andrewlb notes

Understanding Wood

Understanding Wood

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Highlights

  • Wood comes from trees. This is the most important fact to remember in understanding the nature of wood. Whatever qualities or shortcomings wood possesses are traceable to the tree whence it came. Wood evolved as a functional tissue of plants and not as a material designed to satisfy the needs of woodworkers. (Location 411)
  • The bark might actually have to be carved off if the tree is cut during the dormant season. (Location 483)
  • the term figure is used to refer to distinctive or characteristic markings on longitudinal or side-grain surfaces of wood. (Location 971)
  • The term moonshine crotch is also applied to crotch figure. (Location 1014)
  • Large, closely crowded bulges in the growth layers produce blister figure (Figure 2.20), which is also called quilted figure (Figure 2.21) if the mounds are elongated. When finished smoothly, the variation in light reflectiveness because of grain distortion creates a very unusual three-dimensional effect, so that the figure seems to roll when the piece is moved. Quilted and blister figures are usually associated with bigleaf maple but are occasionally formed in other species as well. (Location 1067)
  • Knots are simply the parts of limbs that are embedded in the main stem of the tree (Location 1110)
  • If compression were the only factor, a 250-lb. person could be supported by four hickory dowels, each one only ⅛ in. dia. We see this in the formula: (Location 2151)
  • Compression perpendicular to the grain is very often a limiting strength. Go back to our example of the hickory chair with legs tapered to ⅛ in. Although the 5,102 psi developed at the tips could be carried by the chair legs, it would easily punch into the surface of an eastern white pine floor board whose FSPL is listed at only 440 lb. In fact, a 120-lb. woman placing her full weight on a shoe with a ½-in. by ½-in. heel will develop a stress as high as: Eastern white pine obviously is not a logical choice for flooring, but the 2,170-psi perpendicular-to-grain strength of hickory would comfortably resist heel denting. (Location 2177)
  • The two most relevant questions facing the woodworker are how much the beam will carry and what factors influence its carrying capacity, as well as how much the beam will deflect and what factors influence its deflection. (Location 2402)
  • The study of time-dependent stress and strain behavior is called rheology. (Location 2568)
  • Visual determination of grain direction can be most deceiving. Except on true radial surfaces, the temptation to use growth rings as an indicator of grain direction should be avoided. Except on tangential surfaces, rays also should not be relied upon. Linear anatomical features visible to the eye, such as softwood resin canals or hardwood vessels, are quite helpful. It may also help to mark the wood with ink or dye using a felt-tipped pen. The grain direction then will be indicated by hairline extensions of the ink along longitudinal elements. (Location 2592)
  • In judging the strength of a piece of knotty lumber, imagine all the knots cut away, then ask yourself whether what is left will be strong enough. (Location 2654)
  • When the bole of a tree is bent like a giant beam, the wood in the concave side can fail in compression without tension failure developing in the convex side. Thus, the compression damage to the tree might go unnoticed. The result is irregular planes of buckled longitudinal cells, called compression failures, which generally run crosswise to the grain. In rough lumber they are virtually impossible to detect, but on planed or sanded longitudinal surfaces, they are usually visible, appearing as wrinkles across the grain (Location 2681)
  • Critical structural members, such as ladder rails, scaffolding, aircraft parts, and boat spars, must be carefully inspected to exclude material with compression failures. Wood containing compression failures is also unsuitable for steam-bending work. (Location 2690)
  • it clear that wood is a better thermal insulator than most other structural materials. It is more than seven times more effective than concrete, 300 times more effective than steel, and 1,400 times more effective than aluminum of comparable thickness. (Location 2838)
  • Wood has values or powers that cannot be quantified in scientific terms. These aspects of wood, without being well-understood or even explainable, may well be among the most important and powerful. However difficult they are to describe or define, we can at least demonstrate their certain existence. (Location 3037)
  • When this balance of moisture exchange is established, the amount of bound water eventually contained in a piece of wood is called the equilibrium moisture content (EMC) of the wood. The relationship between the amount of bound water in wood and the RH is shown in Figure 6.3. In my estimation, this is the most important item in this book. (Location 3171)
  • Figure 6.3 • This may be the most important information in this book. Hang a copy of this graph on your shop wall and look at it every day. The amount of bound water in wood is determined by the relative humidity (RH) of the surrounding atmosphere; the amount of bound water changes as the RH changes. The moisture content of the wood when a balance is established at a given RH is its equilibrium moisture content (EMC). The solid line on the graph represents the relationship between EMC and RH for white spruce, a typical species with a fiber saturation point (FSP) of about 30% EMC. It is a fair approximation of the relationship for most common woods. (Location 3179)
  • cold. It is important to realize that if the absolute humidity of air is unchanged, lowering the temperature of the air raises the RH, while heating the air lowers the RH. (Location 3213)
  • thinking of an equilibrium relative humidity (ERH) rather than an EMC to emphasize the fact that RH determines EMC, not the other way around. It is prudent to think that “my lumber should be at equilibrium with 40% relative humidity” rather than that “my lumber should be at 7.5% moisture content.” (Location 3233)
  • Figure 6.9 • Freshly cut 10-in.-wide red oak planks on a workbench top would shrink as the wood dried, leaving cracks. where ΔD = change in dimension due to shrinkage (Location 3741)
  • It somehow seems absurd that although men have walked on the moon and heart transplants succeed, we still have wobbly chairs. (Location 4008)
  • When contemplating problems such as internal/external joints where restrained swelling is likely, remember that the elastic limit of wood under compression perpendicular to the grain is on average less than 1%, so that restrained swelling of the magnitude of 1% may be setting up a problem. (Location 4037)
  • If bowls are green-turned to wall thicknesses of ½ in. to ⅝ in., a wood with average density such as black walnut can be treated with a moderate schedule (e.g., three weeks at 70°F in a 30% PEG solution or one week at 140°F in a 50% solution) to achieve a high degree of stabilization. (Location 4317)

