Wood Species and Planing Characteristics

Here's what happens when a plane blade meets wood at the cellular level: the blade edge - measuring perhaps one micron thick - encounters wood cells with walls only 2-5 microns thick. The blade doesn't cut these cells so much as it separates them along natural weak points, shearing through cell walls and rupturing the lignin bonds that hold everything together.

Sometimes this works beautifully. The blade glides through, cells separate cleanly, and you get that glass-smooth surface that feels almost polished. Other times - same plane, same blade, same technique - the wood explodes into tear-out, fibers ripping away in chunks, leaving a surface that looks like it survived a small detonation.

The difference isn't the tool. It's the wood.

Pine planes differently than oak. Maple behaves nothing like cherry. Even within a single species, the board cut from the tree's outer rings acts fundamentally different from the board cut near the heartwood. These aren't subtle variations - they're differences you feel in the resistance of the stroke, see in the surface finish, and hear in the sound the plane makes as it cuts.

Understanding why requires looking at what wood actually is: not a uniform material but a complex cellular structure that varies dramatically between species, between growth conditions, and even within individual boards. The characteristics that make wood useful for construction - its strength, its flexibility, its dimensional stability - all emerge from this cellular architecture. And that same architecture determines exactly how the wood responds when a plane blade tries to cut through it. The blade steel type and heat treatment affects how long the edge stays sharp, but the wood's cellular structure determines the cutting forces that dull it.

Softwood vs Hardwood: Why the Names Mislead

The terms "softwood" and "hardwood" suggest a straightforward hardness distinction. They don't deliver on that promise.

Balsa - one of the lightest, softest woods available - is technically a hardwood. Yew, dense enough to make medieval longbows, is a softwood. The classification has nothing to do with how hard the wood feels and everything to do with botanical ancestry. Softwoods come from gymnosperms (cone-bearing trees like pine, fir, and cedar). Hardwoods come from angiosperms (flowering trees like oak, maple, and cherry).

This botanical distinction creates two fundamentally different cellular structures, and those structures determine planing behavior far more accurately than any measure of hardness.

Softwood Cellular Architecture

Softwoods build their structure primarily from tracheids - elongated cells running parallel to the tree's length, typically 3-5mm long and 20-50 microns in diameter. These cells serve double duty: providing structural support and transporting water. The simplicity shows under magnification. Look at pine or fir end grain and you see a relatively uniform pattern of cells arranged in neat rows.

The cell walls in softwoods contain less lignin than hardwoods - lignin being the polymer that binds cells together and provides rigidity. This lower lignin content means the bonds between cells break more easily under blade pressure. When a plane cuts softwood, it's primarily breaking these relatively weak inter-cellular bonds rather than cutting through cell walls.

This creates the characteristic behavior woodworkers associate with softwood planing: the blade moves through with less resistance, producing continuous shavings that curl smoothly. The lower density means less material for the blade to displace. A typical softwood like pine weighs around 25-30 pounds per cubic foot at 12% moisture content. The blade encounters fewer cells per unit of cutting distance.

But softwoods present their own challenges. The grain patterns in many softwoods alternate between earlywood (formed during spring growth) and latewood (formed during summer). Earlywood cells have thin walls and large voids - they're optimized for rapid water transport during active growth. Latewood cells have thicker walls and smaller voids, providing structural strength.

When a blade transitions from earlywood to latewood within a single stroke, it encounters abrupt density changes. The earlywood compresses easily, almost too easily - the blade can crush cells rather than cutting them cleanly. Then it hits latewood, which resists cutting substantially more. This density variation creates the washboard effect sometimes seen on softwood surfaces, where alternating growth rings show as subtle ridges and valleys.

Hardwood Cellular Complexity

Hardwoods construct themselves from multiple cell types working in specialized roles. Fibers provide structural support. Vessels transport water. Parenchyma cells store nutrients. This division of labor creates more complex grain patterns and more variable planing behavior.

