Woodworkers use scarf joints to bond beams or boards together end-to-end. Scarf joints utilise a long diagonal cut to give the joint as much glue surface as possible. To make a scarf joint you need a band saw that is capable of cutting through the beam cleanly. Scarf joints are very strong once the glue dries and due to their long connecting point, they are almost impossible to detect if the joint is done right.
Lay two beams out on a flat surface. Make a mark 6 inches down from one corner on one of the beams with a pencil. Place a ruler on the opposite corner on the same end, and draw a line diagonally down to the other mark. You should be looking at a sharp spear-like point drawn on the end of the beam.
Hold the beam up to the band saw horizontally and cut down the line, cutting the spear point on the end of the beam.
Lay the beam with the point on top of the other beam. Use a pencil to trace the spear point on the other beam.
Cut the point on the other beam with the band saw.
Spread glue liberally along both freshly cut angles. Lay the beams down end-to-end with the glue surfaces facing each other.
Place four hand clamps along the top of the joint and tighten slightly. Flip the beam over and place four more clamps along the joint on that side, corresponding with the other four clamps. Tighten all of the clamps as hard as you can. Wait 24 hours for the glue to dry.
Place plastic under the scarf joint when you tighten the clamps to catch wet glue. Wipe off any wet glue with a damp cloth.
Try to hold the beams as close to horizontal when cutting, the end can tip down if the beam is over 96 inches long. Use an assistant if possible. Always wear safety glasses when working with wood.