3 '861000
U. S. Department of Agriculture, Forest Servic e
FOREST PRODUCTS LABORATOR Y
In cooperation with the University of Wisconsi n
3
MADISON, WISCONSIN
q 73
VENEER & PLYWOO D
Reprinted fro m
AIRCRAFT DESIGN DATA BUREAU OF
CONSTRUCTION AND REPAIR NAVY DEPARTMENT .
1919
'44V-N
UTTEER IND PLYWOOD *
Venee r
Veneer may be loosely defined as thin wood . It usually varie s
in thickness from one-hundredth inch to one-eighth inch, though it i s
commercially possible to cut it thinner, and thicker sizes are to b e
obtained . However, in general, veneer used in aircraft falls withi n
the limits stated ;
There are three common methods of manufacturing veneer, a s
follows : (1) The rotary process, (2) the slicing process, (3) the sawin g
process .
By far the greater portion of all veneer manufactured is mad e
by the rotary process . Veneer made by this process is all slash cut ,
and the length along the grain is limited by the length of the venee r
lathe . Rotary veneer longer than 100 inches is more or less uncommon .
Sliced veneer is usually manufactured only from the finer woods .
On account of the fact that it is possible to rroduce quartered venee r
on slicing machines, and the waste on account of saw kerf is absent ,
this method of manufacture is preferred where pattern is important an d
the value of the wood is great . The length parallel to the grain o f
sliced veneer is limited by the length of the knife .
;awed veneer can be uroduce', in almost am reasonable length
and from any kind of stock . The material p roduced may he Other quartered or slash . In general, sawed veneer will not be soeci .f'iet for aircraft uses, to the excli'o ion of rota= stock, exceut where it i s
necessary to have extra . long lengths or quartered . stock or for som e
other reason it is impossible to secure the stock by rota= chtting .
It may happen, for instance, that the stock from which the veneer is t o
be cut can not he handle r, to advantage in a rotary lathe on account o f
its shape .
A special series of test ; was made to determine the effec t
of the method of cutting veneer on the strergth of plyr ood panels mad e
from it . Detailed results are resented in tahle 7, and . the enera l
conclusions dramn follow :
(a) The effect of the method . of cutting veneer on the strengt h
of plywood depends on the suedes cut, although in general, the effect ,
* Reprinted from Wood in Aircraft Construction, Note No . 12, 'aircraf t
Design Data, U. S . Navy De p artment, prepared by Forest Product s
Laboratory .
R973
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(b) Of the three methods o' cutting, the sawed and . sliced
material, for the species teetee,, .:ave the more similar results . The
commercial white ash, sngar n .3:D1e, and yellow ponlar panels cnlt b y
these methods were sligstly superior in bending and tensile strength
4' the rotary-c-at panels .
(c) For birch the panels of rotary-cut veneer were sli g;htly
superior in bending and tensile streath to panels of either sawed or
sliced veneer .
(d) For the species tested, with the possible exce p tion o
iier4kcsn mahogany, panels of sawed veneer twist less than panel s
of either sliced or rotary-cut veneer .
(e) With the ercention of birch the resi,lts show little
difference in the twis t ins of panels of sliced or retains-cut veneer .
For the convenient ca2culation of the woiaht of veneer an d
plywood, table 8 has been prepared . This table presents the wei7hts ,
per square foot,- of vesleer of'yarious file-messes and species, at th e
average air-dry moisture condition shown in the second column . The
weight of-blood elhrmer gIne per square foot and the weight of a
typical oasein Flue (0ertns) per square foot are also given, so
eitot.
it is possible to calculate the average weis-ht of an : nlys's .oi ,mbide
up _of .
liste l and
blood or casein glue . This i s
done
J sing to-:ether the weights of the individual nlieo an d
the w
0I ]We tine, hich is obtained by mn1tiplYins' the weis'ht o f
mare foot by the nu:Men of glue lines in the plywood .
lUs4pairl4ba, ..,ess than the number of plies .
