September W. 1917 



5 '1*1 



The Shrinkage of Wood 



FIG. 1 



FI6.3 



■50f17o shrinkage- 



TIlltEE IHKECTION.S OF SllKINK A(iE 

 Viz. 1. t;iii,i;eiiri:il shl'iiika;;e, niiiy he N per eeiit ; Fig. 2. raiiijil. ."j pel- cent; Fi;.'. 



tpue-Iifth rif 1 jier cent 



The vv o r k e r in 

 wood has the jirob- 

 ■ lem of shrinkage be- 

 fore him always. It 

 may be a serioins 

 and perplex! n y 

 problem, or it may 

 not amount to much. 

 It depends upon the 

 kind of wood and 

 hon- it is being- lian- 

 dled. 



When green wood 

 is subjected to dry 

 heat it parts with 

 moisture and con- 

 tracts ,in volume, 

 but no precise ratio 

 exists between the 

 quantity of water 

 expelled and the ex- 

 tent of the shrink- 

 age. Actual tests 

 are required to show 



the contraction in bulk of a certain kind of wood during the drying 

 process; and in order that one wood may be compared to another, 

 it is necessary that all be subjected to the same treatment. That 

 usually consists in reducing the specimen from a green to an oven- 

 dry state. Oven-dry wood is drier than it is ever made in a kiln. 



Wood shrinks more rapidly toward the end of the seasoning proc- 

 ess than near the beginning. It does not shrink equally in all direc- 

 tions; but most tangentially, next radially, and least lengthwise. 

 Tangential shrinkage lessens the circumference of, a round log; 

 radial shrinkage lessens its diameter; and lengthwise shrinkage 

 shortens it. Shrinkage in all three ilirections lessens the log's 

 volume. 



It is not possible to name a precise rate or amount of shrinkage 

 for wood. Each kind has a rate or amount of its own; and the 

 behavior of one is no guide to the behavior of others, because one 

 may contract two or three times as much as another. As nearly as 

 averages can make a rule, it may be worded thus: Wood shrinks 

 lengthwise one-iifth of one per cent; radiall.v live per cent; and 

 tangentially eight per cent. A round log 42 feet long and 20 inches 

 in diameter when green, would, if the above rule is applied, have 

 the following dimensions when oven-dry: Length, 41 feet, 11 

 inches; diameter, 19 inches; circumference, 56 inches (a reduction 

 of about four inches in circumference). 



It should be clearly borne in mind that these figures are intendei! 

 to apply in a general way only, are based on averages, and may not 

 hold true if applied to a particular wood. In many individual cases 

 they certainly do not hold true. 



Shki.n'k.vge IX Volume. 



The theoretical instance above given of the shrinkage of a log 

 while in the process of seasoning from the green to the oven-dry 

 state, makes it clear what is meant by volume shrinkage. For 

 comparison 's sake, figures are given below of the volume shrinkage 

 cjf a number of woods. Each log, block, or parcel of wood is under- 

 stood to contain exactl.v 1,000 board feet in its green state, and 

 the problem is, to ascertain how many feet will be lost in changing 

 it to an oven-dry condition. 



The data from which these \alues have bejn calculated were 

 recently published (in the form of percentages) by the Forest 

 Products Laboratory, iladison. Wis., in Bulletin No. 552. This 

 bulletin, which was comjiiled by H. S. Betts, from the work of 

 \arious persons, is one of the most valuable, from the lumberman's 

 staiid]ioint, ever issued by the Forest Service. It deals with the 



FIG.2 



— SFMAXWELi^ 





seasoning of wood. 

 Figures on the vol- 

 ume shrinkage of 

 w o o d s in passing 

 from a green to an 

 oven-dry state fol- 

 low: 



Fci'i hi 

 Wwiil 1.000 lost liil 

 Mhrinkagi- 



HlCIvOHV 



Sha^bjirk hickor.v lG«i 



risment hickor.v. 172 



ilookornut h'kor.v 177 



Shellbark hickor.v li)2 

 .Vsii 



nine ash 117 



I'nnipkin ash. . . . 120 



<Treen ash 12,'» 



12« 

 131 



l.-)2 



len^'lhwise. nnl.\' 



l*ust oak loi; 



Can.von live oak 1 112 



Spanish oak Hi;: 



Water oak 104 



Chestnut oak I(i7 



Swamp white oak 177 



Willow oak LSI) 



Laurel oak 104 



<'o\\- Liak 11*4 



.M.U'l.K 



llroatUeaf niajile ll*i 



Soft or sllvei- maple 120 



Red maple 12.T 



Sugar nniple 14.'i 



l';i..M 



*'<irk or i-tick elm 141 



White ilui 144 



Slipper.v elm 14."i 



JIlSCELI,.\NKOfS IHunWOOPS 



ItiK'kthorn caseara 7t> 



Honey locust .S(i 



Osage orangre Sli 



Yellow liicust OS 



Butternut 102 



Sassafras Hm 



Black walnut 11;^ 



.\speu lis 



Biltnioro ash. 



White ash 



Black ash. . . . 



O.IK 



r.urr oak 127 



Calif, black oak.. 1:^1 



Yellow oak 142 



Red oak 143 



White oak l.'i" 



Yellow blleke.ve 120 



1 'herr.v 121 



.Magnolia 123 



Tupelo (cotton gun) 124 



Keil alder 12(i 



Silver bell 126 



Cott(mwoo(l 130 



Fraser umbrella 130 



< 'huiquapin 132 



Willow ". . . ISo 



Cnciunber 136 



Black gum 139 



Ilackherry 139 



Sycamore 141 



Moimtain ivy 144 



Chestnut 146 



Sweet birch 150 



Sourwood 152 



Bas.swoo(I 155 



Beech 161 



Holly 162 



Paper birch 163 



Yellow birch 16K 



Mailrona 169 



Dogwood 1S5 



Serviceberry 1,S7 



Witch hazel 1,S8 



Eucalyptus 225 



list may be noted. The 

 taken 



es are 



Yellow poplar 114 



The omission of red gum from the abov 

 government bulletin from wliich these vain 

 data for that wood. 



The list below giN es the shrinkage of \arious soft woods. 



Ffft ill 

 1.000 loKt bii 

 Uinifl -shriiikaffr 



I* INKS 



A\'hite ijiue ■. . . . 78 



Sugar pine ,S4 



•leffrey pine Oil 



Western yellow pine 00 



Jack pine 104 



Table mountain ifine. . . .- loo 



Pond pine ll'J 



LfKlgepole pine 114 



Norwa.v pine 11.'. 



Western white pine ll.'i 



Pitch pine 117 



I.oiigleat' pine 122 



I.obolly pine 126 



Slash pine 127 



Fiu 



Alpine tir oo 



White fir lO'J 



|Uotes 



no 



Fi'rt in 

 1 .000 lost bil 

 Wood shriiikaffr 



P>aisam hr IDS 



Orand tir 109 



Douglas hr 121 



.\oble tir 136 



Lovely fir 141 



Other Softwoops 

 .Nni-tbern white cedar (arbor- 

 vita') 70 



Western red cedar SI 



Yew 97 



lOugelmann spruce 104 



Hemlock 104 



Sitka si)rnce 112 



Bald cypress 115 



Red si>rnee 118 



Western larch 132 



White spruce 148 



Tamarack 136 



—21— 



