The sketch at the right (Figure 1) shows the initial positioning of the two boards to be edge joined. The ends of the board are screwed together with a blocking board; a short 2x4 about as wide as the two board's total width. The saw blade is aligned with the seam between the two boards. The saw blade is adjusted to a height just above the height of the boards. This way only a small amount of wood will be removed from the underside of the blocking boards as the boards pass on either side of the saw blade.
Once the boards have passed completely through the blade, the outside board is unscrewed from the blocking boards pushed toward the board adjacent to the fence. If the two boards are aligned with no visible gap between them the process
is completed. If
a gap still remains, the blocking boards are again screwed
into the outside board, the blade is aligned to the center
seam of the two boards and the process is repeated until no
visible gap remains between the boards.
Once no gap remains, the blocking boards are removed, the board against the fence is put aside and the outside board moved against the fence. A new board is placed against the board next to the fence, the blocking boards are attached and the whole process is repeated until all boards to be joined have been put through the process.
This process will work even if you are using an inexpensive table saw with an inexpensive blade. When the blade moves or wiggles, the undercut in one board becomes an overcut in the other board. The end result is that the boards will still fit flush together.
An important part of the whole process is using a very long fence, that is, a fence that is just over double the total length of the boards you are joining. Although a long fence is not mandatory, it will make the edge joining job much easier.
It's a good idea to number each board (e.g., 1, 2, 3, etc.) to insure they are kept in the same sequence they were cut. After all boards have been cut, they can be joined together using biscuits or any other appropriate means.