While it is usually not necessary to know the ts-oliae strength
of single-ply veneer as such, this fi gure is verr convenient in comput the ?robable stren s th in torsion of nlywood made up in various
Banners . The last column of table 9 presents com2utsd tennile strength s
of sinsle-plY veneer . Pefc-enee to the other c3ata in this table wil l
be found in the text vnder the discussion of nly wood .
Plywood
'1 41
In general plywood consists of a number of layers If TIV6 &
veneer gilled to-ether by some suitable glue or adhesive . Oce'7msAII.Esally
the term is applied to material in which one or more of the kwers ar e
composed of some other material than wood .
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about 50,000 tests hale been made and tabulated . Since the s nbject i s
rather new, a full Ois e rssien is pres e atea, follo w ed by tables o f
strength properties .
Propertiee of Wood Paa1lcl and Perendicriar to the Grai n
Wood, as is well known, is a nenhomogenous material wit h
widely different properties in the various directions relative to grain .
This difference must be recognieed in all wood construction, and . th e
size anrf form of parts and placement of wood should . be srch as t o
-dtilize to the hest advantage the difference in properties along and
across the grain . It is the strength of the fibers in the direction o f
the grain that gives wood its relatively high modulus of rryture, an d
tensile and compressive strength . parallel to the grain . Were it a
homogenous material, such as met iron, having the same strength propertiee in all directions that it has parallel to the grain, it woul d
be uneycelled for all strrctrral parts whore strength with small weigh t
is aeeirea . As it is the tensile strength of wood . may bo 20 time s
as high. parallel to the grain as perpendicular to the grain and it s
modulus of elasticity :Cram 15 to 20 times as high .
In the case of shear the strength is reversed, the shearin g
strength perpendicular te the grain being much greater than the strengt h
parallel to the grain . The low parallel-to-the- g rain shearing strengt h
makes the utilization of the tensile strength of wood along the grai n
difficult since failure will rsrally occur through shear at the fasten-.
ing before the maximrm tensile strength of the member is reached .
The large shrinkage of wood across the Train with changin g
moisture co tent may introduce distortion in a boar d that decrease s
its uses where a bread flat eurface is desired . The shrinkage from th e
green to the oven-dry condition across the grain for a flat sawn boar d
as determined. by the average of 150 snecies is abort P per cent, and fo r
a quarter-sawed board. about 4 1/2 per cent, while the shrinkage paralle l
to the grain is practically negligible for most snecics .
Plywool Panels v . Solid Panel s
It is not always poseible in a given use so to proportion a
board or solid panel as to develop the necessary strength in ever y
direction and at the same time to utilize the full strength of the woo d
in all directions of the grein . In such cases it is the purpose o f
plywood to meet this deficiency b?r crossbanding, which results in a
redistribution of the material .
In building tip n1 word a step is made in . obtaining equalit y
of properties in two directions -- parallel and perpendicular to th e
R9'73
-7-
A
i
edge of a board . The greater the number of plies used . for a given pal
mss, the more nearly g
homo eneous in properties is the finishe d
Thus, in an airplane engine mounting made of 15-? ;lr veneer the
ehanical properties of the panel in the direction narallel to th e
4r-ain of the facets are almost the same as those in the dir e,ction at righ t
angles to this . However, an increase in such properties as bondin g
strength and modulus of elasticity at right angles to the grain of the
n
faces is accempaniod by a decrease of the values p arallel to the s_,
of the faces with an increase of the number of plies ; or a very Inv:
number of plies (of the same species and thickness) we may assume tha t
the tensile strength in the two directions is the same, and that M .
equal to the average of the parallel-to--the-grain and pee endi+etOi ere-to the-grain values of an ordinarTr solid board or panel . This is net always
exactly true, since the maximum stress of the plies with the grain a t
right angles to the force may not be reached at the same time as the,
maximum of the plies with the grain parallel to the force .. In.ttAa1 l
stresses due to change of moisture content may also tend to unbalanc ' the strength ratio .
tel.
