Cross-lap joints consist of two pieces of wood or metal joined together at right angles by overlapping them in the middle of one or both members. Precise measurement results in a cross-lap joint with the mating parts neatly interlocked, their faces flush. In some cases, the joint is strong enough on its own and no longer needs nails, screws, or glue. Tools of choice for building cross-lap joints include table saws, routers and shop jigs. Cross-lap joints come with a couple of variations and find use in a wide number of applications.
Cabinet framing constitutes one of the biggest uses for cross-lap joints. They provide excellent amounts of strength, even with little to no reinforcement. A cross-lap joint's shoulders prevent diagonal distortions called "racking," especially when strengthened with dowels or fasteners. You can find cross-lap joints in nearly all internal cabinet frames, providing ample support using a minimum amount of materials. Cross-lap joints are used in much the same way in shoe racks, book and kitchen shelves, and other similar projects.
Cross-lap joints are also found at construction sites, where they're used in steel cross-bracing for buildings. They serve a crucial role, supporting compression and tension forces and increasing the building's overall resistance to earthquakes. Similar applications can be seen in trellises for climbing vines, braces for stretchers and torsion box ribs.
Furniture Cross Supports
When it comes to supports for furniture, cross-lap joints offer big advantages over other joint types in that they tend to be sturdier, less obtrusive and more aesthetically pleasing than simpler lap joints. In some cases, the joint itself serves as support and decoration. They're more complicated than full- or half-lap joints, but building them is fairly easy. Examples of furniture that make use of cross-lap joints include chairs, workbenches, dining and coffee tables and beds, where visible wood joints are acceptable or even desirable.
Crates, Grids and Ladders
Cross-lap joints have a couple of special variations, namely the edge cross-lap and the middle- or T-lap. Edge cross-laps overlap edge to edge rather than face to face, and have notches rather than shallow dadoes. Edge cross-laps are commonly used to make egg crates, grids and box compartment dividers. The T-lap, on the other hand, has one section's end overlapping with the other section's middle and is used in ladders, wooden crates, gates, railings and some types of window trimming.