SURINICAGF OF WOO D
May 194 7
No. R1650
UNITED STATES DEPARTMENT OF AGRICULTUR E
FOREST SERVIC E
LFORES`l -PRODUCTS LABORATOR Y
Madison, Wisconsi n
In Cooperation with the University of Wisconsin
SHRINKAGE OF WOO D
By
EDWARD C . PECK, Technologist
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Moisture in Wood .
The large quantity of water that most green wood contains may be separate d
roughly into two parts, that which is contained as free water in the cel l
cavities and intercellular spaces of the wood, and that which is held as
adsorbed water in the capillaries of the walls of such wood elements a s
fibers and ray dells . It is the adsorbed water, amounting to about 30 per cent moisture content based upon the oven-dry weight of _the wood, that is
of primary interest in the consideration of shrinkage, because when-thi s
-water is removed the finer wood, elements approach each other and thereb y
cause shrinkage .
,
Effect of StructureOf: VoQd-U
-Sr
Wood is composed of hollow fibers or cells, most of which--lie nearly parallel to the axis of the tree trunk . The cells of the ,wood rays, however ,
are perpendicular to the main body of cells . The cell walls that sur r°und
the open spaces, or cell cavities, possess a crystalline structure (fig . 1) ..
In normal wood, the greater part of the crystallites of the ,cell walls ,
both in the main body` of cells and in the wood-ray cells, are. oriente d
nearly parallel to the axis of the tree trunk . The crystallites of th e
primary cell wall, which lies in-the center of a wall between two cells ,
are oriented, however, so that they fall in planes perpendicular t_o, th e
crystallites of the rest of the cell walls . Since thecrystallites ar e
joined end to end, when the water between them is removed they approach
each other in the lateral directions only . The crystalline structure, o f
the cell walls, and the opposing structure of the different crystalline
parts of the cell walls, somewhat like crossbanded plywood, make the shrink age of wood, complicated .
When water, is removed from between the crystallltea ._of the cell _wall, they
approach each other and thereby cause the wall to decrease in thicknes s
and in circumference . The cell cavities tend to remain the same size durin g
the shrinking of the cell walls, because of the nature of the cell-wal l
structure . The volume of the cell walls decreases by an amount equal t o
the volume of the adsorbed water removed from them . Since the shrinkag e
along the length of the crystallites is zero, and since the majority of th e
crystallites are nearly parallel to theaxis of the tree trunk,",the volu metric shrinkage of the cell walls is translated into decreases in the
Rept . No . R1650
lateral dimensions of the wood, radial and tangential . Since the crysta l
lites of the cell walls Of the wo•od~-r-ay-cells are nearly parallel to the
'
axis of the tree trunk, but nearly perpendicular to the axis of the wood-- ,
ray cells themselves, the wood-ray'cells shrink chiefly along their length ._
If they did not act in this manner, they would seriously restrain radia l
shrinkage .
Directional Shrinkag e
Wood shrinks most in the direction,o .f .the annual growth rings (tangen- tially),_'about one-half as much as this acros s, these rings (radially), .and
very . little, as a-rule, along the grain (longitudinally) . The causes o f
these differences in shrinkage are the he x:arOgeneous'nature o f . wood-and
the complexities of the .cell-wall structures In some abnormal types o f
wood, such as compression wood In conifers and,awood of exceptionall y - low specific gravity in hardwoods, the longitudina)•shrihkage is unusually great .
This is accounted for by-the fact that the -crystallites of the cell wall s
of such types of 'wood 'make a considerable angle to the' axis of the tre e
trunk, instead of being nearly-parallel to it, ,In general, the springwood• of the annual ring tends to shrink more "longi t dinally than the summerwood ;
and less laterally, for the same reason.
Moisture Content-shrinkace Relationshi p
Wood starts to .shrink'when it begins to lose the absorbed water . The removal of the frea water, which is held in the cell cavities, does not caus e "
shrinking; ' :The-cell walls, as previously statdd, when -complete•ly- full o f
water contairi-'about 30 percent moisture . "content based upon the .oven-drys .
weight of the wood . This condition is called the fiber-saturation `point .
