Tip #29
Doing Jointery on Your Table Saw
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Pg. 1-3, Pg 4-6, Pg 7-9, Pg 10-12, Pg 13-15,
Pg 16-18, Pg 19-21, Pg 22-24, Pg 25-27, Pg 28, Table 3-1

Splines and Keys for Reinforcement

Figure 3-54. These ar etypical of the joints that are stronger when a spline is used; (A) simple miters; (B) cross miters; (C) bevel miters; (D) odd angle joints; (E) edge-to-edge joints; (F) segments; and (G) even butt joints.

It's always a good idea to reinforce a joint even though modern adhesives provide a strong bond. Splines, which can be used with many joint designs as shown in Figure 3-54, do an excellent job of providing the extra strength. A spline is simply a straight strip that is cut to fit grooves formed in the mating pieces (Figure 3-55). Since wood can split more easily along its grain than across its grain, splines should be designed so the grain is at right angles to the pieces to be joined.

Figure 3-55. Be sure the grain direction of the spline is across its short dimension or at right angles to the mating pieces. Click on image to see larger view.

Figure 3-56 demonstrates how splines are used to reinforce simple miter and compound miter joints.

Figure 3-57. After grooves are cut in the edge of stock, the splines are separated by making a crosscut.

Forming Splines-One way to form splines is to first cut grooves through the ends of a workpiece and then to cut off the ends by doing a crosscut as shown in Figure 3-57. The thickness of the splines will depend on how you set up for the initial groove cuts. The grooves must run across the stock so the splines will have correct grain direction.

Figure 3-58. Plywood is a very good spline material. Use a spacer on the rip fence to gauge the width of the spline.

Plywood is an excellent material for splines. It provides a lot of strength and you don't have to worry about grain direction. Cut the plywood to a width that equals the spline length you need and then simply cut off as many pieces as you need (Figure 3-58).

Figure 3-59. A blind spline can add much strength when pieces are joined edge-to-edge, and it can't be seen when it is installed this way. Cut the spline so the wood grain runs along the short dimension. Click image to see larger view.

Blind Spline Joint-Simple butt joints are often used when boards are joined edge-to-edge, but a spline can aid in the alignment of the boards and add strength to the assembly. A blind spline can't be seen (Figure 3-59). Warning: The upper saw guard is removed for this operation so work with extreme caution.

Figure 3-60. Stop blocks are used to control the length of the groove. Start the job by bracing the workpiece securely against the front stop block and then slowly lowering it to contact the dado acessory. Click image to see larger view.

Cut the groove as shown in Figure 3-60. The stop blocks, clamped to the rip fence, control the length of the groove. Brace the workpiece against the front stop block, as shown in the illustration; then very slowly and carefully lower it until it contacts the dado accessory and rests securely on the table. Then move the workpiece forward until it contacts the rear stop block. Lift the work carefully when you remove it, picking the back end up first.

The splines, which are shaped dado, should have grain running across the short dimension. Always cut the grooves first since it's no chore to form the splines to correct thickness. Don't size the splines so they must be forced into place. A slip-fit is best since it makes assembly easier and provides room for glue.

Figure 3-61. Spline grooves in miters, cross miters, and even compound miters can be cut this way, but extreme caution is required.

Spline Grooves in Compound Miters-One method of forming spline grooves in compound miters, with the table tilted to the correct angle and the rip fence used as a guide, is shown in Figure 3-61. The operator is responsible for holding the stock securely and maintaining its position throughout the pass. Warning: The upper saw guard is removed for this operation so work with extreme caution. An easier and more accurate method is to use the Tenon Master Jig.

When you are making splined joints, always form the groove first; then cut the reinforcement piece so it will be a nice, sliding fit.

Figure 3-62. Keys are tirangular pieces that fit into miter cuts like this.

Keys-Keys are triangular pieces that are often used in the manner shown in Figure 3-62 to reinforce miter joints. Notice the direction in which the grain should run. The thin stock you need to make the keys can be cut as shown in Figure 3-63. To keep small pieces of stock from falling through the table insert, position the blade as close to the left side of the insert as possible.

Figure 3-63. The thin material you need to make the keys is cut this way.

Always cut splines and keys so they are longer than you need. It's better to trim them and sand them to conform to project surfaces after they are installed and the glue is dry.

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