Step #1: SplinePrevNext
- 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″.
Step #2: Spline (continued)PrevNext
- 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.
Step #3: Cutting SplinePrevNext
- 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.
Step #4: Sizing The SplinePrevNext
- 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.
Step #5: PrevNext
- 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.
Step #8: BevelPrevNext
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.
Step #9: GluingPrevNext
- Using a small brush, apply a thin layer of glue to all of the surfaces of the mortise and to the bottom of the spline.
- Put the spline in the mortise and using a scrap to protect the surfaces, tap it in with a hammer.
Step #10: Fitting and FlushingPrevNext
- The spline should be just proud of the surface and tight around the edges.
- Flush the spine by sanding or planing the surface. If sanding, be careful not to over-sand the area around the spline, especially if the spline is harder wood than the board.
- If planing, be sure to skew (hold plane diagonal to direction of cut) as you pass over the spline to help avoid tear-out.
- And that's it. A simple but cool little joint. This technique can also be used for joining boards together for tabletops etc. If a gap is desired, keep a thin piece of wood clamped between the boards while cutting the joint and then remove it before assembly.