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title: Understanding Wood longtitle: Understanding Wood author: R. Bruce Hoadley url: , source: kindle last_highlight: 2018-04-25 type: books tags:

Understanding Wood

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Metadata

Highlights

  • Wood comes from trees. This is the most important fact to remember in understanding the nature of wood. Whatever qualities or shortcomings wood possesses are traceable to the tree whence it came. Wood evolved as a functional tissue of plants and not as a material designed to satisfy the needs of woodworkers. (Location 411)
  • The bark might actually have to be carved off if the tree is cut during the dormant season. (Location 483)
  • the term figure is used to refer to distinctive or characteristic markings on longitudinal or side-grain surfaces of wood. (Location 971)
  • The term moonshine crotch is also applied to crotch figure. (Location 1014)
  • Large, closely crowded bulges in the growth layers produce blister figure (Figure 2.20), which is also called quilted figure (Figure 2.21) if the mounds are elongated. When finished smoothly, the variation in light reflectiveness because of grain distortion creates a very unusual three-dimensional effect, so that the figure seems to roll when the piece is moved. Quilted and blister figures are usually associated with bigleaf maple but are occasionally formed in other species as well. (Location 1067)
  • Knots are simply the parts of limbs that are embedded in the main stem of the tree (Location 1110)
  • If compression were the only factor, a 250-lb. person could be supported by four hickory dowels, each one only ⅛ in. dia. We see this in the formula: (Location 2151)
  • Compression perpendicular to the grain is very often a limiting strength. Go back to our example of the hickory chair with legs tapered to ⅛ in. Although the 5,102 psi developed at the tips could be carried by the chair legs, it would easily punch into the surface of an eastern white pine floor board whose FSPL is listed at only 440 lb. In fact, a 120-lb. woman placing her full weight on a shoe with a ½-in. by ½-in. heel will develop a stress as high as: Eastern white pine obviously is not a logical choice for flooring, but the 2,170-psi perpendicular-to-grain strength of hickory would comfortably resist heel denting. (Location 2177)
  • The two most relevant questions facing the woodworker are how much the beam will carry and what factors influence its carrying capacity, as well as how much the beam will deflect and what factors influence its deflection. (Location 2402)
  • The study of time-dependent stress and strain behavior is called rheology. (Location 2568)
  • Visual determination of grain direction can be most deceiving. Except on true radial surfaces, the temptation to use growth rings as an indicator of grain direction should be avoided. Except on tangential surfaces, rays also should not be relied upon. Linear anatomical features visible to the eye, such as softwood resin canals or hardwood vessels, are quite helpful. It may also help to mark the wood with ink or dye using a felt-tipped pen. The grain direction then will be indicated by hairline extensions of the ink along longitudinal elements. (Location 2592)
  • In judging the strength of a piece of knotty lumber, imagine all the knots cut away, then ask yourself whether what is left will be strong enough. (Location 2654)
