Woodworking Joints Guide

Wood joints are used in everything from furniture making to home building. Attaching two pieces of wood (sometimes called joinery) can be as much art as it is engineering. Different jobs require different wood joints-there are many ways to provide varying amounts of strength and style.

There are two common ways to create wood joints: mechanical and non-mechanical. Mechanical wood joints require the use of nails, screws or other non-wood elements to hold the wood pieces together. Non-mechanical wood joints use only wood to keep the wood pieces joined.

Non-Mechanical Wood Joints
Non-mechanical wood joints are created by creating a pocket in one piece of wood and a matching projection on the other. The projection fits tightly into the pocket and glue or tension is applied to hold the two pieces of wood together. Non-mechanical wood joints are structurally very strong, but can take lots of practice to perfect. Some of the most common types of non-mechanical wood joints are:

  • Tongue and groove - tongue and groove joints are typically used to join the long edge of two pieces of wood. A groove is cut into the side of one piece and a matching projection (the tongue) is cut into the second piece. Tongue and groove joints are commonly used for flooring and wall covering.
  • Dovetail - A dovetail joint is created by cutting a series of triangular-shaped sections (called tails) from the end of one piece of wood and matching sections (called pins) from the other piece of wood. The tails and pins interlock to form a strong 90-degree joint. Dovetail joints are technically complex and are often used to create drawer boxes for furniture.
  • Splined Miter - A splined miter joins two pieces of wood at a 90-degree angle. Each piece of wood is cut at a 45-degree angle on a router table (called a miter cut) and a groove is cut into the back of each piece. A separate piece of wood (called the spline) is cut to fit into the groove. The spline is typically glued into place. Splined miter joints are used to create frames or other edgework.
  • Through mortise and tenon - To form this joint, a round or square hole (called a mortise) is cut through the side of one piece of wood. The end of the other piece of wood is cut to have a projection (the tenon) that matches the mortise. The tenon is placed into the mortise, projecting out from the other side of the wood. A wedge is hammered into a hole in the tenon. The wedge keeps the tenon from sliding out of the mortise.

Mechanical Wood Joints
Mechanical wood joints use nails, screws or other devices to hold the joined pieces of wood together. Typical mechanical wood joints include:

  • Butt - To form a butt joint, one end of a piece of wood is placed against the side of another piece of wood. Nails or screws are attached through the second piece of wood into the end of the first piece. But joints, while simple, aren't very strong.
  • Lap - A lap joint is created by cutting away half of the thickness of each piece of wood. The pieces are then overlapped to form the joint and joined by nails or screws. A lap joint create a strong joint, but leaves the fasteners exposed.
  • Biscuit - To form this joint, a special tool is used to cut grooves into each piece of wood to be joined. To join the two pieces, an oval-shaped piece of wood (called a biscuit) is glued into the grooves. The biscuit swells as it absorbs the moisture from the glue, causing it to wedge the two pieces together. Biscuit joints are very popular in modern wood working.
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Well-made dovetails joints are the sign of a true woodworking craftsman. Long honored for their strength and beauty, dovetail joints are common in cabinetry and furniture making. These tight joints are used to make the sides of drawers and decorative boxes.

Using a biscuit joiner makes easy work out of creating a strong joint between wood pieces. The biscuit joiner is a special saw that cuts crescent-shaped slots in each piece of wood to be joined. These holes are filled by an oval-shaped piece of wood called a biscuit.

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A box joint is a good alternative to a dovetail joint, since the box joint creates a very strong joint without the complicated cuts required by a dovetail joint.

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