The vessels in hardwoods - particularly in ring-porous species like oak and ash - can measure 200-400 microns in diameter, ten times larger than softwood tracheids. These vessels appear as visible pores in the end grain. In ring-porous hardwoods, large vessels concentrate in the earlywood, creating distinct bands. In diffuse-porous hardwoods like maple and cherry, smaller vessels distribute more evenly throughout the growth rings.

Those large vessels create discontinuities in the wood structure. A plane blade cutting across oak encounters fiber cells, then suddenly hits a vessel - essentially a hollow tube in the wood matrix. The blade must cut around these vessels or through their walls, depending on cutting direction. This contributes to oak's tendency toward rougher planing surfaces compared to diffuse-porous species.

The higher lignin content in hardwoods creates stronger bonds between cells. When the blade cuts hardwood, it does more actual cell-wall cutting and less inter-cellular separation than in softwoods. This shows up as increased cutting resistance. Maple at 44 pounds per cubic foot contains substantially more material per unit volume than pine, and that material is more strongly bonded together.

But hardwoods reward this extra effort with superior surface finish potential. The smaller, more uniform cells in diffuse-porous hardwoods like maple allow planes to achieve surfaces that appear almost polished. The cell structure simply contains fewer large discontinuities where tear-out can initiate.

The Density Spectrum

Actual hardness and density vary across a spectrum that ignores the softwood/hardwood classification. Among softwoods, Douglas fir weighs around 33 pounds per cubic foot - denser than some hardwoods. Southern yellow pine approaches 40 pounds per cubic foot in some varieties. Among hardwoods, basswood weighs just 26 pounds per cubic foot, lighter than many softwoods.

This density directly affects planing resistance. The cutting force required scales roughly with wood density. Plane a board of 25-pound-per-cubic-foot basswood, then plane a board of 45-pound-per-cubic-foot hard maple. The difference in resistance is immediate and obvious - the maple requires nearly twice the force to advance the plane at comparable depths of cut.

Density also correlates with edge dulling rates. Denser woods contain more material for the blade to cut through per unit of travel. That 45-pound maple board presents 80% more wood substance to the blade than the 25-pound basswood board over identical planing distances. The blade edge experiences correspondingly more wear.

Grain Direction: The Single Most Critical Factor

Wood grain isn't decorative pattern - it's the visual manifestation of how cells align in the tree. Those cells grow vertically in the living tree, creating long parallel tubes running from roots to crown. When lumber gets cut from the log, those cell orientations determine grain direction in the finished board.

The relationship between grain direction and planing direction creates the fundamental rule of wood behavior: cells want to separate along their length, not across it. A plane blade cutting with the grain direction - following the cell alignment - produces clean separation. The same blade cutting against the grain tries to force cells apart the hard way, often lifting fibers away from the surface before cutting them.

Reading Grain Direction

Grain direction reveals itself through several visual cues. The most obvious appears on edge grain: look at a board's edge and you'll see lines representing growth rings. These lines angle across the board thickness, and that angle indicates grain direction on the face.

If the lines angle upward from left to right on the edge, the grain "rises" in that direction on the face. Planing from left to right follows the grain down. Planing from right to left goes against it, climbing up the grain like trying to pet a cat backwards.

Face grain patterns provide additional information. In flat-sawn boards where annual rings run roughly parallel to the face, the cathedral patterns show grain direction. The "point" of each cathedral indicates the direction fibers are heading. Planing toward these points generally works with the grain. Planing away from them fights it.

But grain rarely runs perfectly straight for any distance. Trees grow in spirals. Branches create disturbances. Reaction wood forms on the compression side of leaning trunks. All these factors create grain that wanders, reverses, and interlocks in ways that make consistent planing direction impossible across an entire board.

With the Grain: The Ideal Condition

When blade direction aligns with grain direction, the cutting action works with wood's natural structure. The blade encounters cell ends rather than cell sides. As the blade advances, it splits cells along their length - the direction they separate most easily.

