What Does a Planer Do? A Complete Guide to Wood Planers, How They Work, and Where They Fit in Your Shop

A wood planer is one of the most useful machines a woodworker can add to a shop, yet its function is frequently misunderstood by beginners. It is not a sander, not a jointer substitute, and not a tool for fixing twisted boards. This guide explains exactly what a planer does, how it works, where it fits in the milling sequence, and what to look for when choosing one.

What a Wood Planer Does: The Core Function

A thickness planer has one primary job: it mills a board so that its two faces are flat, parallel to each other, and at a consistent thickness from one end to the other. That sounds simple, but the practical value is significant. Rough lumber from a sawmill or hardwood dealer arrives with uneven surfaces, varying thickness along the length, and no guarantee that the two faces are parallel. A planer solves all of those problems in a single operation, provided the board enters the machine with one flat reference face already established.

Thicknessing Rough Lumber

The most common use of a wood planer is reducing rough-sawn lumber to a target thickness. When you purchase rough lumber from a sawmill or specialty dealer, you get significantly more material per board foot than with surfaced lumber, at a cost roughly 30 to 50 percent lower than pre-milled stock. A benchtop planer converts that rough stock into usable boards in minutes. You set the machine to cut the board at your desired final thickness, feed the board through, and the planer delivers a smooth, dimensioned face on the top surface.

Creating Two Parallel Faces

A planer does not just smooth a surface. It makes the top face of the board parallel to whatever is resting on the table. This is the second critical function that beginners often overlook. When a board exits a planer, both faces are parallel to each other at a precise thickness. This is what allows joinery to fit properly, panels to glue up flat, and table legs to match in a set. Without parallel faces, a project built from rough lumber will show misalignment at every joint.

What a Planer Cannot Do

A planer cannot flatten a warped, cupped, or twisted board on its own. When a board with a cup or bow is fed through a planer, the feed rollers press the board flat against the table during the cut, but the board springs back to its original shape after it exits. The result is a thinner board that is still warped. To flatten a board with face defects, a jointer or a flat sled in the planer is required first. Once one flat face has been established, the planer uses that face as a reference to make the second face parallel.

How a Thickness Planer Works

Understanding the internal mechanism of a planer explains why it produces the results it does and why proper setup matters. The machine is simpler than it looks from the outside, with three core components doing all the work.

The Feed Rollers and Cutterhead

When a board is pushed toward the infeed side of a planer, the infeed roller grips the board and pulls it through the machine at a controlled speed. The cutterhead, a rotating cylinder fitted with knives or carbide inserts, sits above the table and removes material from the top face of the board as it passes underneath. The outfeed roller then pushes the board out of the machine. Because the board is gripped and driven by the rollers rather than pushed by hand, the feed rate is consistent, which produces a more uniform surface than a handheld tool.

How Depth of Cut Is Set

The distance between the table surface and the lowest point of the cutterhead determines how much material is removed in a single pass. Most benchtop planers allow adjustment in fine increments using a handwheel or crank. Standard practice is to remove no more than 1/16 inch per pass on typical hardwoods and softwoods, and no more than 1/32 inch on very hard or wide boards. Taking too much material in a single pass overloads the motor, increases the risk of tearout, and can stall the machine entirely.

Why a Flat Reference Face Is Required First

The planer uses the bottom face of the board as its reference surface. The table is flat, the rollers hold the board against it, and the cutterhead removes material in a plane parallel to that table. If the bottom face is cupped or bowed, the planer follows that surface and machines the top face to match it rather than correcting it. This is why the standard milling sequence begins with a jointer to establish one flat face, then uses the planer to bring the second face into parallel with it.

Planer vs Jointer: What Each Machine Does

The two machines that beginners most often confuse are the jointer and the planer. They are not interchangeable. They work together in sequence, with each performing tasks the other cannot. The table below maps the key differences.

The jointer comes first in the sequence. It flattens the face and squares one edge, giving the planer a flat reference to work from. Once the planer has the first flat face to register against, it produces a parallel second face and brings the board to final thickness. Together, these two operations produce what is known as S2S (surfaced two sides). Adding a rip cut on the table saw and a crosscut completes the S4S (surfaced four sides) sequence that most furniture and cabinet work requires.

See more: Jointer vs Planer: Key Differences, Which Comes First, and How to Choose

What a Planer Can and Cannot Do

Because a planer is often described simply as a machine that smooths wood, beginners frequently expect it to solve problems it is not designed for. The table below clarifies the boundaries of what a thickness planer actually handles.

The most important limitation to internalize is the first one: a planer cannot fix a warped face. Attempting to use a planer as a substitute for a jointer produces a thinner warped board rather than a flat one. The planer is a thicknessing machine, not a flattening machine, except on boards that already have one flat reference face.

Types of Wood Planers

Wood planers come in three distinct configurations. Each serves a different segment of the market and handles different scales of work. Understanding the differences helps clarify which type is appropriate for a home shop, a mobile job site, or a production environment.

