A jointer and planer are mechanically similar; a set of knives powered by a motor and removing stock from the board’s surface. There is often a bit of confusion between the functions of the two machines, and the question arises as to whether they can be used interchangeably. Do you really need both? The answer is “yes, you do,” and here is why.

Before talking about jointers and planers, it’s important to understand the mission, which is to create S4S lumber. S4S stands for “surfaced four sides” — all four sides are machined flat so the two faces are flat and parallel to one another, and the two edges are parallel to one another and square to both faces.

Let’s break it down into a four-step sequence to illustrate the differences between a jointer and planer.

Step one: Mill face #1 flat. The process starts at the jointer, where you lay the board face down and run it through to establish one flat face. This process is called face jointing. The jointer uses its offset in bed height to determine how much material is removed.

Step two: Joint edge #1. Now we take the face that was just flattened, place it against the fence and run one edge through the jointer. At this point we have a flat face, and one edge that is square to it. That is where the jointer’s work is complete, and we move to the planer.

You might be tempted to just flip the board over at that point and face joint the other side, but the reason that you don’t want to do that is that you will not produce a face #1 that is parallel to face #2.  A jointer uses the infeed table and fence as references so it can only flatten a side, it cannot reference off an opposing side. Face #1 and Face #2 will never be parallel with this approach.

Step three: Plane face #2. The planer has the unique ability to reference off face #1, and machine face #2 so that the surface is flat and parallel to it.

Step four: Rip edge #2. After you have achieved the desired thickness with the planer, move over to your table saw for the final step. Place the jointed edge against the fence and rip the opposing edge. At this point you will have achieved the goal; S4S lumber.

If you have saw blade marks on edge #2, you might want to make a light pass on the jointer to remove them. Do not get too aggressive because each pass on the jointer will take edge #2 out of parallel with edge #1.

Source: Paul Mayer is a guest blogger on Laguna Tools’ website. For information on Laguna Tools call 800-234-1976 or visit LagunaTools.com. More tips and projects online.