The shrinkage that occurs when the moisture content is reduce d . balow -th e
fiber-saturation point Is basically dependent" pon the amount of moisture
removed-from the cell walls . In 'drying wood to a 'moisture content of 15
percent,- one-+ho.lf of the total shrinkage takes place ; while in drying i t
to a moisture'content-'of-6 percent, four-fifths of the total shrinkage
takes place . For practical purposes, swellin g' nay be considered the-re.verse of shrinking . Although basically the moisture content-shrinkage, .
curve Is . a straight line 'fro m . the fiber-saturation ._point t-o ' zero moil- ~
tare content it actually is not so, because a piece of wood doe s 'not dry
simultaneously from all parts . For purposes of calculating shrinkage, o r
swelling, the moisture content-shrinkage relationship may be considered a
direct one . The mbtsture cdhtent-=Shrinkage curve in figure 2 i"s typfcal .
Shrinkage Variability
One of the prominent things about shrinkage is its variability. Shrinkage
not only differs along the three directions of grain, tangential, radial ,
and longitudinal, but among species . It varies widely in material cu t
Rept . No, 81650
'
from the same species and even in material cut from a single tree, Woo d
of high,specific gravity generally shrinks more than wood of low ape-cia o
gravity, which would be expected because wood of high specific gravit y
contains a greater volume of water at the same percentage of moistur e
content than wood of low specific gravity . 'Another thing that contribute s
to-the variability ofshrinkage is the change in volume of the cell cavi ties, either "a decrease, which may be called collapse, or an actual increase .
In the first instance, the shrinkage is greater than the amount calculate d
on the basis of the volume of the adsorbed moisture with the assumptio n
that the cell-cavity volume remains unchanged ; and in the second instance ,
it is less than the shrinkage calculated on that basis . The changes in
the volume of the cell cavities are caused by drying stresse s i or in some
instances by liquid tension . Because drying stresses influence the change
in volume of the cell cavities, an d , consequently-the over-all shrinkage ,
the amount of shrinkage is affected by the drying conditions . Generally ,
the higher the temperature and relative humidity, the greater is th e
shrinkage . Water-soluble . extractives -influence shrinkage and tend to re duce the amount .
The shrinkage variability within e. single species is illustrated i n
figure 3 . The values, total shrinkage in width of plain--sawed longleaf
pine heartwood boards, range from 3 .9 to 9 .0 percent, with a mean of 6 . 9
percent .
The volumetric shrinkage curves in figure 4 illustrate the shrinkage vari ability within pieces cut from the time log . The specimens from which th e
data were obtained were cut from a single radial board . The straight
lines are the shrinkage curves calculated on the bases of the specifi c
gravity of the wood and a fiber-saturation point of 30 percent . Since the
hygroscopic water is compressed, its specific gravity is 1 .11 instead o f
1 .00 . Consequently, the volume is reduced so that 30 grams of water occup y
only 27 cubic centimeters, The actual shrinkages are represented by th e
curves., It is notable that considerable shrinkage occurs before the aver age moisture content has reached 30 percent, because the outer parts of th e
pieces have reached a moisture content below 30 percent . The calculate d
shrinkage is not attained in some instances, while in others it is exceeded .
Despite the variability of shrinkage, the Forest Products Laboratory ha s
accumulated, over a long period of time, shrinkage values that may be considered approximate mean values for the various specie-s ., Table 1 give s
these shrinkage values in percentages based upon the green dimension .
Although the shrinkage values of the table are given in percentages of th e
green dimension, they can be converted by simple manipulation to useful
units of measurement . Each 3 percent of shrinkage is roughly equivalen t
to 1/32 inch per inch of dimension .
