What a planer actually does
A thickness planer makes one face of a board parallel to the other. You feed a board in, and rotating knives or cutters shave the top surface down to the thickness you set. The key point is that a planer references the bottom of the board. If the board is bowed or twisted, the planer’s rollers press it flat while it cuts, and it can spring back afterward with the same bow. For that reason, a planer on its own makes boards uniform in thickness but does not necessarily make them flat. Getting one flat face first is a separate step, which is covered in the article on a planer and jointer working together.
For many projects, uniform thickness is the main thing, and that is where a planer earns its place.
Projects that depend on consistent thickness
Tabletops and panels glued from several boards. When boards of different thickness are glued edge to edge, you get steps between them that have to be sanded away by hand. Planing them to the same thickness first leaves a surface that needs little leveling. This matters for desks, dining tables, benchtops and shelves.
Cutting boards and butcher blocks. Strips glued together in a pattern must be flattened after the glue dries, and the strips themselves need to be uniform to begin with. Many people plane the strips before gluing and plane the finished block lightly to even it out. Check the machine’s minimum board length and thickness in the manual before running short pieces, since small blocks can be unsafe or can damage the machine.
Drawers and boxes. Drawer sides, fronts and backs need to match, and a drawer box with parts of slightly different thickness will not close squarely. Thin stock for drawer sides is often cut from thicker boards and planed down. Matching thickness also helps joints such as dovetails fit cleanly.
Reclaiming rough or weathered lumber. Barn wood, pallet-style boards and older lumber have rough faces. Planing reveals fresh wood below. Check for embedded nails, screws, staples and grit first, because metal can damage knives and cause dangerous kickback. Metal detectors are sometimes used to check reclaimed wood.
Thin stock for small projects. Boxes, inlays, jewelry boxes and models need thinner pieces than lumber yards typically sell. A planer can reduce thickness gradually so you can make your own. Resawing a thick board and planing the halves is a common approach.
Matching existing parts. Repair or replacement work, such as a new drawer front or a replacement shelf, needs wood milled to the dimension of what is already there.
Furniture frames, legs and aprons. Parts that meet in joinery need a consistent thickness so that mortise and tenon joints and similar connections line up. Thickness must be predictable for the joints to fit.
Stair treads, shelves and benchtops from rough-sawn boards. Buying rough lumber is often less expensive per board, though how much you save varies and the planing work, waste and extra tool cost have to be factored in.
Wood movement checks. Boards can move after milling. Taking a little more off after the wood has settled helps final flatness, which is why drying and acclimating lumber before you build is useful.
Planing well
- Remove material in light passes. Taking small cuts reduces tearout and strain on the motor. Check the manual for the maximum recommended cut.
- Watch the grain. Feeding the board so the knives cut with the grain gives a smoother result, and a change in direction can reduce tearout in figured wood. Basic knowledge of wood grain helps you choose the direction.
- Reduce snipe. Snipe is a dip near the ends of a board where the cutterhead shifts as the board enters or leaves. Support long boards at both ends, feed boards end to end in a continuous line, or start with extra length and cut off the ends later.
- Alternate faces on stock that will be reduced a lot. Flipping the board between passes removes material from both sides and reduces the tendency to cup.
- Use dust collection. Planers produce a lot of chips very quickly, and a chip-blocked port can stall the cut. A dust collector or a high-capacity vacuum is generally recommended.
- Keep knives sharp. Dull knives tear grain and leave a rough surface. Replace or sharpen according to the manual.
Choosing between a benchtop planer and a larger stationary machine depends on your space and the width of the boards you plan to use. Benchtop models are common in small shops. A thorough how-to on thickness planing covers the technique in more detail than this list of projects can.
Safety
Wear eye and ear protection, and a dust mask or respirator, because planers are loud and produce a great deal of dust. Stand to the side of the board rather than directly behind it in case of kickback. Never reach into the machine to clear a jam while it is running, and unplug it first. Do not plane boards with loose knots, cracks, nails or damaged ends. Keep loose clothing, jewelry and long hair away from the feed rollers. Follow the manual for your machine, which will list limits on board length, thickness and depth of cut.
Do you need one?
If you buy lumber that is already surfaced on all four sides and your projects use it as is, you may never need a planer. If you want to use rough lumber, make thin stock, match thicknesses or glue up wide panels, a planer opens up options that surfaced lumber cannot provide, and it often becomes a regular part of the shop.