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*Spline Joinery*

Spline joinery is one of the strongest methods of joinery used in woodworking. When glue is properly applied to a spline and to the joint area of the wood pieces being connected, a large surface area receives the adhesion properties of the glue. This forms a strong joint.

Traditional spline joinery requires cutting slots with a router or table saw. Small, thin strips of wood must then be cut to fit inside the slots and act as splines.

Newer methods of spline joinery use a plate or biscuit joiner to cut precise mating oval slots in adjoining boards. This biscuit joiner is a fast, simple, and accurate plunge-cutting tool that can be used to cut slots in hardwood, softwood, plywood, particle board, and other pressed woods.

Footballs shaped wafers, called biscuits, are then placed inside the slots with glue and used to help line up adjoining surfaces. When a water based glue is used, the biscuits swell in the joint, making an extremely strong and firm bond.


White glue, yellow glue, carpenters glue, hide glue and aliphatic resin glue are examples of water-based glues.(Photo3) This bonding technique has traditionally been limited to making edge-to-edge joints. However, with the use of a biscuit joiner, biscuits can now be easily used to connect butt, miter, and T-joints. Biscuit joining can be as strong as mortise and tenon, tongue and groove, standard spline, and doweled joints. In most cases the material around the biscuit will break before the biscuit itself will break. A greater surface area is exposed to glue in a biscuit joint, making the seams stronger.

A variety of spline joints can be made using the biscuit joiner. The number and size biscuits needed for each joint depends on the thickness of the wood and the length of the joint. In general, the small #0 biscuits should be used for miter cuts in ¾ in. materials. The larger biscuits should be used for edge-to-edge joinery.

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