This produces what woodworkers describe as "planing like butter." The blade glides through with minimal resistance. Shavings emerge as continuous ribbons rather than broken chips. The surface left behind shows no torn fibers, no fuzzy patches, no raised grain. Under magnification, the surface reveals cleanly cut cell ends lined up like the bristles of a brush.

The cutting forces in with-the-grain planing act primarily in shear along the cell length. Wood is weakest in this direction - cells separate along their length at roughly one-tenth the force required to break them across their width. A blade aligned with grain direction exploits this weakness.

Even difficult woods behave well when planed with the grain. Figured maple, notorious for tear-out, produces clean surfaces if the grain direction happens to align favorably. The figure itself - the wavy, curly patterns - represents grain that deviates from straight, but there are still local directions where cutting works with rather than against the structure.

Against the Grain: When Structure Fights Back

Reverse the planing direction and everything changes. The blade now encounters cell sides rather than cell ends. As it advances, the blade tries to lift cells away from their neighbors before cutting them. This lifting action works against the lignin bonds holding cells together.

In best cases, this produces fuzzy surfaces where fibers pull up slightly before cutting, leaving small raised areas. In worst cases - particularly in woods with interlocked grain or figure - entire chunks of wood lift away ahead of the blade, creating the characteristic "tear-out" that ruins surface finish.

The mechanism becomes clear under slow-motion observation. The blade enters the wood and begins compressing cells ahead of it. In with-grain cutting, this compression stays ahead of the cutting edge and gets severed before it propagates far. In against-grain cutting, the compression follows cell alignment away from the surface, deeper into the wood. Eventually these compression forces exceed the wood's tensile strength perpendicular to grain, and chunks tear away below the intended cutting depth.

The severity depends on multiple factors. Dense hardwoods with strong inter-cellular bonds resist tear-out better than softwoods with weaker bonds. Woods with high lignin content hold together more tenaciously. But even dense hardwoods tear out if grain angles and blade angles combine unfavorably.

Interlocked and Reversing Grain

Many tropical hardwoods exhibit interlocked grain, where cell direction spirals around the tree's length, reversing direction every few growth rings. Species like sapele, ribbon mahogany, and many African hardwoods show this pattern. When boards are cut from these trees, the grain appears to reverse direction every few inches across the board width.

This creates impossible planing conditions. No single planing direction works with the grain across the entire surface. Plane left to right and half the board planes cleanly while the other half tears out. Reverse direction and the problem inverts - the previously clean areas now tear while the torn areas smooth out.

Figured woods create similar challenges through different mechanisms. Curly maple, quilted maple, bird's-eye maple - all these patterns represent grain that deviates from straight in complex three-dimensional curves. The grain direction changes not just across the board but through its thickness. A blade might start cutting with the grain, then encounter a grain reversal mid-stroke as cell orientation shifts.

These grain patterns explain why some woods develop reputations as difficult to plane. The difficulty isn't in the wood's hardness or density - it's in the grain geometry that makes clean cutting direction impossible to maintain.

End Grain: A Special Challenge

Cutting across cell ends - true end grain planing - presents entirely different conditions than face grain work. The blade must sever cells across their width, cutting through cell walls rather than separating cells lengthwise.

This requires substantially more force. Cell walls, though thin, are remarkably strong across their width. The blade must simultaneously cut through thousands of cell walls per square millimeter of cutting surface. In softwoods with thin-walled cells, this remains feasible. In dense hardwoods with thick-walled cells, end grain planing can require cutting forces several times higher than face grain work.

The severed cells also behave differently. Face grain planing produces shavings as connected fibers lift away. End grain planing produces dust-like particles as individual cell fragments separate. The surface left behind shows the open ends of cells - visible pores in hardwoods, less obvious in softwoods but still present under magnification.

End grain surfaces also dull blades much faster than face grain. Each stroke contacts more cell wall material per unit of blade travel. The cumulative effect shortens edge life substantially - end grain work might dull a blade in one-quarter the time face grain work requires.

