Scarf joint

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A scarf joint

A scarf joint (also known as a scarph joint) is a method of joining two members end to end in woodworking or metalworking. The scarf joint is used when the material being joined is not available in the length required. It is an alternative to other joints such as the butt joint and the splice joint and is often favoured over these in joinery because it yields a barely visible glue line.

The scarf joint is not preferred when strength is required, so it is most often used in decorative situations, such as the application of trim or moulding. The scarf joint is commonly used in construction fit out tasks, including fitting of skirting, picture rails, dado rails or chair rails, handrails etc..

Traditionally, the scarf joint was common in ship and boat-building and forge welding. Often, especially in shipwrights' work, the basic wedge was modified to give some degree of tensile strength to the joint. The joint was finished by bolting it or perhaps strapping it together. Iron bolts and straps were normal in carpentry while copper clench bolts were used in wooden shipbuilding. A competently made forge weld held itself together without reinforcement.

A scarf joint may also be used to fix problems caused when a board is cut too short for the application. The board can be cut in half with a tapered cut yielding a scarf joint. When the joint is glued together, the tapers are slid against each other so that the two sections are no longer in line with each other. This has the effect of making the board longer. Once the glue has set, the board can be planed down to an even thickness, resulting in a longer but thinner board.

[edit] Applications

Moulding, trim other decorative applications where the material is not available in the lengths required
Lengthening a board that has been cut too short
Guitar headstocks, to reduce the wood required to have a tilt back headstock on a straight wooden neck.

[edit] Methods

The joint is formed by cutting opposing tapered ends on each member which are then fitted together. When working with wood, this gives better long grain to long grain gluing surface, which yields a stronger joint than would be achieved with a simple butt joint. The tapers are generally cut at an angle between 1:8 to 1:10. The ends of the tapers are feathered to a fine point which aids in the obscuring of the joint in the finished work. A related joint is the hooked splice joint which resembles the scarf joint except that the tips of the tapers are not feathered in this way but are blunt.