  • When the bole of a tree is bent like a giant beam, the wood in the concave side can fail in compression without tension failure developing in the convex side. Thus, the compression damage to the tree might go unnoticed. The result is irregular planes of buckled longitudinal cells, called compression failures, which generally run crosswise to the grain. In rough lumber they are virtually impossible to detect, but on planed or sanded longitudinal surfaces, they are usually visible, appearing as wrinkles across the grain (Location 2681)
  • Critical structural members, such as ladder rails, scaffolding, aircraft parts, and boat spars, must be carefully inspected to exclude material with compression failures. Wood containing compression failures is also unsuitable for steam-bending work. (Location 2690)
  • it clear that wood is a better thermal insulator than most other structural materials. It is more than seven times more effective than concrete, 300 times more effective than steel, and 1,400 times more effective than aluminum of comparable thickness. (Location 2838)
  • Wood has values or powers that cannot be quantified in scientific terms. These aspects of wood, without being well-understood or even explainable, may well be among the most important and powerful. However difficult they are to describe or define, we can at least demonstrate their certain existence. (Location 3037)
  • When this balance of moisture exchange is established, the amount of bound water eventually contained in a piece of wood is called the equilibrium moisture content (EMC) of the wood. The relationship between the amount of bound water in wood and the RH is shown in Figure 6.3. In my estimation, this is the most important item in this book. (Location 3171)
  • Figure 6.3 • This may be the most important information in this book. Hang a copy of this graph on your shop wall and look at it every day. The amount of bound water in wood is determined by the relative humidity (RH) of the surrounding atmosphere; the amount of bound water changes as the RH changes. The moisture content of the wood when a balance is established at a given RH is its equilibrium moisture content (EMC). The solid line on the graph represents the relationship between EMC and RH for white spruce, a typical species with a fiber saturation point (FSP) of about 30% EMC. It is a fair approximation of the relationship for most common woods. (Location 3179)
  • cold. It is important to realize that if the absolute humidity of air is unchanged, lowering the temperature of the air raises the RH, while heating the air lowers the RH. (Location 3213)
  • thinking of an equilibrium relative humidity (ERH) rather than an EMC to emphasize the fact that RH determines EMC, not the other way around. It is prudent to think that “my lumber should be at equilibrium with 40% relative humidity” rather than that “my lumber should be at 7.5% moisture content.” (Location 3233)
  • Figure 6.9 • Freshly cut 10-in.-wide red oak planks on a workbench top would shrink as the wood dried, leaving cracks. where ΔD = change in dimension due to shrinkage (Location 3741)
  • It somehow seems absurd that although men have walked on the moon and heart transplants succeed, we still have wobbly chairs. (Location 4008)
  • When contemplating problems such as internal/external joints where restrained swelling is likely, remember that the elastic limit of wood under compression perpendicular to the grain is on average less than 1%, so that restrained swelling of the magnitude of 1% may be setting up a problem. (Location 4037)
  • If bowls are green-turned to wall thicknesses of ½ in. to ⅝ in., a wood with average density such as black walnut can be treated with a moderate schedule (e.g., three weeks at 70°F in a 30% PEG solution or one week at 140°F in a 50% solution) to achieve a high degree of stabilization. (Location 4317)