Squaring Rough Lumber: The Four-Square Process

Rough-sawn lumber from a hardwood dealer is cheap relative to S4S (surfaced four sides) because the dealer has not done the milling. The trade-off is that you do the milling. The process is called four-squaring, and it follows a strict order: face, edge, thickness, width. Every step depends on the one before. WHY ORDER MATTERS You cannot make a board parallel to a reference surface that does not yet exist. Each step creates the reference for the next. Doing them out of order — say, planing both faces flat before jointing the first face — produces a smooth board that is not flat. STEP 1: FLAT FACE Use the jointer. Place the board with the cupped face down (concave) so it does not rock on the bed. Take light passes (1/32" maximum) and feed slowly. After two or three passes, look across the board — when the surface no longer has any planer-track shadows or rough patches, the face is flat. If you do not have a jointer, a hand-plane sequence works: scrub plane to remove the high spots, jack plane to flatten, smoothing plane to clean up. Skill required is meaningful; expect to spend 30-60 minutes per board your first few times. STEP 2: SQUARE EDGE Joint one edge against the now-flat face, with the flat face against the jointer fence. Verify the jointer fence is square to the bed — check with a 6" combination square. Even 1° of error here means every joint is off. After two or three light passes, the edge is straight and square to the face. Verify with a square — if there is any light under the square, the fence is off. Fix the fence and re-joint. STEP 3: PARALLEL THICKNESS Run the board through the planer with the jointed (flat) face down. The planer references off the flat face and cuts the opposite face parallel to it. Take 1/32" to 1/16" passes. Flip the board between passes so neither face is heavily cut alone — keeps internal stress balanced. Stop when the rough face is fully planed flat. Mark the final target thickness in pencil; when you reach it, stop. STEP 4: PARALLEL WIDTH Now use the table saw or band saw to rip the second edge parallel to the jointed one. Set the fence and rip the board to about 1/16" over final width. Then take one more pass on the jointer to clean up the saw marks. Or just rip to final width if your saw cuts are clean enough — for utility work, this is fine. The board is now four-square: flat face, parallel opposite face, square edge, parallel opposite edge. GRAIN ORIENTATION DURING MILLING When you joint the first face, orient the board so the milling cuts with the grain. Look at the edge — the grain rises in one direction and falls in the other. Cut downhill, not uphill. Wrong direction causes tearout that takes hours to remove. REST BETWEEN MILLING STEPS If you mill all four sides in 20 minutes, the board may not be flat the next morning. Internal moisture moves to equalize after each cut. Mill all four sides slightly oversize, sticker the boards in your shop for 24-48 hours, then take a final light pass on each side to true up any movement. This step matters most for thick boards (5/4 and up), figured wood, and rough lumber that has been outside or in a damp basement. For dry, straight 4/4 boards, you can often skip the rest period. WORKING WITHOUT A JOINTER A router sled flattens wide boards beyond jointer capacity. A planer with a sled (a flat reference platform under the board) substitutes for a jointer pass. Hand planes are slower but capable. The principle is the same regardless of the tool: one flat face first, then everything else references off it.