What Does a Jointer Do in Woodworking? The Complete Guide to Flat Faces and Square Edges

1. What Is a Jointer?

A jointer is a stationary woodworking machine with one job: to make one face and one edge of a board perfectly flat and square to each other. It does this with a rotating cutterhead mounted between two long, flat tables. You push the board across the tables, the spinning knives shave off a thin layer, and the surface that comes out the far side is truer than the one that went in.

That sounds simple, and in a way it is. But the result is the foundation of everything that follows in a project. Rough lumber from a yard is rarely flat. It cups across its width, bows along its length, and twists like a propeller as it dries. If you build furniture from boards like that, you build the flaws right into the piece, and gaps appear in every joint you cut. If you are brand new to the craft and wondering where this fits, our primer on what woodworking is gives the bigger picture of how the pieces of the hobby connect.

The name is slightly misleading. A jointer does not cut joints like dovetails or mortises. It prepares the wood so that the joints you cut later, and the glue-ups you do, fit tightly. A glue joint between two jointed edges can be nearly invisible, which is where the name comes from: the machine is what lets two boards be “jointed” together into a wide panel. For a tour of the machines and hand tools that do cut the joints themselves, see wood joinery tools explained.

2. What a Jointer Actually Does in the Shop

When people ask what a jointer does, the honest answer is that it does four related things, and each one solves a real problem you will run into the first time you buy rough lumber.

It flattens a face

Run the concave side of a cupped board over the knives with light passes and the high spots disappear first. After several passes the entire face is in a single plane. This is called face jointing, and it is the step that gives you a trustworthy flat reference surface.

It squares an edge

With the flat face held against the jointer fence, which is set at ninety degrees to the tables, you feed the board edge-first. The result is an edge that is straight along its length and square to the face. This is called edge jointing, and it is the second reference surface you need.

It removes bow, crook, and twist

Different kinds of warp have different names. Cup is curvature across the width. Bow is curvature along the length of the face. Crook is curvature along the length of the edge. Twist is when opposite corners sit at different heights. A jointer can correct all of these, although twist and heavy cup take patience and a good technique.

It prepares joints for glue-ups

A freshly jointed edge is smooth, flat, and slightly burnished, which is exactly what a glue line wants. When two such edges meet, the seam closes up with clamping pressure alone. That is how woodworkers build tabletops, panels, and cabinet sides from narrow boards without visible gaps.

Why this matters for the finished project

Consider a simple tabletop glued up from five boards. If each board is slightly bowed, the seams open at the ends or the middle, the clamps pull the panel into a ripple, and the top never sits flat on its base. Now imagine the same boards after jointing. Each seam closes cleanly, the panel stays flat under clamp pressure, and the finished top needs far less sanding to level. The time you spend at the jointer is returned many times over later in the project.

The same logic applies to doors, drawer boxes, and cabinet carcasses. Square stock produces square assemblies. Out-of-square stock produces assemblies that fight you at every step, and you end up fixing the problem with shims, filler, or frustration.

3. Flattening a Board Face: The Jointer’s Signature Move

Face jointing is what most people picture when they think of a jointer, and it is the job that no other common shop machine does as well. A thickness planer, which is often confused with a jointer, will happily make a board uniform in thickness while leaving the cup and twist completely intact. The planer simply presses the board flat against its bed, cuts it, and lets the board spring back. A jointer, in contrast, cuts the high spots first and works down toward a true plane.

How the cut works

The infeed table sits slightly lower than the outfeed table, and the difference between them is your depth of cut. The outfeed table is set exactly level with the top of the knives’ arc. As the board passes the cutterhead, the freshly cut surface rides onto the outfeed table, and that supports the board and guides the rest of the pass. Because the cut surface is always supported by the machine’s flat outfeed table, the finished face ends up flat.

Reading the grain

Grain direction matters. Feed the board so the knives cut with the grain, which means you are looking at the rising or “uphill” grain pattern on the edge of the board as it travels toward the cutterhead. Cutting against the grain tears out chunks and leaves a rough, chipped surface. If you see tear-out, flip the board end for end and try again, or take a lighter pass.

Taking light passes

Most woodworkers keep the depth of cut between one thirty-second and one sixteenth of an inch for face jointing. Thin passes leave a smoother surface, put less stress on the motor, and give you more control over how much material comes off. Heavy cuts invite tear-out and make the board harder to hold steady.

Once one face is flat, mark it with a pencil squiggle or a cabinetmaker’s triangle. That mark tells you which face is your reference, so you do not accidentally joint the wrong side later.

4. Creating a Square Edge for Rips and Glue-Ups

With one flat face established, the next task is a straight, square edge. This is the second half of what a jointer does, and it is just as important as face jointing because it is what makes your table saw cuts safe and accurate.