An examination of the total shrinkage values in the table discloses tha t
the following ranges exist : volumetric, redwood 6 .8 to hickory 17 .9 per cent ; tangential, redwood 4 .4 to hickory 11 .4 percent ; and radial, northern
white cedar 2 .1 to hickory 7 .3 percent . Hardwoods shrink more than soft woods, on the average, by 13 .5 to 10 .3 percent for total volumetric shrinkage . The hardwood possessing the lowest shrinkage is mahogany, which i s
Rept . R1650
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not a native wood. Of the . native hardwoods,; butter4ut.: os.qesses thy ; lgwest. . .
shrinkage, - Of - the softwoods, tamarack pdsse-s er. the. _highest shrinkage, and i s
followed by western larch . The ratteo of total, radial4to tQ al_ .,tangeritial
shrinkage-ranges-,fr p m 1- :1,2 in evergreen magnolia to 1 :26 in Eastern whit e
pine, . Although in general the woods of high specific gravitypossess-ttie highe r
shrinkage, there _ are exceptions . Basswood-,' a-light wood, has a high shrink age, while black locust, a heavy wood, has a moderate shrinkage,
.
The amount of shrinkage, and the ratio of the directional shrinkage affect
the development , ; of seasoning , defects during, drying. In ether instances ,
they help deterAi.ne the use to which the seasoned lumber . is .put .
%
-
If wood did not • shrink; during . drying, most of the difficulties related t o
seasoning would not exist . Shrinkage is , responsible for decrease in dimension, loss of footage, distortion in cross section, warping, surface an d
end checking, 'h©neycombing and drying'andcase-hardening stresses . • - :,Shrink-age enters-the,'pieture as soon as . the :-tree is cut into logs . The drying
from the,: freshiy„ cut ends is likely, to-cause end checks beca11a the dry •en d
, surface is attempting to shrink . If the logs remain in the woods or in_:a dry yard for a considerable period before sawing, especially in hot, dr y
weathers -..the- ;end& ohecks may -exten d' for a considerable length into -.the_-iog . ' • . .
After, the lumber - i& sawed,._ and= before it is piled. for air,seasoning or kiln
drying, exposure.: .to44evere'drying conditions, particularly direct sunshine, . _
will cause end and surface :checking,
. : -During:. seasoning, when any part of ;thei_piece reaches a moisture conten t
belawr .the fiber-saturation-point, 30' .percent, .it assumes a, tensile-.stress .
Under-the influence of this stress, it' shrinks, fails, -becomes . "set ;• o r
remains :stressed . Failure of surface layers"under shrinkageestrsss-result s
in end checks ; which -may . develop into splits'•or--end: honeycomb,°checks.; and
in surface checks, which may-develop into splits ; orhoineyeomb checks .- Failure-of internal parts results in the formation_ef .honeycomb checks,
If the
dried part does not fail, it assumes a set, which is one of the steps i n
the development of a final-case-hardened oondition ; When the piece .of woo d
has become thoroughly seasoned, the 'results of shrinkage are evident .- The
.
piece will be thinner, narrower, and shorter than it was when--green
The shrinkage in thickness is of importance in making the proper allowanc e
in setting the head saw or gang saw for the green thickness . If the boards .
are sawe,ci too thick, a wastage of- weed results, even though all boards .
dress to,the =desired dry thicknsav .' _ -If the boards are sawed too thin, '
too large•a percentage of them will fail to .make the required dry thick
ness .- Owing to the variability in shrinkage, it is impossible to saw th e
boards 'tis a green'-thickness so that they all will make the desired dry a .
