Butterfly Spline

"Arikata" is a method of stabilizing checks in thick slabs of wood in aesthetically pleasing way. It can be used for joining boards together for tabletops etc.

  • Author: Len Cullum
  • Time required: 2 hours
  • Difficulty: Moderate
  • Add Note x

When working with wider, thicker slabs of wood, it is not uncommon to have checking (cracks) in the surface, particularly at the ends. While there are a couple of ways of dealing with this, such as filling the gaps with wood or putties or epoxy, I prefer to leave it as it is, treating it as a feature instead of a flaw.

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Add Note Edit Step 1 — Spline  ¶ 

  • You need 1 spline for every 3-5 inches of checking.

  • Cut a couple out of paper and lay them on the piece to find the right size.

  • You can make it as small as 1/2″ x 1″ up to 1 1/2″ x 3″. Keep it on the thin side, between 1/4″ – 1/2″.

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Add Note Edit Step 2 — Spline (continued)  ¶ 

  • Using a piece of cherry measuring 1″ wide 2″ long and 3/8″ thick here.

  • Make sure the grain runs the length of the long dimension. Use an adjustable square to mark the center of its length, and then 1/4″ in from each side.

  • Use an angle gauge to draw lines from the outer corners to the center marks.

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Add Note Edit Step 3 — Cutting Spline  ¶ 

  • Make a cut along the center line to where the angled lines meet. This is a relief cut that will make it easier to chisel out the waste. Keep chisel flat.

  • Take a few small shavings down one slope, then rotate and take a few from the other side.

  • Continue taking shavings from each side until both are down to the line. Now flip and repeat.

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Add Note Edit Step 4 — Sizing The Spline  ¶ 

  • Determine its position along the check. For greatest strength, try to align the centerline of the spline with the line of the check.

  • When ready, carefully trace the spline once. If you are working on dark wood, cover the area with a wide strip of masking tape and mark on it. Put an ‘X’ on one end and a corresponding mark on the board to keep track of the spline's orientation.

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Add Note Edit Step 5 — "Wasting"  ¶ 

  • Use a router to create a quick flat-bottomed hole.

  • Set the router bit about 1/32 below the thickness of the spline so it can stand out and be flushed later.

  • Rout the mortise staying about 1/16″ in from the pencil lines.

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Add Note Edit Step 6 — Chiseling  ¶ 

  • Carefully chisel the lines at the ends and along one side. Do not chisel the lines away. Put the spline in the mortise and check the fit along the chiseled edges. Correct any gaps now.

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Add Note Edit Step 7 — Fitting  ¶ 

  • Use a marking knife to scribe lines along the unchiseled side. Only make one pass with the knife. You should be able to see why you chisel out one side at a time. The lines you scribed are usually inside of the pencil lines. Only push the spline in a little way. If you push it too deep you might not be able to get it out.

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Add Note Edit Step 8 — Bevel  ¶ 

  • If it fits, carefully pull it out. Using a knife or chisel, chamfer (bevel) the inside edges of the spline to help it slide in straighter, keep from damaging the edges of the mortise, and leave a little clearance in the corners for glue squeeze-out.

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Guide Add Note

Butterfly spline? It's referred to as a "Dutchman."

Casey Ertz, · Reply

While there is always some regionality to terms, a Dutchman typically refers to filling a defect with another piece of wood, thereby minimizing or hiding it. The Butterfly spline (aka arikata, bow-tie, spool spline/key and probably a few dozen more that I haven't heard) is arresting the split, but not filling or hiding it.

Len Cullum,