Two machines, two jobs
A jointer and a thickness planer are often discussed together because neither can do the other’s work. The jointer makes a surface flat. The planer makes the opposite surface parallel to it. Using only one of them leaves a gap in the process, which is why woodworkers who mill their own lumber usually want both.
The jointer has two tables, an infeed and an outfeed, with a rotating cutterhead between them. The outfeed table is set level with the cutting edge, so as a board passes over the head, the cut surface rests on the outfeed table and the machine removes high spots. After a few passes, the face is flat. The jointer does not care about thickness. It cares about straightness and flatness.
The planer works the other way around. It rests the board’s flat face on a bed and cuts the top surface parallel to that bed. It does not make a flat surface from a curved one. A bowed board can be pressed flat by the rollers and spring back to the same shape after it is cut.
Put together, the jointer provides the flat reference and the planer provides parallel thickness.
The standard milling sequence
Most guides describe four steps for turning a rough board into a usable one.
- Joint one face. Take light passes until the face is flat along its length and across its width, with no rocking when you set it on a flat surface.
- Plane the opposite face. With the jointed face down on the bed, plane the other side until it is parallel and the board reaches the target thickness. It is often wise to leave some extra thickness for final sanding.
- Joint one edge. With the flat face against the jointer fence, joint an edge so it is straight and square to the face.
- Rip the other edge. Cut the board to width on a table saw, with the jointed edge against the fence, so both edges are parallel.
The result is a board with two parallel faces, one straight edge square to those faces, and a second edge parallel to it. This is often called “four-square” or “S4S” stock. Parts cut from it will fit together better, because the joint surfaces start out flat and square.
Projects that depend on this sequence
Furniture from rough lumber. Tables, chairs, bookcases, beds and workbenches rely on flat, square parts. Mortise and tenon joints, dovetails and glued panels all work better when boards start flat. Joinery tolerances are small, and accumulated errors show up as gaps or racked frames.
Wide glue-ups. Edge-joined boards only make a flat tabletop if the edges are straight and square. A jointer edge, or a good alternative, produces tight glue lines. Gappy joints are a common sign of poor edge preparation.
Doors and frames. Frame-and-panel doors, cabinet doors and face frames twist if the stock is not flat. A twisted rail or stile means a door that never sits right.
Turning rough stock into a consistent set of parts. Legs, aprons, stretchers and drawer parts that need to be identical are easy to get from properly milled boards.
Projects with expensive wood. Starting with rough lumber lets you choose where to cut, see the grain inside the board and control the final dimensions. Whether it costs less overall depends on local lumber prices and your tool costs.
Working with warped lumber. Boards that are cupped, bowed or twisted can often be salvaged by jointing and planing, though they lose thickness in the process. Severely warped boards may lose too much material to be worth using, so start with stock thicker than your final target.
Alternatives when you lack one or both
These are real options, and each has trade-offs.
- Buy surfaced lumber. Four-side-surfaced boards are sold at many suppliers. They are convenient, but they can still move after cutting, through internal stress and normal wood movement, so they may not be perfectly flat.
- Planer sled. A flat sled with shims supports a warped board so the planer can create a flat face. This works for one-off jobs and wide slabs, but it needs care and good support.
- Router sled. A router riding on rails can flatten wide boards or slabs.
- Hand planes. Slow but quiet, with no dust-collection demands and little noise. They require skill and sharp irons.
- Jointing on a table saw or router table. With a jig or a straightedge, either machine can create a straight edge.
- Mill shop services. Some suppliers will mill lumber for a fee.
A jointer with a short bed limits how well it flattens long boards, and a narrow jointer limits the width. Check the width of the boards you plan to use when you shop. A combination machine can save space but may require changing configuration between operations.
Safety
Both machines have exposed cutterheads and generate substantial chips and noise. Wear eye and hearing protection and a dust mask or respirator, and use dust collection. Follow the manual for minimum board length, thickness and width. On the jointer, use push blocks and keep your hands off the cutterhead and away from the area above it. Do not joint very short pieces or boards with loose knots, nails or cracks. Unplug the machine before changing knives or making adjustments. Never wear loose sleeves or gloves near rotating parts. This site gives general information, not professional training, so if you have not used these machines before, learn from a qualified instructor in person.
Deciding whether to buy both
If you rarely build furniture or only use dimensional or surfaced lumber, you probably do not need either one. If you build furniture regularly, use rough lumber, or glue up panels often, the pair opens up a lot, but the combined cost, space, power and dust control needs are significant. Many people start with a planer and a workaround for flattening, then add a jointer later if the work calls for it.