ETC 1250 Lesson 06a - Lesson 6a Introduction ETC1250 -...

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Unformatted text preview: Lesson 6a Introduction ETC1250 - Properties of Materials Wood has universal appeal- - It is generally pleasant in appearance 0 Chapter # 6 - Most wood has a pleasant odor . _ - Because of its poor heat-conducting properties, it feels P98 264 272 warm to the touch Wood is an excellent material for Doors Door and Window frames Flooring Trim Items where appearance is of primary importance Wood is used extensively in dwellings where feelings of comfort and well-being are especially desired Growth of Trees _ Growth of Trees Trees are Either Wood consists of long, narrow, hollow cells called fibers - Deciduous - - ° Bark _ r . . . — The outside layer — Egmozrjiad leaves and usuallyf shedding them in the falt ' _ _ Protects gmwing cells from insects e Useless as a stmctural material — Tight, complex grain - Cambium layer earlywood — Thethin, rowing layer at the outsi e of the tree 'atewow - Coniferous .- ' I — New fibers grow each — Having needles and cones containing seeds 9 A Season, IncreaSln the _ gomods -' - - diameterlayerby ayer — Elroad, simple grain growth ring vascular cam biurn - Hardwoods are generally harderthan soltwoods, but there are exceptions, — Douglas fir and southern pine are harder than some hardwoods — Basswood and poplar are softer than many softwoods “1,15,. secondary prunern Dark com came (3 2006 Merriam-Webster; he, Growth of Trees Growth of Trees Wood consists of long, narrow, hollow cells called fibers Wood consists oflong, narrow, hollow cells called fibers - Sapwood - Pith — W'rthin the cambium layer, — A thin vein of 5011 tissue at the center — Fibers are active in the life processes of the tree — Extends the length of the tree — Do not grow — Has no strength - Heartwood earlywood - Rays — Nearlhe center of the - — Growtransversely, tree _ 'aTEWOOO forming radial lines from 'aTeWOOO — Con5ists of dead fibers gmmhring vascular the center. ' ' hri" vascular . — Useful in thelife 9'0"" 9 . - Heartwood and sapwood . -- Gamb'Um rocesses ofthe tree _ _ .. camoiurn do not differ in mechanical . _ ' . _ . .- — 0 not affect strength properties ' 3 — Influence the appearance _ of finished lumber Heartwood is a darker shade because ofthe resins, gums, and minerals It contains early wood Il'll'lBl'{ secondary WW“ I tnner{ secondary Drum Dark cork camorum Dark com (:3me © 2006 Merriam-Webster; he. (9 2006 Merriam-Webster; inc. Growth of Trees The fibers of all wood species consist of Cellulose — A structurally sound material 7 Approximately 70 percent of the volume 7 Paper is made of the cellulose from wood — Wood destroying insects survive on cellulose and water Lignin — Is the cement — Approximately 25 percent Miscellaneous substances Growth of Trees Springwood and summerwood form: alternating concentric bands around thetree Summennvood: because of the thicker fiber walls, is: — Heavier - Dancer — Harder - Stronger early wood The strength of wood can bejudged by: — The percentage of summerwood compared to springwood 'aleWWd - A higher percentage of stahmenivood results in greater growth ring strength and greater weight — The unit weight or specific gravity Growth of Trees A pack of drinking straws held together with rubber bands approximates the fibrous structure of wood. Hollow fibers — Easily crushed or pulled apart in a transverse direction — Have a great deal more strength longitudinally Bundles offibers — Lateral forces can collapse the long, nanow fibers without crushing any fiber walls. — In the longitudinal direction, the resisting walls are too long and close together. If stress is applied in any direction between longitudinal and transverse. the resisting strength varies from maximum in the longitudinal direction to minimum in the transverse direction. Growth of Trees Spring and early summer — springwood or early wood — The forming of newfibers — growth proceeds rapidly — Large, thin-walled fibers Summer and autumn — summerwood or late wood — Growth is slower — Greater perc entage of fiber wall material earlywciod ! t ed Cold weather a em — There is no growth growthring Old growth forests produce woods with tightly compacted grain because the lack of direct sunlight promotes slow growth Modern timber farms produce woods with looselyr compacted grains because rapid growth is promoted Growth of Trees Wood floats because it consists of hollow fibers containing air — Specific gravity less than H} Wood with the fibers saturated (waterlogged) is heavier than water — Specific gravity greaterthari 1.0 20 The hollow cells of a tree contain water both within the hollow space and within the cell walls The total weight of water olteri exc eeds the weight of solid material. Morsture evaporates from the wood alter the tree is dead until an equilibrium Is reached with the air's relative humidity. The free water in the hollow space evaporates