood to be joined, or a check, crack, or other defect in an otherwise sound single piece of wood. The two flared ends of the key hold the two pieces of wood - or adjacent sides of the defect - together in the same way that the interlocking pins and tails of a dovetail joint hold the members of a drawer or a box together.

Apart from producing an exceptionally strong joint, butterfly keys are one of the most visually appealing joints you can make. Butterfly keys used in an inventive way as both a structural and decorative element in a table designed and built by Pennsylvania woodworker Tom Noone*.  The two halves of the table's walnut top are held at a distance of about 1/4" form one another by two curly maple butterfly keys.

I was first introduced to butterfly key joinery in college by a visiting artist who had served as apprentice to the millwright for the United Kingdom's Society for the Protection of Ancient Buildings. He used the technique in part as a repair and visual design element on pieces of wood with defects that he found aesthetically interesting.  In his honor, I'll be using butterfly keys to mend the piece of 5/4 jatoba pictured here - which, as you can see, offers plenty of opportunity for me to hone my skills.

There are probably many ways to "correctly" install butterfly keys, so if you're new to the technique and want to give it a try, check around to find the method that suits you best.  The first few steps of the one I'll be using will be to cut the key with an Ikedame dovetail saw, trace the key's shape onto the piece of jatoba, and then route the basic shape of the mortise "freehand" with a plunge router.  After that, I'll trim the edges of the mortise, glue in the key and trim it flush with the surface of the Jatoba. In Butterfly Key Joinery - Part II (next Wednesday or so) I'll mark and cut the keys, and pass on my method (and any others that I hear about in the mean time) for making sure that the keys fit into the mortises correctly.

*Tom Noone's table was featured in the March/April 1992 issue of the Woodworker's Journal.  A complete set of plans are available at the Woodworker's Journal website.

posted on May 25, 2006 by Rockler
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