Symmetrical Construction in Plywoo d
On account of the great difference in shrinkage of wood i n
the direction p arallel to the grain and perpendicular to it, a chang T
in moisture content of plywood will inevitably either introduce o r
release internal stresses . Consider, for ewample, a three-ply c n
struction and subject it to law-humidity conditions, so that trt maitp w
ture content of the plywood is lowered . Because the grain of the tOo'P.
is at right angles to the grain of the faces, the core well tend shrink a great deal more than the faces in the direction of the gtra'% o f
the fates . . This shrinkage subjects the faces to compression strosset
and the core to tensile stresses . If the facer are of exa6tl r the same
thickness and of like denazify ; the stresses are s emnotricaiIy distribute d
and no cupping should wsiOlom4'
Now consider that one face of a three-ply pa-nil has been glue d
'with the grain in the same direction as the core and that the r
t?3x e
content of the panel is reduced . It is obvious that the internal stresse s
are now no longer symmetrically distributed, inasmuch as the compressiv e
stress in one face has been removed . This face now shrinks a g roat deal
more than the other face in the direction of the grain of the latter .
The result is that cupping takes place . Figure 29a shaows the effect o f
drying on a three-ply construction (unsymmetrical) in which the grai n
of two adjacent plies was parallel . The panel has curled up into a
cylindrical surface with the parallel plies on the inner side . . By
adding another ply at right alle les to the core we see that symmetry mltt
again be established and that while we would have a four-ply panel i n
reality it gives a three-ply construction with a core of deuhle the faO,
thickness and would be regarded as such .
The necessity for exercisina care in sanding the faces of a
panel is obvious, inasmuch as different thicknesses on the faces would .
introduce uneqnal forces with changing moisture content .
I . order to obtain symmetry, it is also necessary that both
faces or symretrical plies be of the same species .
To summarize : A veneer panel must be eymmetrically ceastracte d
in order to retain its form with changes ; of moistnre . Symmetry is obtained by reing an odd anrber of plies . Tae plice should be so arranged
that for any ply of a particular thickness there, is a parallel nly o f
the same thickness and of the eame species on the opnoeito side of the ,
core and equally romoyed from the co : e .
Direction of the Grain )f djoiniq
Plie s
In
discnlslon of sYmrstry of coastnretion it was nnderstood that the adjoinine; plies were always seined with the g rain eithe r
parallel to or exactIv at right angles to the core . In careless construction this may rot al w aYs be the case . An eatrene case of this kind
is shorn in fignre 291, in which the nlies were _ - ire' so that the eraloo
of each face of the oenel was at -5 degrees w ith tho grain of the cor e
and so that the two faces w ere at 90 decrees with respect to each ohor .
Thereae the unsymmetrical conetruction intro ices cupnint, a constructio n
involyins: aneles other than 0 And 90 degrees intred .nace twisting .
La bnildin nj a three-ply veneer panel the care ehorl d
glued with the grain at 90 degree with the facce or as close to thi s
as feasible .
Effect of Yoisture Conten t
The nrevioue discusaion ban broualt out the fact that a chang e
in moisture content of a panel may iatroduce cupping and twistiag in th e
panel if the panel is rot caref-elly oonetrnrted . 7ence it is highl y
desirable that the moistrre content of the veneer before glning b e
controlled so as to make the meisture content of the finished panel when
it leaves the clamps about the same as it w ill averag e neen in use an d
that all plies Is at the sarco moisture content bofone elniala .
The limit s
of from 1C to 15 nor cent moisture in tae finished panel will usuall y
give satisfactory reenlta when the panel is in service in the open air .
Shrinkass of Plywoo d
The shrinkaee of planood
vary 7 j th the species, the .rati o
of p17 thickness, the number of plies, and the coabination of species .