dressed thickness without excessive waste :; 'The optimum green 'thicknes s
should produce a certain relatively_ large--percentage of boards that dress :
to the required dry thickness . - The percentage 'of boards that should dress Rept, No,. P1650
- -4-
A'
to the desired dry t h 'j ckne a ' s shoo]:& be determined on An -e o oa~.i ' baste,
. , v;
The sawing allowance-for=shrinkage is influenced - by species,- tom= of. lumber, 1
and-by warping . Some species 'shrink more than others ; fore exarsple',one- :mil-l
cutting southern yellow pine, . cottonwood, yellow-poplar, and black tupelo
• on a gang: saw was experiencing difficulty . with respect totscanty; thicknes s
with the cottonwood and black tupelo, but not with the other spehibsa
Plain-sawed boards shrink lessthickness than quarter-sawed boards, bu t
the outer edges of plain-sawed- boards are often equivalent to quarter-sawe d
boards. Warping causes difficulties in attempting to dress to a certain
thickness . Shrinkage in width is important, because . it usually causes a
reduction in board footage, particularly ducting kiln drying ; The loss i n
foetage is affected by the species, type of ]umber, and width of the board s
and will be greater in those species having a large tangential shrinkage ,
in wide boards, and in plain-sawed lumber . Board footage losses, in kil n
drying air-seasoned lumber from an average moisture content of 18 percen t
down to 5 percent, have been calculated . The figures are based on kiln
charges of plain-sawed lumber of normal width .distribution . Wider than
average boards will- exceed the footage-loss figure . Quartersawed board s
will ordinarily not suffer any appreciable loss in footage, since the total
radial shrinkage is less than . 6 .3 .percent for most species . Figure 5 shows
the estimated reduction in footage in percent
of . air-dried tally, based on
..
the total tangential shrinkage value ..
Although the wood fibers or coils shrink but slightly in length, a bbard r
is seldom cut so that its faces and' edges are parallel to the fibers . Thenature of the dross section•, •therefore, will be changed when the board dries .
A square cross section .will no longer be .square, but may be .rectangular o r
diamond-shaped. A circular cross section will no longer be-circular (fig .. 6) .
Warping, which can'be broken down into cupping, bowing, crooking, and .twist'- '
ing ti . may take pace . Zipping may be brought about by the . nonsimultaneousdrying of the two facers, or- by the greater , shrinkage of the outer face of ' a
plain-sawed board.. The other three forms of warping usually result fro m
combinatioi'of-shrinkage with such irregularities of grain as spiral ,
diagonal, or localized irregularities, or with abnormal wood having a
greater than normal longitudinal .shrinkage, such as compression wood or very
light wood from buttressed tree bases . . Although warping is caused by shrinkage, it is well to bear in mind that much warping is also the_result of poo r
-lumber piling.
Shrinkage causes the greatest damage when it occurs after the lumber has
been put into a'structure or the wood has been fabricated into finishe d
articles . Changes in dimension, usually shrinkage but sometimes swelling ,
-cause defects . Shrinkage in structural members causes settling of buildings and loosening of fae.tenings . Settling of buildings causes plaste r
cracks,- distortion of, openings, uneven floors, and unsightly openings around .
trim . and moldings .. ` Shrinkage. of studs, sheathing, and siding decreases the
weather tightness of the wall, loosens fastenings, and reduces. the mechani
cal strength and stiffness of the wall . Shrinkage of subfloors and floors .
causes :squeaky floors and unsightly floor cracks . Shrinkage of trim and
paneling causes open joints, exposure of unpainted streaks, and possibly
warping and splitting, Shrinking stairway parts cause squeaky stairs and
Rept . No . B1650
Shrinkage ,of ,doci:rg causes. . un s ight .uni5ainted . streaks' And joints
Shrinkage in boxing :and . crat i .ng . lumber .causes loosening of :-fasten- .
poor fit
open
infix and . .splitttng , , .w-ith consequent weakening of the. package . Shrinkage o f
. parts after their Manufacture into furnitu.re,. .cabinets, and . case goods ,
reislU.t in waxping, -splitting, cracking, failure 'Qf joints. , and dimuni,-:tion of the strength ." .
- . .r .1
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. ■
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.
1:
_ I
I
, :-, . .
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-
Rept . No . R1650
..
