A jointer is a workshop machine used to make one face of a board flat and one edge straight. It is essential for preparing rough lumber before thickness planing, ripping, or gluing panels. By creating a true reference surface, the jointer helps every later cut become more accurate.
Good jointer technique improves safety, fit, and final build quality in woodworking projects.
The machine works by passing wood over a rotating cutterhead set between an infeed table and an outfeed table. The infeed table is slightly lower than the outfeed table, so the cutter removes a controlled amount of material as the board moves forward. The fence supports the board at a chosen angle, usually 90 degrees for square edges.
A guard covers the exposed cutterhead and should move only as much as needed while the stock passes through.
Understanding Tools & Workshop Machines: Jointer
Rough boards rarely have just one kind of warp. A board can be cupped across its width, bowed along its length, twisted from corner to corner, or crooked along one edge. These problems need different checks.
Place the board on a known flat surface and press each corner. Rocking shows twist or unevenness. Sight along the edge to notice a bow.
Winding sticks, which are two straight matching strips placed across the board at each end, make twist easier to see. Their top edges appear parallel when the board is free of twist.
Mark high spots with pencil before machining. This helps you remove wood only where it is needed and avoids making a board thinner than necessary.
A jointer cuts according to how the board is supported at each moment. At the start of a pass, use firm downward pressure over the infeed side, but do not force a bent board flat with your hands. That pressure can cause the machine to copy the bend rather than remove it.
Once enough of the board has moved past the cutter, shift most downward pressure to the outfeed side. The newly cut area then rides on the reference surface being created. Forward pressure should be steady and directed into the fence during edge work.
If the board moves away from the fence, the edge can lose its square relationship with the face. Several light passes give more control than one deep pass.
Wood grain affects surface quality. Fibres tend to lie in a direction, similar to overlapping scales. Feeding the board in the wrong direction can lift those fibres before they are cut, leaving torn patches called tear-out.
Look at the grain on the board face and feed so the cutter meets the fibres from the lower direction toward the higher direction. Reversing the board often improves a rough cut. Knots, figured grain, and highly irregular grain may still tear even with careful feeding.
Sharp knives or inserts reduce this problem. Dull cutters require more force, leave fuzzy surfaces, and can burnish rather than cleanly cut wood. A smooth surface is useful, but flatness and straightness matter more than a polished appearance.
Good results depend on checking the machine before using it. Resin, dust, or a small chip on a table can tilt the workpiece enough to affect accuracy. The fence must be locked securely because a fence that shifts during a pass creates an edge that is not square.
Never try to joint a piece that is too short to control safely, badly split, full of loose knots, or likely to break apart. Inspect reclaimed wood for nails, screws, and grit, since hidden metal can damage cutters and create dangerous fragments.
Students meet these ideas when making shelves, picture frames, cutting boards, cabinets, and glued panels. In each project, accurate reference surfaces make later measuring, cutting, and assembly much more reliable.
Key Facts
- Depth of cut = outfeed table height - infeed table height, measured as a small positive removal amount.
- A jointer flattens a face or straightens an edge, while a planer makes the opposite face parallel and controls thickness.
- The outfeed table should be level with the highest point of the cutter knives or inserts.
- For edge jointing, the fence is commonly set to 90 degrees so the edge becomes square to the reference face.
- Longer jointer beds help straighten longer boards because they provide more support before and after the cutterhead.
- Safe hand position rule: keep hands above the tables and away from the cutterhead, using push blocks for short, narrow, or thin stock.
Vocabulary
- Infeed table
- The adjustable table before the cutterhead that supports the board and controls the depth of cut.
- Outfeed table
- The table after the cutterhead that supports the freshly cut surface as the board leaves the knives.
- Cutterhead
- The rotating cylinder with knives or carbide inserts that removes wood from the board.
- Fence
- The vertical guide that supports the board during edge jointing and sets the cutting angle.
- Guard
- The spring-loaded cover that shields the cutterhead except where the wood is passing through.
Common Mistakes to Avoid
- Trying to use a jointer to make a board a final thickness is wrong because a jointer creates flat reference surfaces but does not make opposite faces parallel.
- Pressing down hard near the cutterhead is wrong because it can bend a warped board flat during the cut and allow it to spring back afterward.
- Setting the outfeed table too low or too high is wrong because it can cause snipe, taper, rough cuts, or the board to catch as it exits the cutterhead.
- Removing too much material in one pass is wrong because it increases kickback risk, strains the motor, and can leave a rougher surface.
Practice Questions
- 1 A jointer is set so the infeed table is 1.5 mm lower than the outfeed table. If a board makes 4 full passes, what is the ideal total thickness removed from the jointed face?
- 2 A 1.2 m board has a bowed edge that is 6 mm high at the center relative to the ends. If each jointer pass removes about 1 mm from the high spots, about how many passes are needed to remove the bow, assuming careful technique?
- 3 Explain why a woodworker should joint one face flat before using a thickness planer on the opposite face.