A finger joint or comb joint is a woodworking joint made by cutting a set of complementary rectangular cuts in two pieces of wood, which are then glue

Glue

This is a list of various types of glue. Historically, the term "glue" only referred to protein colloids prepared from animal flesh. The meaning has been extended to refer to any fluid adhesive....

d. To visualize a finger joint simply interlock the fingers of your hands at a ninety degree angle; hence the name "finger joint." It is stronger than a butt or lap joint

Lap joint

In woodworking or metal fitting, a lap joint is a technique for joining two pieces of material by overlapping them. A lap may be a full lap or half lap....

, and often contributes to the aesthetics of the piece.

The history of the finger joint is believed to have begun with wooden produce boxes or crates in the days before modern, man-made materials. Finger joints were originally cut by hand with saws and sharp chisel

Chisel

A chisel is a tool with a characteristically shaped cutting edge of blade on its end, for carving or cutting a hard material such as wood, stone, or metal. The handle and blade of some types of chisel are made of metal or wood with a sharp edge in it.In use, the chisel is forced into the material...

s. In modern times they are easily and quickly made with a table saw

Table saw

A table saw or sawbench is a woodworking tool consisting of a circular saw blade, mounted on an arbor, that is driven by an electric motor...

 or router

Wood router

A router is a tool used to rout out an area in the face of a relatively hard workpiece, typically of wood or plastic. The main application of routers is in woodworking, especially cabinetry....

 and a jig or fixture, which can be shop-made or purchased from a specialty woodworking supply store. A finger joint jig typically consists of a moving fence with an indexing pin that is used to evenly space out the cuts. The fence is moved over a cutting blade making a cut that is then moved over the indexing pin so the next cut can be made.

While it is relatively easy to make using computer aided manufacture, a table saw or a wood router with a simple jig, some common problems include:
- Tear out on the back side
- If using a table saw, the top of the joint may not be exactly flat, depending on the tooth set of the blade
- Spacing problems and difficulty dialing in the exact index

Properties

The strength of a finger joint comes from the long-grain to long-grain contact between the fingers, which provides a solid gluing surface. The number of contact points also allows for more gluing surface as opposed to a butt joint

Butt joint

A butt joint is a joinery technique in which two members are joined by simply butting them together. The butt joint is the simplest joint to make since it merely involves cutting the members to the appropriate length and butting them together. It is also the weakest because unless some form of...

 or a rabbet

Rabbet

A rabbet is a recess or groove cut into the edge of a piece of machineable material, usually wood. When viewed in cross-section, a rabbet is two-sided and open to the edge or end of the surface into which it is cut....

 joint.

While the spacing of finger joints is mostly an aesthetic decision, it is commonly less than or equal to the thickness of the material being joined. For example, one might decide on 1/8" fingers on 1/4" material unless the length of the mating surfaces lends itself better to a 1/4" finger joint, which would appear less "busy" to the eye.

Although finger joints are usually evenly spaced, it's not unusual for woodworkers to experiment with varying spacing between cuts.

Applications

The finger joint is the most common joint used to form long pieces of lumber from solid boards; the result is finger-jointed lumber

Lumber

Lumber or timber is wood in any of its stages from felling through readiness for use as structural material for construction, or wood pulp for paper production....

.

The finger joint can also be invaluable when fixing tables and chairs and also can be used in such things as floor boards, timber roof and door construction. This is also used in design technology for students. Finger joints can be hard to make without the right tools.