In spline joints, which grain orientation is correct?

• A. The grain direction runs along the joint
• B. The grain direction runs with the grain
• C. The grain direction should run across the joint
• D. The grain direction is not important

Answer: (C)

Grain orientation changes how strength and failure happen in a joint. For a spline joint, placing the grain so it runs across the joint means the wood fibers are oriented to help resist forces that try to slide the pieces apart along the joint and to hold the spline firmly in place. This cross-joint orientation provides better shear transfer and helps prevent tear-out or splitting at the joint as the pieces are clamped and loaded. When the grain runs with the joint, the fibers align with the load path in a way that can make the joint weaker and more prone to splitting or loosening over time. So, orienting the spline so the grain crosses the joint gives the strongest and most durable result.