Shrinkage
Species
t
='
Air-dried to 15 perc9ent
moisture contend
(estimated values)
: Radial
:
3 .6
2.3
3-9
4 .0
2 .0
1 .8
1 .9
2 .6
'
Z M 87996 F
2 .2
1 .4
:
33 .4
.2 =
1 .8
1 .7 s
2 .0
1 .8
2 .5
I Percent - :Percent :
7
6.4
6 .6
5 .8
5 .2
4.1
.7
6 .2
4.3
3 .0
3 .6
s
4 .6
4 .3
1 .8
2 .1
4 .8
4.4
2 .4
s
3 .3
4 .4
1 .5
2 .2
2
j .4 .
.0
4 .4
2 .1
3 .3
4
t
!
s
t:
t;
1 .6
2 .1
2 .2
2 .6
2 .7
1 .8
2 .6
3 .4
4.4
33
2 .$
3 .5
4.6
3 .4
33 .8
.1
1 .14
)
•
Oven-dried to 0 percen t
moisture content
(teat values)
!
Tangential
Tangential•Volumetric Radial •Tangential Volumetric Radia l
:Percent : Percent
Alder, red
Alaska yellow-cedar
Ash :
Black
Commercial white
Oregon
Aspen
Baldoypress
Basswood
Beech, American
Birch L
Birch, paper
Butternut
Cherry, black
Chestnut
Cottonwood :
Eastern
Northern black
Douglas-fir
Coast region
Inland Empire region
Rocky Mountain region
Elm
American
Rock
Slippery
Fir
Balsam
Commercial whiteHackberry
Hemlock :
Eastern
Western
Hickory :
Pecs ;
True_
Honey locust
Incense-cedar
California
Larch, . Western
Locust, black
Magnolia:
Cucumbertree
Evergreen
Mahogany
▪
Eiln-dried to 6 percent
moisture content?
(estimated values)
•
:
8 .2
.1
5.8
5 .8
7 .e
6 .2
5 .9
5 .33
3 .00
5 .5
5 .0
:
3 .0
a 2 .7 :
, 3 .1
. 2 .9 .
1
4 .0 s
3 .3
s
.
3.8 :
.
.
.
4 .8
.
6 .0
6 .8
9 .0
5 .4
8
6.6
4 .9
6 .8
6 .2
3 .8
2 .8 .
4 .1
7
.0
6 .9
4.4
4.9
6 .9
.
:
:
3 .9
2 .2
2 .6
3 .8
2 .4
3 .4
3 .9
5 .8
3 .4
2 .6
3 .4
3 .5
: Percent
10 .1
4.8
: 3 .7 •
: 3 .3
:
Percent
.
:
.
.
.
:
.
.
1 4 .2
. 4 .3 :
. 2 .8 s
6 .o
6 .5
5.
5 .0
b .8
7 .1
4 .9
5. 7
5.
7 .4
6 .9
6 .2
5.0
7 .6
7 .1
5 .3
5 .7
7 .1
5 .4
6 .3
7 .1
9 .1
5 .3
4 .2
6 .5
5 .5
7 .11
:Percent :
Percent
4 .4
2 .8
5 .0
4 .6
4 .1
3 .5
3 .8
.6
556 .1
6 .9
6 .3
3 .3
7.3
6.0
7.8
7 .5
8.1
6.7
6.2
9 .3
11 . 0
8.9
8.6
6.1
:
12 .2
.
10 .2
10 .6
9 .2
12 .6
13 .0
13 .0
18 .2
9 .3
11 .3
9 .9
9 . 14
8 .7
8 .5
11 .7
11 .3
11 .0
8 .6
7 .8
. 11 .0
7 .8
9 .5
: 10 .9
114 .3
8 .6
. 6 .1
10 .6
. 7 .8
10 .9
9 .8
6 .2
3 .4
3 .9
3 .6
.0
4 .1
3 .6
4 .2
. 4 .8
. 4 .9
. 2 .8
2
4. 8
3 .0
4 .3
4 .9
:
3
4 .2
: 33 .3
44 .2
: 4 .4
5 .2
5 .4
3 .5
:
.
