How To Make A Lap Joint

A lap joint or an overlap joint as it is often referred to, might be required in any woodwooking project. The lap joint is much stronger than a butt joint. Figure 1 shows two versions of a lap joint.

The lap joint can be made at the ends of a piece of wood or anywhere along its length. The primary advantage of the lap joint is that it provides a larger surface area for the adhesive to hold the joint together and the surfaces are not strictly end grain, allowing for a much stronger glue joint then would normally be obtained with a butt joint.

Figure 1 - Two versions of a lap joint

In most cases the lap joint is made by removing half of the wood, as shown in Figure 2, on both pieces of board. However this is not necessary in order to create the lap joint. A lap joint could have 3/4 of the wood removed from one piece and a 1/4 of the wood removed from the other. As long as the finished joint assembly is the same thickness as the individual pieces of wood, you have created a lap joint. It may be noted that in most cases the notches are 1/2 the thickness of the wood on both boards.

Figure 2 - Half of wood removed on one piece of lumber to make a lap joint

Also a lap joint does not have to be at a 90° angle. The pieces of wood could intersect at any angle, and in fact lap joints are often used to join two lengths of wood together as shown in Figure 3.

Figure 3 - Lap joint - length wise

Optimum lap joint strength, for joining two boards together lengthwise, is obtained when the lap, as shown in Figure 4, is four times the thickness of the wood. Of course the longer the lap, the more strength the lap joint will have.

Figure 4 - Optimum strength of lap joint

As well, lap joints can be made to appear as 45° angles, as shown in Figure 5.

Figure 5 - 45° angle - lap joint

You can obtain additional strength from the lap joint by using nails and/or screws through the joint as well as the adhesive.

Dowels can also be used through the joint for both aesthetics and added strength.

There are many tools that can be used to make lap joints. The choice of tool is, in many cases determined by the physical size of the piece of wood that the woodworker is working with. Lap joints can be made by using a router, a dado saw blade, as shown in Figure 6 with a standard blade by cutting the piece of wood from the board or with a dado saw blade, as shown in Figure 7 mounted on a table saw, radial arm saw or a circular saw. Of course the lap joint can also be created by using hand tools - chisel, mallet and back saw.

Figure 6 - Dovetail joint on drawer - two different colored woods

Additional Woodworking Joinery Information

Butt Joints

Dovetail Joints

Mortise & Tenon Joints

Rabbet Joints

Through Tenon Joints

Tongue & Groove Joints