Step 1
Join two boards at the end with a lap joint. Saw halfway through one board, 4 inches from the end. Saw from the end of the board to the cut, and remove the excess wood. Saw the other board the same way, also removing the excess. Spread glue in the notches created. Place the two boards end-to-end, and clamp them together. Secure the pieces with strap iron screwed onto the sides of the join.
Step 2
You can also join two boards with a butt join. Square off the ends of the boards. Bind them together with a piece of strap iron, fastened with screws to the edges. Place this type of join on top of a support, and nail or screw the board ends into the underlying support.
Step 3
Or you can structure a long, thick beam from shorter boards. Place the boards end-to-end, as if for a butt join. Spread glue on the first layer. Place another run of boards on top of the first run, staggering them so that the unbroken parts of the second layer will cross the joins of the first. Clamp the boards together, then use wood screws to firmly pull the board layers together. Strap iron may be placed across the edges of the joins, if desired.