R973
-5-
The average shrinkage obtained in 54 tests en a variety of combination s
of species and thicknesses in bringing three-n?y mood from the soaked t o
the oven-c'r7 condition was 0 .45 p er cent parallel to the face grain an d
0 .07 per cent rerneadi.cnlar to the face grain, with the ra_ eee of fro m
0 .2 to 1 per cent and 0 .3 to 1 .2 per cent, roceectively . Other combinations and thickreeses may ext . r.d these limits and chan ^e the averag e
somewhat . The species incl .uied in the tests made were rahecany, birch ,
poplar, basswood, red `_nn, chestnut, cotton giro, elm, and pine .
Effectof Va7lu ` tie Tnnber o
Plie s
The gnestion frequently arises, Should +h ree or more plies b e
used. for a panel of a given thickness, The rarticnlar use to which th e
panel is to be nut m p ot answer this gnestion . Commercial considerations
will also enter . Veneer of most species less than 1/ 1'8 inch thick ca n
not be cut by the rotary p rocess with uniform success, and while a
number of s p ecies may be cut by slicing to 1/64 inch and less, such
material is limited in width .
In general it -ay be said that the greater the number of -one s
the flatter the plnvood -i11 remain ;hen suh~-ected to moisture variations .
If the saint.e bez c.i .i; or tensile stren , is desired 1 n the tw o
directions, parallel and perpon r'_ici-lar to the grain of the faces, th e
greater the nrmber of plies the more nearly the desired r . eshit is obtained . Thin same reeolt may be obtained by a proper selection of ratio
of core to total plywood thickness in three- p ly construction . It mus t
be borne in mind, however, that a ply rood with a lar. . e, number of plies ,
while stronger at right an •los to the grain of the faces, can not be a s
strong parallel to the grain of the faces as three- p ly noo'_, and henc e
a three-ply panel is n_ refcrahle whore greater strength is desired i n
one direction than in the other . Table 11 gives strc . :gth values fo r
three-ply, five-pl :r, and seven-ply yellow birch plywood .
There great resistance to splitting is desired, ouch as i n
plywood that is fastened along the edges with scre w s a .n1. belts and i s
subject to forces tore h the fastenings, a large number of ;lies affords
a better fastening .
It is a common e xp er i e nce that a :tined joint is meakeaed whe n
two heavy laminations are g l u e d with the grain cresscel . T^_e. same weakness exists in nlyood . when thick plies are g lued together . When ply*rood is s bject to moist'ire c antes, stresses in the clued joint du e
to shrinkage are greater for the thick nlie then for the t h in plies .
Fence in p lywood con_stru'.ct.e wi th many thin ,lies the g lue d L joints wil l
not be as likely to fail as in nlyrr ood constrrctea of a smaller numbe r
of thick p lies .
R973
-6-
Effect of Varyingthe Ratio of Core to To t,1_'I'h
fa-les s
At first thoi :ght it may seen that the nronor selection of th e
ratio of core to total Dl rood thickness in three-nly corstr-etion ma y
enable the desitne^ to got the same strength in both directions as i s
possible with many-plied navels. While this is tree in r eneral, i t
is not trre that the same ratio will serve for both tension and bending .
In birch, for exam p le, a ratio of core to total nlSweod thickness o f
5 to 10 gives the same strength in tension in both directions, but a
ratio of abort 7 to 10 g ives the same strength in bea d ing . P)r eithe r
ratio the nl7wood is not nearly as resistant to splitting as nlywood o f
a greater ni_'rrber of tiles totaling the same thickness .
Species of Igor,Density for Core s
There column sere_ _°t' :_ and a flat panel are desired, ful l
advantage of a strong species, such as birch, in the faces is bes t
attained by using a thick tore of a s p ecies, such as basswood o r
yellow poplar, rather than a thinner core of the g ame weight but o f
a sneoies of greater density . A combination_ of stroll , faces and a
thick light rood core has the advanta g e of greater separation of th e
faces than when using the thinner core of a heavier species, givin g
a marked increase in the interial resistance to forces that tend t o
bend the panel and a correspondingly great strength in bendin : with th e
same weight .