.
:
:
.
•
.
.
.
.
:
:
:
.
.
:
:
.
:
Percen t
•
•
12 . 6
9.2
15 . 2
12 . 8
▪
13 . 2
11 . 5
•
15 . 8
16 . 3
10 . 5
16 . 3
16 . 2
10 . 2
11 5
1. 1
9 .2
8.6
7 .8
7 .6
.2
6
9 .5
8 .1
8.9
6.6
7 .1
6 .9
6.8
7 .9
8 .9
11 4
6 .6
5 .2
8.1
6.9
8 .8
6.6
4 .8
Volumetri c
11 . 6
-s
14 . 1
:
11 . 8
10 . 9
10 . 6
12 . 4
14 . 6
14 . 1
13 . 8
10 . 8
9 8
1 .8
3
9 .7
11 . 9
.
13 . 6
17 . 9
10 . 8
7.6
9 .8
13 . 6
.3
7.7
13 . 2
s
Table 1 .--Shrinkage values of wood based upon its dimension when green
species
Maple :
Bigleaf
Black
Red
Silver
Sugar
Oak :
Rea?
white$
Pine :
Eastern white
Loblolly
Lodgepol e
Longleaf
Ponderosa
Red
Bhertleat
Sugar
Western white
Redoedar, Eastern
Redoedar, Western
Redwood
Spruce :
Eastern%
Engletoann
silks
Sweetgum
Sycamore, America n
Tamarack
Tupelo :
Black
Water
Walnut, black
Wnite cedar :
Atlantic
Northern
Port Orford
Yellow-poplar
(Continued )
shrinkag e
Eiln-dried to 6 percent
Oven-dried to 0 percent
Air-dried to 15 percent
moistur e content
moisture contentll_
moisture content5.
(test values )
(estimated values)
(estimated values)
Volumetric
: Radial : Tangential :Volumetrio :Radial :Tangential : Volumetric : Radial : Tangential
:
;
° ----°
1
t^ Peroen t
lpercent : Peroent : Percent :Peroent : Percent
Percent :Percent : Peroent
11 . 6
: 3•7
1 .8
3 .6
5• 7
9 .3
7 .1
5 .8
3 .0
14 . 0
11 .2
4 .8
9 .3
2 .4
4.6
7 .0
3 .8
7.4
13 . 1
2 .0
4 .1
6 .6
2
6 .6
10 .5
: 4 .0
8 .2
12 . 0
6 .0
2 .4
5 .E
7 .2
1.
36
9 .6
: 30
14 . 9
11
.9
4
.9
9
.5
2 .4
4 .8
3
.9
7
.6
t
7 .4
:
:
:
9 .0
:
14 . 8
2 .2
4 .5
7 .4
4 s 7.z
11 .E
4 .3
16 . 0
12 .8
5 .4
9 .3
: 2 .7
4 .6
8 .0
: 4 .3 s 7 . 4
2 .3
6 .0
8. 2
: 1 .2
3 .0
:
4 .1
: 1 .8
4 .8
6 .6
12 . 3
: 2 .4 s 3 .7
6 .22
t 3 . 6E
5 .4
:
9 .g
:
7 .4
1
11 .3
2. 2
4
S5
: 33
4
9
.5
6
12 .
4 .1
9 .8
5
7 .5
: 2 . 6 : 3 .8
6 .1
5 6 .0
54 .1
.1
:
3 g
b .3
i
9. 6
: 2 .0
.0
: 4 .6
1 : 5 .0
33 .2
7 7
t '4 . 6
2
s
11 . 5
2 .3
3 .6
s
.E
t
8
9 .2
21 .4
.2 : 3 .8
: b .2
i 3 . i b .2
9 .E
29
. 67
12 .;
3
2 .8
i 4 .0
: 2 . t 4 .5
55
7 .4
:
11 . 5
: 2 .0 1 3 .7
3 . s 5 .9
9 .4
: 4.1
5 .9
:
7.8
3 .9
: 2 . t j .8
s
6 .2
t 3 .1
4 .7
: 1 .6
2 .4
t
11
.0
6
.2
2
2
.4
5-(
4
1
8
1 .2
2 .5
3 .8
: 1 .9
2 .6
1- 7
1 .3
2 .2
3 .4
: 2 .1 t
3 .5
5 .4
12 . 6
6 .3
. 3 .4 : 6 .2
10 .1
4.