Common Species: Specific Planing Characteristics

The cellular principles outlined above manifest differently across wood species. Each species evolved its structure to solve specific environmental challenges - drought resistance, mechanical strength, rapid growth - and those evolutionary solutions create distinct planing behaviors.

Pine (Pinus Species)

Pine represents the archetypal softwood planing experience. The wood's low density - typically 25-35 pounds per cubic foot depending on species - means the blade encounters relatively few cells per cutting stroke. The cell walls contain modest lignin levels, creating weak inter-cellular bonds that separate easily.

This produces low cutting resistance. Pine planes with minimal physical effort compared to denser woods. Shavings emerge as continuous curls that compress easily due to the wood's softness. The surface finish potential, however, remains limited by the wood's structure.

The dramatic difference between earlywood and latewood in pine creates visible banding. Earlywood cells, optimized for water transport, have walls so thin they collapse under blade pressure rather than cutting cleanly. This produces slightly crushed areas that appear duller than the surrounding wood. Latewood cuts more cleanly but stands slightly proud of the compressed earlywood, creating subtle ridges.

Pine's resin content adds another variable. The resin exists in specialized cells called resin canals, typically 100-200 microns in diameter. When the blade cuts through resin canals, liquid resin releases and can accumulate on the blade edge, effectively gumming up the cutting geometry. This happens more in species like white pine with high resin content, less in species like ponderosa pine with lower resin concentrations.

The softness that makes pine easy to cut also makes it vulnerable to surface compression. Even sharp blades can burnish rather than cut if angles aren't favorable, creating shiny compressed areas rather than clean cuts. This burnishing becomes more pronounced as blades dull.

Oak (Quercus Species)

Oak's ring-porous structure creates some of the most challenging conditions in common hardwoods. The large earlywood vessels - often 300-400 microns in diameter - appear as obvious holes in the end grain. These vessels create discontinuities that the blade must navigate around or through.

When cutting across these vessels, the blade essentially encounters void spaces. The vessel walls themselves are thin relative to the vessel diameter, and they often don't cut cleanly, instead crushing or tearing. This contributes to oak's reputation for producing somewhat coarse surfaces even with sharp tools.

The wood surrounding the vessels - composed of thick-walled fiber cells - cuts cleanly enough, but the density variations between vessel areas and fiber areas create resistance changes within individual cutting strokes. The blade might move easily through vessel-rich earlywood, then bog down in the dense latewood fiber regions.

Oak's high tannin content - up to 10% by weight in some species - affects edge longevity. Tannins are acidic compounds that can corrode steel, particularly tool steels that lack high chromium content. An O1 blade cutting oak shows accelerated dulling compared to the same blade in maple, partially from mechanical wear but also from chemical interaction.

The ray cells in oak - visible as "flecks" in quartersawn boards - cut with different properties than the surrounding fiber cells. Ray cells run radially from the tree's center outward, perpendicular to the main grain direction. When the blade encounters these rays, it's effectively cutting cross-grain even when planing with the main grain direction. This creates small areas of slightly rougher texture where rays intersect the surface.

Maple (Acer Species)

Hard maple's diffuse-porous structure distributes vessels evenly throughout the wood rather than concentrating them in growth ring bands. These vessels measure 50-100 microns - substantially smaller than oak's vessels - creating a more uniform cellular matrix.

This uniformity translates to excellent planing characteristics when grain cooperates. The density at 44 pounds per cubic foot means substantial cutting resistance, but that resistance stays consistent throughout the stroke. No sudden transitions from soft to hard zones. The blade encounters essentially the same material density throughout its travel.

The small, evenly distributed pores allow maple to achieve surface finishes that approach polished appearance. Under magnification, a well-planed maple surface shows cleanly cut cell ends in remarkably uniform arrangement. The tiny pores simply don't create the discontinuities that rough up oak surfaces.