Why the table saw needs a jointed edge

When you rip a board on the table saw, one edge rides against the fence. If that edge is wavy or bowed, the board rocks, binds against the blade, and can kick back. A jointed edge sits flat on the fence along its whole length. The cut that follows is straight, clean, and predictable. If you are still deciding on a saw to pair with your jointer, our guides on the best table saws for woodworking and how to choose a table saw walk through the options.

The edge jointing technique

Place the flat reference face firmly against the fence, with the edge to be cut down on the table. Feed at a steady pace, keeping the pressure toward the fence over the infeed table at the start, then shifting your pressure over the outfeed table once the board passes the knives. Keep your hands on top of the board and away from the cutterhead, and use push pads as the board’s trailing end approaches.

Why spring joints matter

When gluing up a panel, some woodworkers cut each edge a hair out of square or deliberately create a slightly hollow “spring joint” so the ends close tight and the middle is held by clamp pressure. Because a jointer allows tiny, controlled adjustments, it is the natural tool for these techniques. A good glue-up joint from a jointer is often stronger than the wood fibers on either side.

• Check your fence with a reliable square before each project.
• Mark the jointed face and edge so you always know your references.
• Joint the edges of boards that will be glued together as mating pairs, facing opposite directions, so any slight fence error cancels out.

Checking your fence for square

Set a combination square against the fence and the outfeed table, and look for light between the blade and the fence. If you see a gap, adjust the fence stop. Then test with a scrap board: joint an edge, flip the board so the jointed edge is down on a flat surface, and check it against a square along the face. A fence that is a fraction of a degree off will show up clearly in glue-ups, so a few minutes of calibration pays off.

Edge jointing wide and narrow boards

Narrow boards are easy to run on the fence, but thin and narrow stock can tip. Use a push block that holds the board against the fence as well as down onto the table. Wide boards need the opposite care: keep the face tight to the fence along its full length, because any rocking will produce a slightly curved edge.

5. Anatomy of a Jointer: Understanding Every Part

Before you buy or use one, it helps to know the vocabulary. A jointer looks intimidating at first, but it has only a handful of important parts.

Straight knives versus helical heads

Traditional cutterheads use two or three long straight knives. They cut cleanly when sharp, but they dull from nicks and can be fiddly to set. Helical or spiral cutterheads use many small square carbide inserts arranged in a spiral. Each insert slices at an angle, which dramatically reduces tear-out on figured woods like curly maple. When one insert gets nicked, you rotate it to a fresh edge rather than replacing a whole knife. Helical heads cost more, but many woodworkers consider them the single best upgrade.

Table length matters

Longer tables support longer boards, and longer boards are easier to flatten. A jointer with a table length of around sixty inches or more can handle long stock with less fuss than a small machine. This is one of the clearest differences between a benchtop jointer and a floor-standing model.

If you also own a router or plan to buy one, our overview of top wood router picks pairs well with this one, since routers can chamfer and shape the edges that your jointer has just squared.

Setting and maintaining the knives

On a straight-knife machine, the knives must project exactly the same amount and sit level with the outfeed table at the top of their arc. Magnetic knife-setting jigs make this repeatable. If one knife sits proud, it does all the cutting and leaves ridges. If one sits low, it barely cuts at all. Helical heads avoid this setup step, because each insert seats into a machined pocket and is precisely positioned from the factory.

Keeping the beds clean and waxed

Resin and pitch build up on cast iron tables and create drag, which makes it harder to feed boards smoothly. Wipe the tables clean, then apply a paste wax. A slick bed reduces effort, improves feed consistency, and helps prevent rust in humid shops.

6. Types of Jointers: Which One Fits Your Shop?

Jointers come in several sizes, and the right choice depends mostly on how wide your boards are, how much space you have, and how often you will use the machine.

Benchtop jointers

Benchtop models are compact, relatively affordable, and light enough to move around. Most have six-inch cutting widths and shorter tables. They are a good fit for small garage shops and hobbyists who mostly work with narrow boards.

Stationary (floor-standing) jointers

These are the workhorses. They come in six-, eight-, and larger widths, have longer tables, heavier cast iron beds, and stronger motors. The extra mass dampens vibration, and the long tables make it much easier to flatten long, warped boards. Serious furniture makers usually end up here.

Combination machines

Some machines combine a jointer and planer in one unit, often called a jointer-planer combo. They save space, but they require changeover time, and most have a limited width capacity. They are popular in small European-style workshops.

Parallelogram and long-bed designs

Premium jointers use a parallelogram table design that keeps the infeed and outfeed tables perfectly parallel as you adjust depth. They hold their setting better and stay accurate for years.

Jointers are one of the larger investments in a growing tool collection, so it helps to see them in context. Our roundup of the best woodworking tools shows where a jointer typically falls in a sensible buying order.