Consider, for example, that a certain panel contains a cor e
of the same weight but of a s p ecific gravity of one-half that of anothe r
core . This means that the core of linhter species is trice as thick a s
the core of high density and that the panel faces are spaced twice a s
far apart . In a long column, for instance, this is very desirable, fo r
the maximum load a column can carry varies as the cute of the thickness .
It is evident that a narked superiority in the load sustained might b e
exn ected in the low-density core Hanel over the hi.9h-d.ev..sity core pane l
of the save we ight when the load is applied parallel to the grain of th e
faces .
The same line of reasoning aneli e ry. to co l , 'mn strer.oth. may als o
be ap p lied to resistance to cunning . A Panel with a core of low densit y
will cup less than a uanel of the same we i ght wi th, a core of high density .
The load to nrodrce failure in bending would 1E-revise be g reater for th e
former case .
Plywood TestDat a
The co l rmn-bending o-odulus is obtained by loa, .in a piec e
of plywood 5 inches by 12 inches as a column with the 12-inch length
R973
-7-
vertical . It is comn1-tei b7 the followin g formula :
S .~ P + 6th , whe r e
A bd
= Column-bendin g nioaulus .
1 = Area of cross section .
P = Load. at 'oaaimun moment .
M = \r axi.mum bending moment .
= -'idth of test -niece .
d. _ Thickness of test piece .
test, the
fibers at
magnitude
withstand
Like the modulus of rupture in the standard . static bending
column-bending modulus is not a true stress existing in th e
the instant of failure . It is merely a measure of th e
of the external bendin gmoment that a piec e of p lywood ca n
before it fails .
If a piece of nly'oo ? i>> subjected to forces that tend t o
bend it, as would be the case either in a long column_ or in a beam ,
the designer confronted . with the problem of determining its grope r
thickness may use the column-bending mod-elm in exactly the same wa y
that the modulus of rupture is used . It will be noted, of course ,
that the column-bending modulus must be used which aD i:lies to th e
particular plywood construction desired . The total plywood thicknes s
is to be used in all equations involving the column-benai_n g modulus .
The use of the tensile strength data. is obvious . The
strength values given are based or the total ulyrood t' .ic'_kness .
(Table 9)
6amule
Co g-prtatio n
To obtain the tensile strength of 3-ily wood conoisting of tw o
1/20-inch birch faces and. a 116-inch basswood core .
Parallel to face grain = 2 x 1/20 x 19,060 = 1,98E founds pe r
inch of width .
Pe rp endicular to face g rain = 1 x 116 x 9,450 = 591 - p ound s
per inch of width .
This co :nnutation n e g lects ti :e tensile strenct of tie ply o r
plies per-pendic--lar to the 7ra .i.n, which is co :uaratively small . The
results are therefore slightly in error .
R973
-8-
TABLE 1` T0 . 9 . -- Tensile_ Strength of Fliliod and Venee r
:1inrber
:r,/oisttre :Specific
:of tests :at test :gravity*
:(percent) of ply.
wood .
Species .
_
(a)
12 0
200
200
1'.0
20 0
11 5
11 5
40
1='0
(b)
9 .1 :
(c)
0.49
: Tensile
:stren7,th**
:of 3-nly
:rood para].lol to
:grain of
faces
: (n .>,'n'_ s
:per sq uare
inch) .
(d)
: Tensil e
:strength** *
:of single :-:ly veneer ,
: 1 1/2 (d)
:(pounds pe r
: s qnare inch )
.
.
6,180 :
6,510
6,880
(e )
9,27 0
9,7'7 0
10,32 0
A sh, clack
:
Ash, commercial white,
10,2
.60
.
9 .2 :
.42 :
Basswood
::
L3,000
19,50 0
.
8 .6 :
.67 :
Beech
; .
19,80 0
13,900 •
Birch, yellow
8 .5
.67
.41
5,200 :
7,80 0
Cedar, Spanish
13 .3 :
3,450 •
12,69 0
Cherryl
9 .1
.56
f , 30
6 1 64 5
.
11 .7
.13
Chestnut
.
10,92 0
.