But maple's figure - curly, quilted, bird's-eye, or spalted patterns - represents grain deviation that creates tear-out problems. Curly maple, where growth rings form waves rather than straight lines, presents continuously reversing grain. The blade alternates between cutting with and against grain within millimeters of travel, making clean surfaces difficult regardless of planing direction.

Bird's-eye maple, caused by adventitious buds that never developed into branches, contains localized grain distortions around each "eye." The grain swirls in complex three-dimensional patterns around these features. Planing across bird's-eyes almost inevitably produces some tear-out as grain direction becomes impossible to follow consistently.

Spalted maple adds another complexity - the black zone lines created by fungal activity actually represent boundaries where the wood's cellular structure has been partially degraded. These zones cut differently than surrounding wood, sometimes more easily (if degraded enough) or less cleanly (if the fungal compounds have hardened the cells).

Cherry (Prunus Species)

Black cherry combines moderate density (35 pounds per cubic foot) with diffuse-porous structure and relatively straight grain. This combination produces some of the most pleasant planing experiences in common hardwoods.

The wood's cellular structure lacks dramatic density variations. Vessels distribute evenly and measure 75-100 microns - large enough to provide efficient water transport but small enough to avoid the discontinuities that plague ring-porous species. The fiber cells show consistent wall thickness throughout growth rings.

This consistency means cherry planes with steady resistance that neither bogs down in hard zones nor crushes in soft zones. The blade advances smoothly, producing shavings that curl evenly. Surface finish potential rivals maple but requires less effort to achieve because grain typically runs straighter in cherry than in figured maple.

Cherry's gum deposits - natural compounds the tree produces - occasionally create problems. These gum pockets appear as dark streaks or spots in the wood. The gum itself is substantially harder than surrounding wood and can dull blades faster than clean cherry. When the blade encounters gum deposits, cutting resistance increases abruptly and the gum can adhere to the blade edge.

The wood's color variation - from pale sapwood to rich reddish-brown heartwood - represents different cell wall chemistry but doesn't significantly affect planing behavior. The cellular structure remains consistent across color transitions.

Walnut (Juglans Species)

Black walnut's semi-ring-porous structure places it between oak's dramatic ring porosity and maple's diffuse porosity. Earlywood vessels measure 150-200 microns - larger than maple but smaller than oak. These vessels concentrate somewhat in growth ring boundaries but not as exclusively as in oak.

The resulting planing characteristics split the difference between oak's coarseness and maple's refinement. Walnut produces cleaner surfaces than oak because vessels don't dominate the structure as completely. But it doesn't quite match maple's potential for glass-smooth finishes because those moderately large vessels still create some texture.

Density at 38 pounds per cubic foot makes walnut slightly less demanding to plane than maple but noticeably more resistant than cherry. The chocolate brown color comes from natural compounds in the cell walls - compounds that don't significantly affect planing mechanics but do create distinctive dust that stains light-colored adjacent woods if shavings mix.

Walnut's grain typically runs fairly straight, reducing tear-out compared to figured woods. When figure does occur - crotch figure, burls, or curl - it creates the same grain reversal problems that affect other species. But straight-grained walnut planes predictably, rewarding proper grain direction with clean surfaces.

Douglas Fir (Pseudotsuga Menziesii)

Douglas fir challenges the assumption that softwoods plane easily. At 33 pounds per cubic foot, it's denser than many hardwoods. The pronounced difference between earlywood and latewood creates some of the most dramatic density variations in common lumber.

Earlywood bands - formed during rapid spring growth - contain thin-walled cells that compress easily. Latewood bands - summer growth - develop thick-walled cells approaching hardwood density. When the blade transitions from earlywood to latewood, the resistance change feels like hitting different materials entirely.

This creates the washboard effect more severely in Douglas fir than in most softwoods. The latewood cuts cleanly and stands slightly proud. The earlywood compresses before cutting, creating subtle valleys. The resulting surface shows visible banding that remains even after thorough planing.