7. Jointer vs. Planer: Why You Often Need Both

Beginners often assume a jointer and a planer do the same thing. They do not, and understanding the difference is the key to understanding why the jointer matters.

A jointer creates flat and square surfaces. A thickness planer creates parallel surfaces. The planer works by pressing the board against a flat bed and cutting the top face to match the bed. This means the planer can make the top and bottom faces parallel and the board a uniform thickness, but only after one face has already been made flat. If you feed a cupped board into a planer without jointing first, the board flexes under the feed rollers, gets cut flat while compressed, and springs right back to its cupped shape when it exits.

The classic sequence

The standard milling order goes like this: joint one face flat, joint one edge square to that face, plane the board to thickness with the jointed face down, then rip the board to width on the table saw with the jointed edge against the fence. After that, the saw’s cut edge is already parallel, and the board is dimensionally accurate on all four sides.

Can a planer sled replace a jointer?

Some woodworkers build a planer sled, a flat carrier board with shims that holds a warped board steady while the planer flattens one face. It works for face flattening, but it does not square edges, and it is slower than a jointer. Many people use a sled while they save for a jointer, and that is a perfectly sensible approach.

Once your boards are milled, the next step is usually smoothing the surface. A good random orbital sander takes you from machined faces to a finish-ready surface without much effort.

8. Alternatives to a Jointer: Hand Planes, Sleds, and Router Jigs

A jointer is not the only way to get flat, square stock. Plenty of excellent furniture has been built without one, and if your budget or space is tight, a few alternatives are worth knowing about.

Hand planes

A long jointer plane, typically twenty-two to twenty-four inches, does by hand what the machine does with power. With practice, you can flatten faces and true edges with remarkable accuracy, and you will enjoy a quiet shop with no dust cloud. The trade-off is time and a learning curve. Flattening a wide, twisted board by hand is a real workout. If you are weighing the two approaches in general, our comparison of hand tools vs. power tools for woodworking covers the trade-offs in depth.

Router sleds

A router sled uses a router riding on rails above a board to mill the surface flat. It is slow, but it can handle extremely wide slabs that no jointer can touch. Live-edge tabletop makers rely on this method.

Table saw edge-jointing jig

A simple carrier sled lets you create a straight reference edge on the table saw. Once the edge is straight, the board can ride the fence for ripping the opposite side parallel.

Buying pre-milled lumber

Many lumber suppliers will sell boards that are surfaced on four sides, often labeled S4S. It costs more per board foot, and the wood can still move after you buy it, but it can be a decent starting point for smaller projects.

Combining methods

Plenty of woodworkers mix approaches. They might rough flatten a very wide board with a router sled, then clean it up with a hand plane, and use a jointer only for edges. There is no single correct workflow. What matters is that you end up with surfaces you can trust, and that you understand why each step happens. Once you know what a jointer does, you can recognize the same goals behind every alternative method.

If you do rely on hand tools for flattening, take time to learn to read winding sticks. These two straight sticks, laid across the ends of a board, make twist obvious by exaggerating the difference in height. They are cheap, simple, and useful whether you are using a jointer or a hand plane.

9. How to Choose a Jointer: What to Look For

If you have decided a jointer belongs in your shop, these are the features that separate a satisfying purchase from a frustrating one.

Cutting width

Six inches is the common starting size, and it handles most hardwood boards that come from a lumber yard. Eight-inch machines are a significant step up because they handle wider boards without requiring you to rip them first. If you work with wide stock, the larger width pays off quickly.

Bed length

Longer beds produce flatter results on long boards. As a rule of thumb, aim for a bed at least as long as the boards you commonly mill, though you can work around shorter tables with outfeed support.

Cutterhead type

Helical heads reduce tear-out, are quieter, and last longer between sharpening. Straight knives are cheaper to buy and still work well when kept sharp. If your budget allows, helical is worth the premium.

Fence quality

A fence that stays square and locks solidly is non-negotiable. Look for positive stops at ninety and forty-five degrees and a fence that is long enough to support the board.

Motor power and dust collection

A jointer produces large chips, so a four-inch dust port and a good dust collector are essential. A motor of one horsepower or more gives the cutterhead the torque it needs, especially on dense hardwoods.

Space and budget

Measure your shop honestly. A stationary jointer needs room on both ends for long boards. For help planning your layout, see our guide to setting up a beginner woodshop. If you need to work on job sites or in tight quarters, a portable woodworking workbench can help you build out a flexible setup around a smaller machine.

Questions to ask before you buy

• How wide is the widest board I expect to mill regularly?
• How long are my typical boards, and do I have room for outfeed support?
• Do I have a dust collector, or only a shop vacuum?
• Will I be working mostly with softwoods, domestic hardwoods, or figured exotics?
• Do I already own a planer, or will I need to buy one too?

