Although often used for tabletops, you can use it anywhere to join the edges of two boards together. The key can actually be any size and shape you want to suit your application, although the traditional butterfly key looks like a dovetail. Make it from a contrasting wood for the best effect.
Inlay template guide
Cut out the waste
Cut the key
What You Need
The easiest way to make a butterfly key joint is with a bandsaw and chisel, particularly for thick stock. However, if you are only looking for a decorative effect, you can use a router with an inlay template guide and a pattern to make shallow inlays. An inlay template guide set includes a bushing (with Allen key), template guide, and ¼” spiral router bit. They can be purchased as a kit or separately, and come with complete instructions for making inlays.
How To Make The Joint
Since it is primarily a decorative joint, you should decide how the butterfly key size, location, and proportion will work with your project, and design it accordingly.
1. Align your boards together before gluing and draw the butterfly keys onto the boards. You can do this freehand, using a paper template, or by using a ruler to mark out a specific dimension.
2. Use a bandsaw to cut the waste out, being careful to keep the cut perpendicular to the surface of the boards.
3. Clean up the cut with a sharp chisel. Make sure the openings in each board match exactly when the boards are glued together. To do this, you can clamp the boards together before cleaning up the cut.
4. Position the newly cut openings over the material you want to use for your butterfly key and trace the opening with a sharp pencil or a marking knife. You could also use a template to mark the keys.
5. Cut out the butterfly key with your bandsaw. If your stock is small, use doublesided tape to attach it to a larger piece of wood for safety before cutting on the bandsaw. The final butterfly key should be slightly oversize.
6. Glue and clamp the boards together with the key glued in place flush with the surface of the boards. Sand or plane flush as required.
7. Glue and clamp the boards together with the key glued in place. Make sure the key is flush with the boards. Sand or plane flush as required. If you don’t want to make the butterfly key joint by hand, but want it to be more than just a decorative joint, you can use a matched set of bits like the ones shown. The 14º dovetail bit is used to make the opening in the two boards you want to join, and the matching 14º butterfly spline bit is used to cut the key.