Benchtop Thickness Planer

The benchtop planer, sometimes called a lunchbox planer, is the most common type in home shops. It sits on a workbench or a dedicated stand, accepts boards typically up to 12 or 13 inches wide and 6 inches thick, and removes up to 1/16 inch per pass. Most benchtop models weigh between 50 and 80 pounds, making them portable enough to move if needed. Prices range from around $300 for entry-level machines to $700 or more for models with spiral cutterheads, two-speed feed rates, and snipe-reduction mechanisms. For the vast majority of home shop and small professional shop applications, a 13-inch benchtop planer covers everything a woodworker needs.

Handheld Electric Planer

The handheld electric planer is a compact, portable tool used for light trimming and surface work rather than thicknessing full boards. It is appropriate for tasks like shaving a door edge that has swollen and stuck in its frame, trimming a small amount of material from a glued-up assembly, or easing an edge before finishing. A handheld planer is not a substitute for a benchtop thickness planer: it cannot thickness a board to consistent dimension across its full width, and it requires skill to avoid leaving tracks and ridges on the surface.

Stationary Floor Planer

Stationary planers are industrial machines designed for production environments, cabinet shops, and furniture manufacturers. They accept boards 18 inches wide or more, remove significant material per pass, and run continuously for hours without motor fatigue. They are beyond the requirements and budget of most home shops, but relevant for woodworkers who process large quantities of rough lumber on a regular basis. Floor planers often have helical cutterheads as standard equipment and include automatic feed rate control.

The Cutterhead: How It Affects Surface Quality

The cutterhead is the most performance-critical component of any planer. Two boards fed through different machines at the same settings can come out with dramatically different surface quality depending on the cutterhead design. This is where the choice between straight knives and a spiral cutterhead has the most direct impact on the finished result.

Straight Knife Cutterheads

Straight knife cutterheads use two or three long high-speed steel knives that run the full width of the cutterhead. They are standard equipment on most entry-level and mid-range benchtop planers. The knives cut in a continuous arc across the board width simultaneously, which produces acceptable results on straight-grained wood. On figured, interlocked, or reversing grain, straight knives tend to tear the fibers rather than slice them cleanly. When a knife develops even a minor nick, that nick leaves a visible line running along the full length of every board until the knives are replaced or sharpened.

Straight knife maintenance requires removing each knife, sharpening it, reinstalling it, and setting all knives to exactly the same height. Even small height variation between knives causes vibration and uneven cutting. The process is time-consuming and requires either a dedicated jig or precise technique.

Spiral Cutterheads

A spiral cutterhead replaces the long straight knives with rows of small square carbide inserts arranged in a helical pattern around the cylinder. Each insert engages the wood at a slight skew angle, producing a shearing cut that dramatically reduces tearout on difficult grain. The staggered engagement also lowers the impact load on the machine at any given moment, which reduces noise significantly compared to straight knife machines.

When an insert dulls or chips, it rotates 90 degrees to expose a fresh cutting edge. Each insert has four usable edges. When all four edges are spent, only that individual insert is replaced rather than a full knife set. The result is lower long-term maintenance cost, faster servicing, and consistently better surface quality across all species and grain patterns.

For woodworkers who regularly process figured maple, walnut, cherry, or other woods with complex grain, the difference in surface quality between a straight knife machine and a spiral cutterhead planer is immediately visible and eliminates most of the hand-sanding typically required after planing.

Explore direct-fit spiral cutterheads for your planer: Sheartak Spiral Cutterheads

When You Need a Planer in Your Shop

A planer is not an essential tool for every woodworker, but it becomes practically indispensable once a shop moves beyond pre-dimensioned lumber from a home center. The three situations where a planer pays for itself most quickly are working with rough lumber, processing glue-ups to final thickness, and reclaiming old or salvaged wood.

Rough lumber from a hardwood dealer or local sawmill typically costs 30 to 50 percent less than S4S stock of the same species. A 13-inch benchtop planer, which costs between $300 and $700, pays for itself in lumber savings within a single moderate-sized project if the woodworker is buying rough stock instead of surfaced boards. Beyond cost, rough lumber offers access to species, widths, and thicknesses that are rarely available pre-surfaced, which expands what is possible to build.

Glue-ups are the second major application. When panels are glued from multiple boards, the glued surface is never perfectly flush even with careful preparation. Running a glued panel through the planer after the glue cures produces a flat, smooth surface far more efficiently and accurately than hand tools or sanding.

Reclaimed and salvaged lumber is the third application. Old barn wood, reclaimed flooring, and salvaged beams frequently have enough sound material beneath weathered or painted surfaces to produce beautiful finished boards. After removing any embedded metal fasteners, a planer strips the surface back to clean wood in a few passes.

See more: How to Reduce Planer Snipe with a Spiral Cutterhead

Conclusion

A wood planer thicknesses boards to a consistent dimension and creates two parallel faces from rough or uneven lumber. It works in sequence with a jointer, not as a replacement for one. The cutterhead design determines surface quality more than any other single component, and upgrading from straight knives to a spiral cutterhead is the most impactful improvement available on any existing machine.

See more: What Does a Jointer Do? The Complete Guide for Woodworkers