7,2 :0
Cottonwood
8 .8
.46
.47
6,360
9,84 0
Cypress, bald
35 .
10 .3
9, 34 0
Doug las fir
17 4
3 .7 •
.49 •
;, 230
12, 66 0
Elm, cork
65 .
9 .4
8, 40
Elm, wlite
.52 :
5,860
8,79 0
160
3 .9 :
Gtun, black
3,960 :
10,44 5
35 .
10 .5
.54
9,39 0
Gum, cotton
80 .
10 .3 :
.50 :
5,260
7,350
Gum, red
3
.7
.54
:
11,77
5
182 .
:
Hackberry
80 .
.2
.
.54
•
6,920
10,38
0
10
0
Hemlock, western
9
9
.7
:
.^7
:
6,300
:
10,20
11
4.0 ,
Wagnolia2
9 .9 :
.59 :
10,000 :
15,00 0
1..'ahogany, African 3
20 :
12,7
2
:x,370
3,06 0
Mahogany, Philip p ine 4
25
10 .7 .
.53 .
10,670 •
16,01 0
Maho g any, true
.48 :
6,390
9,58 5
35
11 .4 :
12,270
Maple, soft 5
120
8 .9
.57
8,180
15,290
Maple, sugar
202
8 .0 :
.68 :
10,190
Oak, commercial red
115
9
:
.59
5,480
8 , 220
:
.3
Oak, commercial white
195 .
9,5
.64 :
6,730 :
10,09 5
.43
Pine, whit e white
40 .
5,640
8,460
10 .2 :
Poplar, yellow
165 .
9 .4
.50 :
7,390
11,080
Redwood
65 .
.41 :
5,100 :
7,650
11 .2 :
Spruce, Sitka
.
.A3
5,600
8 .400
103
8 .4
Sycamore
9,2
3,030
12,04
5
163 .
9
.1
:
12
.375
Walnut, black
.
110 .
.59
3,250
*Specific gravity based on oven-dry weight and volnme at test .
**Based on total cross-sectional area .
***cased on assumption that center ply carries no load .
Data based on tests of 3-ply panels wit' ._ all plies in any one panel same thickness and species .
'Probably black cherrT . 2Probably evergreen magnolia . 3Prsbably k:naya sp .
4Probably tangrile . SProbably silver maple .
R973
-9-
s8
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The resistance to solittin : is of considerable i^:port°a .nce i n
nanels when these are to be fastened with eere w s or holts and . are ells ec t
to forces at -Cae fasterinTs . 71e nrmerical value of fte work relnired to
has no direct application in desi7n .
split n, nanel of a ed.ven t : 'c7
It is only in comparison with ether panels of other stecies or constrrction that work in erlitting was any si g nificance . The work done is, o f
course, a measure of resistance to selitting . It is not entirelY a property of the woo d , as it donende verY lan g ely u'oon the streegth of th e
glue .
The results of strength toots on nl7wood of varions commo n
veneer species are given in table 10 . Excont for 1iirc :-:: all tests are
on onln one shipment of thp opecies, so that the roe alts rill in al l
probability be changed lomeWlat by the additien of fat''''e test data . Th e
mahogany res"lts are on thin plywood. rangin in thicnees from 3/30 inch
to 3/16 inch, while the sizes of the plywood for all other m :)ocies range d
from 3/30 inch to 7/6 inch .
In most
caece it was found that the eolnmnebonding modnlue o f
thin nlywool was 3lightl7 lose t'-.an the colnmn-bening modnlns of th e
thick plywood .
TABLE 11 .-- C r -rearjjL?n ofStre , l e te of..2, 5 and 7 Pl . X211or . 3i
'Ill - Plies_ of Same _T11i el : :sees in try„n e; Panel .
:Column-bend:ing molnlus ,
: Tension, i n
: nonnds -,)e r
squar e
inch
"
:Para,:Per. :penli,5 :llel- :-)en d ie
Numbe r
:AyeraTe :Avera g e : Ppmber : in nonnds
of nlies :s-pecific :per cent :
of :e 'er squar e
:gravityl.;moisture :tests : inch .