2 .2 1 3 .8
10 . 4
g $
6 :6
1 .7
5 .2
2 .4
55
11 . 5
: 3 .8
5 .8
: 2 4
6 .0
:
9 .2
t+•3
7 .5
7 .5
4 :2
7 .9
: 12 .0
: 5 .2
9 .9
5
2 .6 : 5 .0
t
1 24 . 2
1
3
:
4.1
5
.3
11
.4
5
.1
7
.6
2 .6
.8
7 .1
13 . 6
: 3 .0
:
1
1 .8
6 .8
5 .9
: 10 .9
: 3.7
7 .4
3 .7
s
:
7 .7
3 .8
1
7 .0
3.
6 .2
11 .1
2
4. 11 1
13 . 9
2 .2
12 . 5
6 .1
10 .0
4 .2
7 .6
2 .1
3 .86 .2
} .4Z
11 . 3
2 .6
3 .6
5 .7
1' .2
5 .7
9 .0
5 .2
7 .1
s
:
5 .2
4 .2
6 .77
2 .E
E.4
1 .4
2 .6
: 4 .2
1
2 .2
2 .1
4 .7
7.0
1
1.0
2 .4
: 3 .5
1 .7
3 .8
5 .6
10
.1
2 .3
t
5
.0
8
.1
4.6
6
.9
3 .4
3 .7
5 .5
12 .3
: 3 .2
5 .7
9 .8
1
4.0
7 .1
2 .0
3 .6
6 .2
1
-
?These shrinkage values have been taken as one-half the shrinkage to the oven-dry condition as given in the last
three columns of this table .
2
-These
shrinkage values have been taken as four-fifths of the shrinkage toltse oven-dry condition as given in
the last three columns of this table .
Average of sweet birch and yellow birch .
'Average of grand fir and white fir .
akverage of bltternut hickory, nutmeg hickory, water hickory, and pecan .
Average of ehellbark hickory, mookernut hickory, pignut hickory, and shagbark hickory .
7-Average of black oak, laurel oak, pin oak, northern red oak, scarlet oak, southern red oak, swamp red oak, water oa k
and willow oak .
-Average of bur oak, chestnut oak, post oak, swamp chestnut oak, swamp white oak, and white oak .
2Average of black spruce, red spruce, and white spruce .
Z M 67997 F
1
v
N
e,
(NOSNJ/v/c. N3~~ liv~~~~d)
~~r
: ..
25 -
20-
5-
Ol
/
2
3
4
5
6
7
8
SHRINKAGE IN WIDTH - TANGENTIAL (PERCENT OF GREEN DIMENSION )
Z H 67995 F
Figure 3,--Frequency distribution of total tangential shrinkag e
values of plain sawed boards of longleaf pine heartwood .
9
r
r
z m
42062 F
• rgure 4 .--Volttet;ti•c shrinkage curves of four pieces of sycamore
cut from t' he.e4 radial board . Straight lines represent the
calcnIate•d :0 1iikiges, based-on 30 percent of water by weight ,
but 2Z..per,ent by volume ; curved-lines, the actual shrinkages .
6
I
J
9
/0
6
7
8
TOTAL TANGENT/AL SHRINKAGE (PERCENT)
Z Y 36992 F
figure 5 .--Estimated reduction in
tally) vs . tangential shrinkage
.
green) for carload shipments of
a moisture content of 5 percent
of 18 percent .
footage (percent of air-drie d
(percent of dimension whe n
hardwoods when kiln dried - t o
from an air-dried conditio n
//