To get a strong splice on wooden beams, you must use a scarf joint. A scarf joint exposes a large amount of the beam's wood-to-wood glue surface area. In addition, a scarf joint blends in nicely and is unnoticeable once it's sanded and finished. Scarf joints on beams are done by hand with a band saw to cut an extreme angle on both pieces to be joined. The scarf joint is strong and is an effective way to splice beams without using bolts or metal brackets.
Lay the beams on their sides on a flat surface. Lay a 12-inch ruler diagonally across the end of one of the beams on the end that you want spliced. The ruler should touch the edge of the beam on one side and angle across to the other side.
Draw a line diagonally across the beam using the ruler for a straight edge. You should have a steep angled line running across the edge of the beam, coming to a sharp point on both sides.
Turn on the band saw and place the end of the beam on the band saw in front of the blade. Cut along the length of the line.
Lay the cut beam on top of the beam to be spliced. Align both beams and using the pencil, trace the angle from the fresh-cut beam onto the beam on the bottom.
Hold the second beam to the bandsaw and cut the angle that you just drew.
Lay both beams together with the angled surfaces opposing each other. Spread glue along both fresh-cut angled areas.
Shoot 6 pin nails evenly spaced through the thin ends of the angle on both sides of the splice using the pin nailer hooked up to the air compressor.
Place 5 hand clamps evenly spaced along both sides of the beam across the scarf joint. Apply even pressure to the joint until glue oozes out the length of the joint. Wipe off any excess glue. Wait 24 hours for the glue to dry.
Remove the clamps and finish by scraping off any residual glue. Sand the splice with a belt sander. Finish by sanding it with an orbital sander using 100-grit sandpaper.
Use an assistant help you to hold the beam up to the bandsaw to get the cut straight if the beam is very long or heavy. Lay plastic sheeting under the splice to prevent excess glue from leaking out on the floor when clamping the joint together.
Always wear safety glasses when working with wood.