The wood's resin content varies by tree age and growing conditions. Older, slower-growing trees contain more resin than young plantation-grown material. Resin accumulation on blades happens frequently enough to require regular cleaning during extended planing sessions.

Douglas fir grain typically runs straight in clear, vertical-grain lumber. But the material commonly available often contains knots - areas where branches grew from the trunk. Knots represent grain running perpendicular to the main trunk grain, creating localized areas of extreme grain deviation. These knots are also substantially denser than surrounding wood and dull blades faster.

Mahogany (Swietenia and Khaya Species)

True mahogany (Swietenia) and African mahogany (Khaya) share structural characteristics that make them remarkably pleasant to plane despite moderate density. Both show diffuse-porous structure with small, evenly distributed vessels. Density runs 31-37 pounds per cubic foot depending on species and growing conditions.

The cellular matrix shows unusual uniformity - growth rings remain visible but don't create pronounced density variations. The transition from earlywood to latewood happens gradually rather than abruptly. This means cutting resistance stays essentially constant throughout blade travel.

The result: mahogany planes with smooth, steady resistance that many woodworkers describe as the most pleasant of any wood. The blade glides through without sudden catches or resistance changes. Shavings curl uniformly. Surface finish potential is excellent, though not quite matching hard maple's ultimate refinement.

However, many mahogany species exhibit interlocked grain to varying degrees. The grain spirals around the trunk, reversing direction every few growth rings. When lumber is cut from these logs, the grain appears to reverse every few inches across the board width. This creates ribbon-stripe figure in quartersawn boards - visually attractive but challenging to plane.

With interlocked grain, no single planing direction works across the entire surface. Areas that plane cleanly in one direction tear out when adjacent areas with reversed grain are cutting against direction. This makes figured mahogany substantially more challenging than straight-grained material despite identical cellular structure.

Moisture Content and Seasonal Behavior

Wood isn't stable material. It absorbs moisture from humid air and releases it to dry air, constantly seeking equilibrium with surrounding conditions. This moisture movement fundamentally alters cellular structure and consequently changes planing behavior.

The Hygroscopic Nature of Wood

Wood cells evolved to transport water in living trees. Even after cutting and drying, those cells retain their ability to absorb and release moisture through their cell walls. The cell wall structure - composed of cellulose fibers held in a matrix of hemicellulose and lignin - contains hydroxyl groups that bond with water molecules.

This creates what wood scientists call hygroscopic behavior. Wood at 0% moisture content exposed to 50% relative humidity will absorb moisture until reaching approximately 9% moisture content. The same wood at 30% moisture content in 30% relative humidity will release moisture until dropping to about 6%. This equilibrium moisture content varies with temperature and humidity but always tends toward balance with surrounding conditions.

The practical result: wood stored in a heated winter workshop at 30% relative humidity measures 6-7% moisture content. The same wood moved to a summer garage at 70% relative humidity rises to 12-14% moisture content over several weeks. This represents a moisture change that significantly affects cellular dimensions and mechanical properties.

How Moisture Affects Cell Structure

Water molecules enter wood cell walls and push apart the cellulose fibers, causing the cells to swell. This swelling happens primarily in the radial and tangential directions - across the grain - rather than along the grain. A board 6 inches wide at 6% moisture content might measure 6.25 inches wide at 12% moisture content, representing over 4% dimensional change.

But the swelling isn't uniform across cell types. Earlywood cells with thin walls swell proportionally more than latewood cells with thick walls. This creates internal stresses as different parts of the wood structure expand at different rates. In extreme cases, these stresses produce checking - small cracks that relieve stress but compromise the wood's integrity.

The swollen cells also exhibit different mechanical properties. The water molecules that push cellulose fibers apart also lubricate movement between those fibers. This makes wet wood softer and more compressible than dry wood. A blade pressing into wood at 12% moisture compresses cells more easily than the same blade in wood at 6% moisture.