first with no change in the volume or the wood. When the free water is gone, absorbed water evaporates from the celt walls, causing shrinkage of the wood. - This shrinkage is the cause of cracks inthe wood called checks Growth of Trees When wood is sawed parallel to the length ofthe tree: the light and dark annual rings appear as stripes called grain. The grain (and therefore the fibers) may be inclined to the axis of the piece of wood because ofa branch nearby or because of a bend in the tree. — This deviation in direction of grain is called slope otgrain — Slope in grain away from the axis weakens the wood for normal usage The growth of new cells on thetrunk partially encloses branches that have started to grow and forms a discontinuity in the ring pattern — The discontinuity appears as a knot in a piece of lumber — The branch mayr die and the branch stub become completely enclosed within the tmnlc forming a loose knot — The branch mayr continue to grow and form a solid Knot Whether loose or tight: the knot causes weakness — Loose Knot center has no more strength than a hole — Solid knot center is somewhat weak, because its cells are approximater perpendicular to the long axis of the wood Lumber Production In the forest Two basic methods of saWing a log into Trees are felled Cut and trimmed into logs Hauled to a sawmitl for sawing into lumber Kept moist while stored at the mill to prevent shrinkage cracks. unless they will be stored only a short time. Lumber Production m lumber y I. Slash—cut lumber I — Plain sawed in the terminology of the ‘ hardwood industry — Flat grain in somvood terminology “1‘ — Typically used for dimensional lumber. such as 2x4's \‘ Rift—c ut lumber — Quarter sawed when referring to hardwoods — Edge grain when referring to so‘l’cwoods — Typically used for decorative hardwoods, such as flooring Also a combination method Lumber Production Seasoning is the process of reducing the moisture until a suitable moisture level is reached Lumber to be finished may be planed — While green S-GRN = Planed before seasoning — Or it may be seasoned first and planed later S—DRY = Planed aher seasoning The cross section of the wood becomes smaller during seasoning. — If lumber is planed lo the proper size alter seasoning, it will remain the proper size. — If it is planed first, it must be left larger than the proper size to allow for shrinkage to the proper size. Lumber is sawed to nominal sizes {usually to the whole inch) — But the width of the saw blade reduces the size somewhat Planing reduces the size further to the correct net or finished size at which the lumber is sold Lumber Production At the mill - Blades remove bark beforethe log is sawed. - The sawyer decides how.r to saw the log for maximum production on the basis of its — Size — Shape — lrregularities - The log is then — Sawed lengthwise into large rectangular and semiround shapes for further sawing into lumber sizes. — May be cut directly into lumber thickness by gang saws cutting the log into man},r slices at once - Saws called edgers — Tn'm the roughedged slabs longitudinally to the desired lumber width — Cut off the rounded edges - Saws called trimmers — Saw the lumber transversely into desired lengths — Tn'm away defective portions. Lumber Production Lumber is finished in one of several ways. - Rough lumber remains as sawed on all four sides with no funher finishing. Dressed lumber or surfaced lumber is planed or surfaced on at least one face. It is designated as — 818 if surfaced on one side, — 81E if surfaced on one edge, and — SlStE if surfaced on one side and one edge. — The abbreviations s25, s2e, sls2e, s251e. and s4s are used for other combinations of sides and edges that are surfaced Worked lumber is dressed and atso worked to provide — Tongue-and-grooveiomts — ShiplaijlnIS — Andror to change the cross section in some other way Lumber Production / Thickness Lem—l"h One board 1001 Lumber is measured and sold bythe foot board measure (fbm) — One board foot is a quantity 1 sq It by 1 "1 thick Board feet. = [total iength in feet] x {thickness in inches] 3 {width in inches)! 12 Finished lumber is calculated using nominal dimensions so width and thickness are always in full inches Finished lumber less than an inch thick is considered 1 in thick Lumber length is rounded down to the nearest foot Lumber Production Th ckness 12‘ mg m One board ‘but Examples - Calculate the number of board feet in (36) 2x4’s which are 8’-3"' long Board feet = (36 x 8ft) x2in x 4in l12(inift) = 192 bf Calculate the number of board feet in {24) 3/2" x 6" planks which are 10’-1D" long Board feet = (24 x 10ft) x 1 in x Bin I 12(inlft) = 120 bf Assignment - Page 317 Review Questions 1 & 3 If you do not understand a question, email me at tomlinm@9hcc.edu or through myPHCCedu ...
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ETC 1250 Lesson 06a - Lesson 6a Introduction ETC1250 -...

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