Custom Cut Butterfly Joints

Handmade Graduated Butterflies Are Stunning

hand_cut_butterflyThe butterflies or ‘dutchmen’ embedded in this desktop are custom sized and cut on a bandsaw. Butterflies stabilize the crack and also provide a focal point on top of the desk to highlight your woodworking skills. When making butterfly joints, I tend to avoid templates available at woodworking stores. In my opinion, these templates result in blocky butterflies that have too steep an angle and aren’t as aesthetically pleasing. Besides, if you want something to look uniquely handmade, make it unique and by hand!!! I’ll show you how on a beautiful slab of elm I plan to use for a small side table.

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Make Multiple Mock-Up Butterflies to Check for Scale and Proportion

angle_finderI set my adjustable angle finder at 8 degrees and mock-up butterflies out of 1/8” plywood. I make multiple iterations in different lengths and widths, allowing me to slide the butterflies around and see if the scale and proportion are right, as well as check for positioning. I don’t have a formula for the dimensions of each butterfly, but too big, and the butterfly feels overkill, too small and it seems like an afterthought. I make mine 1/3 to 1/2 the thickness of the slab and utilize one near the edge and another every 5”-8”. The size of the butterfly has two references: the size of the slab and the size of the crack. They get gradually smaller as the crack gets smaller. Once I settle on the size, I transfer the dimensions to my butterfly blank, which I have made out of contrasting walnut, and cut out the shape on the bandsaw.

Sand the Edges of the Butterflies

stationary_sanding_block No matter how perfect my technique, the bandsaw blade leaves a slightly imperfect edge on the butterfly. To clean up the edge, I make a sanding block by adhering a half-sheet of 150 grit sandpaper to a flat block of hard maple with double stick tape. I align the waist of the butterfly with the crisp edge of the maple block and move the butterfly rather than move the sanding block. Five or six swipes on each facet of the walnut are all it takes to clean up the butterfly. Harder exotic woods may take longer than walnut, but this technique is still effective.

Mark the Placement of the Butterflies

trace_the_butterfly I carefully replace the mock-up butterflies with the real ones and trace them in place. A carpenter’s pencil isn’t suitable for this task, or even a #2, which is soft, and dulls easily. My pencil of choice is mechanical with a .07 mm lead. It’s thick enough to withstand rough wood grain, but fine enough to accurately mark an important tabletop cut. Because the butterflies will not be exactly symmetrical, it is essential to mark the orientation of each butterfly.

Mortise the Tabletop

palm_router_mortising I bore out most of the waste with Forstner bits and then clean the rest with a palm router. Because this procedure creates so much dust, I hold the router with one hand and carefully trail it with my vacuum hose. This way, I never lose sight of my pencil line. If for some reason I do go outside the lines, the fix is relatively easy; I make a new butterfly that is slightly larger than the one intended for the existing hole. No problem!

Chisel to the Line

pare_the_mortise After the bulk of the waste is cleaned out, I carefully pare to the line with sharp chisels, double-checking often with the butterfly to make sure I’ve not pared too much away. Pen-knives are excellent for cleaning out the acute corners. Once the mortises are cleaned out, I glue the butterfly in place with Titebond III. If the butterfly is an oily exotic species like Cocobolo, I use epoxy.

A Stable and Beautiful Tabletop

stable_and_beautiful_slab Once the glue is dried I saw off the top of the butterfly with a Japanese saw. Traditionalists are welcome to use a hand planes for the final finish, however the 90-degree opposing wood grain presents a potential problem. For me, I normally hand sand with the grain before applying finish. I prefer a random orbit sander, finishing with 320-grit sandpaper, which ensures there are no issues with tear out or cross grain sanding marks. Now, the tabletop is stable and beautiful. A winning combination!

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17 Responses to “Custom Cut Butterfly Joints”
  1. Jay

    I have also found putting a dowel vertically through the end of the crack will help keep it from progressing further into the board

    • WWGOA Team

      Hi, Matt!

      1/8″ spiral downcut is great for this. Gives a nice crisp edge with minimal splintering.

  2. Ike Kaiser

    Great explanation. Since your Dutchmen don’t go all the way through the board, do you put any on the underside?

  3. Seth

    Just out of curiosity, was the crack in this slab a real crack or was it cut for the demonstration? Either way, it looks great, I was just curious 🙂

  4. Bill H

    I have found using a heavier gauge xacto knife to mark my butterfly keys to be very effective. After I trace the key I go back and score the lines again, and they provide for perfect placement of my chisels when paring the edges.

  5. Star

    Thanks! I finally got a hit that wasn’t origami- this should help me finish my picture frame! 🙂

  6. AJ

    Just wondering what type of timber he used for the bench top and butterfly joints?

  7. Chuck

    Really good explanation. I’m just starting on my first slab tabletop and had been reading about approaches using a template and hadn’t liked the look of them at all.

    • BKF

      Check out Samurai Carpenter on YouTube. His approach is the one that I’m using on my Magnolia slab desk. Pretty easy to accomplish.