:Pa n a- :Per-
:11 123
5
7
0 .57
.57
.70
:
:
:
8 .5
6,3
7 .1
:
:
oo d
:Lveral:e slitting
resistance compared to 3-pl y
birch, for th e
'same olywoo d
:
f-ieeneos i n
nor (-p it o f
7-ol n .
195 : 16,000 : 3, 2 00 : 13,200 : 7,700 :
25 : 14,700 : 6,800 : 13,100 : 2, 6 00 :
25 : 14,300 : 7,900 : 1 2 ,900 : 9,'00 :
100
12 9
19 1
1
Specific gravity,
1-teed on oven-dry w eight and volume at test .
Parallel ani -oereendicular refer to direction of grain
relative to direction of aunlication of fo r ce .
face s
Table 11 shows the decrease in the nmit strength of plywood in th e
direction of the grain of the faces when the nnmber of nli-ee is increased, an d
the increase in the nnit strengtt of plywood pereendicnIar to the Train of th e
faces when the n'obe- of riles is increased .
-10 -
1
-
shows that., L Tae strength values
tr ;nvo)d p arallel t o
arc p racti .call - r the ,,arse f )r three-ply wood lavin g
a core of dense wood as for lJiv rood
a core of light wood . Th e
strength %wax.es across the Train of I.L@ dQc.ee are, however, very muc h
less for the p lywood with core or Lew N,kV t-r` .
In other wor=Is, the strength
values of three-elv wool narallel to the grain of the faces are almos t
°ely determined by the s.t e_ .lth values of the face material, and . th e
1al-les across the c rVin of the fa€os IloP l eery lar g o
.deter!rino d
1'en' th value g• of the core si ecice .
wig
the t -
Tabla 1$ ices a n1 nr, , .bPr of factors r,at are o ft', vaire in selecting
w
srecke of daft Dlies for a three-plv = p anel .
The thickness _f4ctor (K s.) is tzs•ed to obte .id the thickness o f
a -niv of any Species having ti some tctal ben ing stren,oth as a liven pl y
of birch . It is arri wed - at's follows :
`lae strength of any struct-ura-l member i ; •doh rni~ned ert
*wet load it can sD thin or the brendi ag moment it can resis without l
rettre . t niYrrood the latter factor is the g etter criterion of ' stre h f7th . ti
If we denote the maxim= bending moment of a stria) of three-ply wo'oA 1 inch ,
wide and of thickness d l by M1 and the stress at failure by Sl (coll ribending modulus), then Ml . = S1. a1"
I .
`
6
fI
ihi
'Sirs^ .il,arl -, the strength. of ar:o cr s ; irj of a
sspecie s
will be denoted 14 . M2, its stress at fa-12uro S 2 , and thickness ' •;' ,icy a
.P17-per selection of thicimos d2 the s.eee.nd strio rra ;r b e9 made t,;0 9 withstan d
the same ma-As-rum bending moment, so tat Y _ Ml or S2d2' = S ra~ ' .
Frown thi a the ,desired thickness d2 =
Taking d z. as t ho wait o f
ir.~m the maxirnrm stresses in .k11,-1
t
general, ? a =~ 7 0, where
1
M
oo .
V ^a
F^~ S
zs the thickness of the my oad., w1-_oso Q~ll'rnr .a riding modulus correszd .s to S and whose total bending stren
i l■JI
, Ti a by the tending moment ,
t
1.9 the same as that of birch ol-Tooot
- i•
! 6.,. . ■
'rho same reasoning also ap-olies to single nli o s, so
ds may
bt wolf +,o 9'et the thickness of a single nl r, which will give
sam e
tAml bending streng'th as a birch ,ly of thickness unit,, .
