What is the minimum length of a scarf joint?

The minimum length of a scarf joint is specified as 15 times the material thickness because this dimension ensures the joint's strength and effectiveness in distributing loads across the connection. A scarf joint is a type of joint commonly used in woodworking and aviation applications to join two pieces of wood at an angle, allowing for a seamless appearance and a strong bond.

Having a ratio of 15 times the thickness provides an adequate surface area for adhesive bonding and helps to minimize the potential for failure along the joint. By having this length, the joint can effectively handle stresses encountered in aviation, where safety and structural integrity are paramount. This standard is widely accepted in industry practices to ensure consistency and reliability in construction and repair.

In contrast, the other choices—5 times, 10 times, and 20 times the material thickness—do not align with established best practices for scarf joints. Lengths shorter than 15 times the thickness may not provide sufficient strength, whereas lengths excessively beyond 15 times may be unnecessary and could complicate the manufacturing process without offering significant benefits. Therefore, the correct answer emphasizes a balance between strength and practicality in design and engineering.