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hammer
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A tool consisting of a metal head set perpendicular on a handle, used for driving nails.
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hardboard
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A pressed homogenous fibreboard having a mean density of not less than 800 kg/sq m.
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hardness
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A property of wood that enables it to resist indentation. It is measure in kN and is often determined by the Janka hardness test.
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hardwood
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A general term for timber of broad leafed trees classified botanically as Angiosperm. The term has no reference to the relative hardness of the wood.
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heartwood
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The wood making up the centre part of the tree, beneath the sapwood. Cells of heartwood no longer participate in the life processes of the tree. Heartwood may contain phenolic compounds, gums, resins, and other materials that usually make it darker and more decay resistant than sapwood.
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hewn timber
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Timber with or without wane, finished to size with hand tools such as an axe or adze.
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hit and miss
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Areas on dressed or moulded boards that that are not fully machined. It results form unacceptable unevenness in the
thickness or width of the boards. It is also called skip.
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hobnail
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A pattern of pin-holes left by insect attack.
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honeycombing
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A drying defect which occurs when tensile stresses in the core (usually a result of collapse) result in the formation of internal cavities.
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horizontally laminated timber
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Laminated timber designed to resist bending loads applied perpendicular to the wide face of the laminations. For vertical loads, this means that the wide face runs horizontally.
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housed joint
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A joint where one piece is notched or grooved to receive the other piece.
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humidistat
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A device for automatically regulating the relative humidity of air.
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humidity
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A general term for the presence of water vapour in air. There is a known limit to the amount of water vapour that air can
hold at any particular temperature.
Absolute - The amount of moisture in air. It is usually expressed as the weight of water vapour in a unit weight of dry air
Relative - At a given temperature, this is the amount of moisture in air as a percentage of the maximum moisture carrying capacity of the air.
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hygrometer
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An instrument for measuring the humidity of air.
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hygroscopic
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Changes its moisture content to be in equilibrium with the atmosphere.
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hygrostat
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A device for automatically regulating the equilibrium moisture content of the air. See also Humidistat.
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hyperbolic paraboloid shell
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A complex curved surface which has one line which is always straight.
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hysteresis
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As applied to timber's moisture content, the tendency of dried wood to reach equilibrium with any specified temperature and relative humidity at a lower moisture content when absorbing moisture from a drier state than when losing moisture from a wetter state.
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