A butterfly is a small, wedge-shaped (or two inverted tripods or pyramids, if you prefer) piece of wood used to hold a larger piece of wood together. Large boards often split when being worked with, especially depending on the environment they’re kept in. A butterfly can be inlaid against the wood grain to prevent these large boards from pulling apart.
A router is used to make the butterfly. When looking at the bottom of the router plate, you should see a brass collar, when making a butterfly you will need a brass washer to fit on top of this first brass collar. The thick, brass washer that you use should be exactly 1/8th of an inch, the exact diameter of the bit you will be using. When you finish cutting the hole that the butterfly will be inlaid into, you will remove the brass washer to cut the butterfly itself.
First make a template for the butterfly. The router will use this as a guide to cut both the hole and the butterfly, ensuring that they will be the same size and shape. It is recommended that you draw the shape on a piece of rigid cardboard, such as a cereal box, and then trace this shape onto the wood that will be used to make the template. The template should be about 3/8th of an inch thick, the exact thickness of the washer on the router that you will be using.
Set the correct depth (about 3/16th of an inch is how much you will cut into the wood) and the correct stop on the router. Then use the router on top of the template the cut the hole for the butterfly in the piece of wood you will inlay. Clean the rough spots out of the hole with a chisel. If the edges of the hole are round, also square then off to be sharp.
Now you will cut the insert, the butterfly itself. Use the same template on top of the wood to cut the piece. Remove the brass washer and trace the shape of the butterfly with the router. You should only need one or two passes to make the butterfly. Use a table saw to remove the butterfly from the wooden board if necessary. Set the correct depth and width for the table saw and shave the butterfly off of the board.
If the edges of the butterfly are rough, use sandpaper to clean them up. When you have finished, the butterfly should fit exactly into the hole in the board, much like a puzzle piece.
To finish the inlay, glue the butterfly into its hole and allow the inlay to dry overnight. The next day, lightly plane the boards to make the surfaces even. The butterfly should initially be a little “proud” of the board so that it can be planed and given a final sanding.
You can use this same technique to make any shape and size inlay by simply replacing the brass washer and adjusting the depth and width of the tools. Compared to making inlays by hand, this technique is both much quicker and much more accurate. If you do not own the tools necessary to perform this technique, you can purchase router inlay kits specifically designed to make the process as simple as possible.