Honest answers to these questions will steer you toward the right machine far more reliably than a spec sheet will. A jointer that matches your actual projects will feel like a natural part of your shop. One that is too small or too large will feel like a constant compromise.

10. Where the Jointer Fits in a Complete Milling Workflow

Understanding the sequence in which machines are used makes the jointer’s role obvious. Here is the typical path from rough lumber to project-ready stock.

1. Rough cut. Crosscut oversized boards a few inches longer than needed using a miter saw or handsaw. Our guide to the best miter saws for a home shop can help here.
2. Joint a face. Flatten the concave side of each board on the jointer.
3. Joint an edge. Square one edge to the flat face.
4. Plane to thickness. Run the boards through a thickness planer with the jointed face down.
5. Rip to width. Use the table saw with the jointed edge against the fence.
6. Crosscut to final length. Cut the boards to size with a square end.

Let the wood rest

Wood moves as it adjusts to the humidity of your shop. Many woodworkers rough mill their boards, let them rest for a day or two, then take final light passes. This reduces surprises like new warping after a project has been assembled.

Choosing wood that mills well

Straight-grained, well-dried hardwoods mill the most predictably. If you are building a bench from scratch, our guides on the best wood for a woodworking bench and the best plywood for a workbench top cover what to buy and how it behaves under milling.

Dealing with problem boards

Not every board is worth milling. Severe twist, large knots, or boards with internal stress that spring apart when cut can waste hours. When buying lumber, sight down the length of each board like you are looking down a rifle barrel. Pick boards with modest warp and straight grain, and set aside the worst ones for small parts. A little selectivity at the lumber yard saves a lot of work at the jointer.

Plan for waste

Milling removes material. A board that starts at one inch thick may finish at three-quarters of an inch after jointing and planing. Buy extra thickness and length so you can cut around defects and still end up with parts at the dimensions you need.

11. Jointer Safety: Respect the Cutterhead

A jointer is one of the more hazardous machines in a woodshop because the cutterhead is exposed along the width of the table. Safe habits matter, and they are easy to build.

Core safety rules

• Use push blocks. Never pass your hand directly over the cutterhead. Push pads give you grip and keep your hands high and away from the knives.
• Keep the guard working. The spring-loaded guard should swing freely and return fully. Never remove it.
• Do not joint short pieces. Boards shorter than about twelve inches are risky. Use a different method for small parts.
• Feed with the grain. This reduces tear-out and kickback.
• Check for hidden hazards. Nails, screws, and embedded grit can ruin knives or cause injury. Inspect reclaimed lumber carefully.
• Wear eye and ear protection. Jointers are loud and throw chips.
• Use dust collection. Fine dust is a health hazard and chips build up quickly.

Clothing and focus

Remove loose sleeves, jewelry, and anything that could snag. A shop apron with snug fit helps keep fabric out of the way. If you are shopping for one, check out our reviews of the best woodworking aprons. Above all, never use the jointer while tired or distracted. The machine is unforgiving of momentary lapses.

12. Common Jointer Mistakes (and How to Avoid Them)

Even experienced woodworkers fall into a few predictable traps. Knowing them in advance saves wasted lumber and frustration.

Setting the outfeed table incorrectly

If the outfeed table is too low, the end of each pass is cut deeper, a defect known as snipe. If it is too high, the board lifts off the knives and you get a taper. Check the outfeed height with a straightedge whenever you change knives.

Pushing down in the wrong place

Pressure should be on the infeed table at the start of the pass and move to the outfeed table as the board crosses the knives. Pressing down on the overhanging part of a board over the cutterhead causes the board to follow its own curve and defeats the purpose.

Trying to flatten too aggressively

Heavy cuts cause tear-out and leave scalloped marks. Take lighter passes, and be patient on twisted boards.

Ignoring dull knives

Dull knives burnish rather than cut, producing burn marks and rough surfaces. Replace or sharpen them as soon as quality drops.

Skipping the reference marks

Without marks on the jointed face and edge, it is easy to lose track of which surfaces are your references. A quick pencil mark prevents costly mix-ups later.

Buying too small

Many beginners start with a very small machine and outgrow it quickly. Think about the boards you plan to mill over the next few years. And if you are just getting started, our article on how to start woodworking with no experience offers a calm, step-by-step approach to building skills without overspending.

Conclusion: Is a Jointer Worth It?

So, what does a jointer do in woodworking? It gives you flat, straight, square stock, the invisible foundation behind tight joints, flat tabletops, and furniture that stays true over time. It handles the work that planers and table saws cannot do on their own, and it makes every downstream step easier and safer.

If you build projects from rough lumber, a jointer will quickly become one of your most-used machines. If you are just starting out, take your time. Learn the technique with hand planes or a sled, think carefully about the size and type of machine that suits your shop, and invest when the need becomes clear. Whichever route you choose, the goal stays the same: boards that begin flat and square so your work finishes that way.

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