Planing Green vs. Dry Wood

Freshly cut "green" wood contains moisture far above equilibrium levels - often 40-80% moisture content in sapwood, 30-50% in heartwood. At these moisture levels, cell walls are fully saturated and free water fills cell cavities.

Green wood planes very differently than dry wood. The high moisture content makes the wood dramatically softer. Blade resistance decreases substantially - green oak might plane as easily as dry pine. But this ease of cutting comes with compromises.

The compressed, wet cells don't spring back after cutting. They remain compressed, creating a surface that feels smooth immediately after planing but becomes fuzzy as the wood dries and cells attempt to recover their shape. The water also prevents clean shaving formation. Instead of producing crisp shavings that curl smoothly, green wood produces damp, limp shavings that compress into masses rather than individual ribbons.

As green wood dries to equilibrium moisture content, it shrinks substantially. A board planed flat when green develops cupping, twisting, or warping as moisture leaves and cells contract unevenly. This makes planing green wood impractical for any work requiring dimensional stability.

The 6-8% Moisture Window

Wood destined for interior use typically equilibrates at 6-8% moisture content, matching typical heated interior environments. Wood at this moisture level exhibits optimal planing characteristics for most species.

The cells contain enough moisture to maintain flexibility - they don't become brittle as they would at extremely low moisture levels. But they contain little enough moisture that cellular structure remains firm rather than spongy. Blade edges cut cleanly without excessive compression. Shavings form as distinct ribbons that curl predictably.

Surface finish quality peaks in this moisture range. The cells cut cleanly and stay cut rather than compressing and recovering later. The wood's dimensional stability means surfaces planed flat remain flat as long as humidity stays constant.

Seasonal Movement and Planing Behavior

Real workshops experience seasonal humidity swings that move wood moisture content through several percentage points annually. A board at 6% moisture in January might reach 11% by August in many climates. This 5-point swing represents approximately 3% dimensional change across the grain.

This movement affects planing in subtle ways. Wood at 11% moisture compresses slightly more under blade pressure than the same wood at 6%. This increased compression can create surfaces that appear smooth immediately after planing but develop slight fuzziness as the wood dries and compressed fibers spring back.

The phenomenon becomes particularly noticeable in softwoods with thin-walled cells. Pine planed at 11% moisture often develops raised grain as it dries to 7% - the compressed earlywood cells recover enough to project above the cutting plane. The same pine planed at 7% moisture stays smooth because cells weren't compressed beyond their elastic limit.

Dense hardwoods with thick-walled cells show less susceptibility to this effect. Maple at 11% moisture cuts nearly as cleanly as maple at 7% because the thick cell walls resist compression even when moisture-softened.

Frozen Wood: An Extreme Case

Wood at temperatures below freezing - particularly wood with elevated moisture content - exhibits dramatically different planing behavior. The water in cell walls and cavities freezes, effectively turning the wood into a composite material of wood fibers and ice crystals.

Frozen wood becomes substantially harder and more brittle. Cutting forces increase significantly - frozen oak might require twice the force of room-temperature oak. But the brittleness that makes frozen wood harder also makes it more prone to chipping and splintering. Cells fracture rather than cutting cleanly.

The ice content also dulls blades faster. Ice crystals act as abrasive particles that wear blade edges. A blade might maintain acceptable sharpness for several hours of planing room-temperature wood but dull noticeably after thirty minutes in frozen wood.

Case Hardening and Surface Checking

Improperly dried lumber sometimes develops case hardening - a condition where the outer layers dry and shrink while the core remains wet. This creates internal stresses that persist even after the wood reaches uniform moisture content. Case-hardened wood planes poorly because the stressed surface layers respond unpredictably to cutting forces, sometimes splintering or checking as stress releases.

Surface checking - fine cracks that develop perpendicular to grain - affects planing by creating discontinuities where the blade catches. Even shallow checks that barely register visually can cause small tear-outs as the blade crosses them. The blade enters the check, drops slightly, then climbs back to the surface level, often lifting fibers in the process.