Scarf Joint

The scarf joint, illustrated in Figure 11, is generally recommended for high-strength hermetic seals on parts with circular or oval designs, especially crystalline resins.

The scarf joint requires that the angles of the two parts be between 30° and 60° and be within one and one half degrees. If the wall thickness is .025” (0.63mm) or less, an angle of 60° should be used. If the wall thickness is .060” (1.52mm) or more, an angle of 30° should be used. Intermediate angles are recommended for wall thickness between .025” and .060” (.063 and 1.52mm).

A minimum wall thickness of .030” (0.76mm) at the outer edge of the scarf joint is recommended to prevent “blowout,” or melting clear through the wall, during welding.

The scarf joint is not commonly used due to the difficulties encountered in maintaining component concentricity and dimensional tolerances. However, this joint is highly recommended when limited wall thickness preclude the use of a shear or modified shear joint.

A modified scarf joint is illustrated in Figure 12.

As shown in Figure 13, a flash well can be incorporated in the scarf joint to contain the excess molten material generated when the parts are welded. The length of the well should be at least equal to the cross sectional thickness of the part being welded.