*lcamnle ,
for yellow porlar T s = 1 .46, and a nl of this species, 1 .1-6 -x 1/1 6
0 .091 inch, is egnivalent in strength in bending to a birch sly 1/16 inc h
thick .
thickness of a birca plywood: stri p
nercentas'e of birrih,, we have 1,4 =
8973
I
cL
08,,
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TABLE 13 . -- Tuickress Pcc :ors f(T.. ?cpee r
Giving : (I) Veneer tl :icl-ress for the same total ber , 'ing strength as birch ;
(2) veneer tl-icloness for the same weight an birch .
Species
blach
A.sh,commercial wlllte
Kr
D.
S.
r's
Avera7e ;
specific :Speci''ic :Pe r cent :Pe r cent : facto r
:gravity of :=2,-ravity :moisture : unit : for the :f)ctor fo r
specie s l :of glued : of -o l ,,k- :be:ding : same to- :t0s e sam e
ba.sed on :plywood :wood as
: tested .
oven-dry : as
:-ei-r:ht and : tested : :
air-dr
:
v ;1rane .
ash,
Basswood
B eech
Birch, Yellow
Cedar, Spanish
Cherryb
:
:
:
Elm, cork
Elm, white
:
:
Fir, Douglas
Gin, black
Gum, cotton
Gum, red
7T-ac'k -hJerrv
Hemlock, western
Wagnolia
Vahogany . ,ifrican
Vahou.,any,Phil ipoine' lWaho k,any. , true
Waple,soft°
Wanle, sugar
Oak,cowercial red
39
43
44
66
51
c 51
52
:
:
52
49
5A
1'2
:
:
: 0 .40
:
.60
:
63
a 34
51
44
Chestnut
Cottonwood
Cypress, bald"
0 50
58
51
a 46
1 57
'71 49
48
02
:
:
:
•
.12
:
37
:
9 .1
10 .2
9 .2
8 .6
:stren:: t h :tal bend- :welght a c
:comrarcd :
ing
:
: with :stren7th :
0 .63 .
: b I rch . 2 :as bi r ch, :
D
52
:
94
.37
.41
:
8 .5
: 13 .3
.46
.47
:
:
8 .8
10 .77
.62
.2
:
9 .1
8 .9
.50
.5 4
.5/
.47
: 10 .3
:
8 .7
: 10 .:
9 .7
:
9 .9
:
.72
.53
.48
: 12 .7
: 10 .7
: 11 .4
8 .9
:
:
.56
.43
.49
.54
.52
.57
.8
.59
.34
:
9 .1
: 11 . 7
48
:
:
100
43
:
80
34
:
56
53
•
:
1 .39
1 .12
:
:
1 .2 6
1 .09
:
1 .03
:
1 .00
1 .12
1 .72
:
:
1 .24
1 .43
:
:
:
•
73
58
:
:
8 .0
9 .3
9 .5
:
:
:
:
:
:
1 .4 7
1 .4 3
.9 5
1 .31
:
1 .24
:
:
:
:
1 .2 1
1 .29
1,1 7
1 .50
:
1 .2 4
:
1 .3 7
1 .34
1 .37
1 .13
:
1 .55
1 .29
36
:
1 .3/'
S9
57
74
100
59
59
:
:
:
:
:
:
1
1
1
1
1
1
:
1 .6 6
1 .00
1 .8 5
48
54
55
60
67
:
:
:
1 .00
1 . :2
1 .29
1 .34
1 . 44
1 .25
: 8 .7 60
56
:
10 .6
:
:
1 .44
1 .2 2
.21
.32
.16
.00
.30
.20
:
:
:
:
:
:
:
:
1 .24
1 .2 1
1 .1 0
1 .29
1 .3 1
1 .0 2
1 .0 0
.9 1
:
:
63
Oak, commercial white :
69
:
:
52 :
1 .38 :
1 .61
Pine,white
39
:
.42 : 10 .2 :
9 ./- :
58
:
1 .51
:
1 .E- 4
P9r, lar, yellor
50
:
1 .7 5
:
49
:
1 .43
:
Redwood
a 33
:
.41
: 11 .2
71
:
1 .09 :
1 .2 6
Sycamore
50
:
.5E :
9 .2
:
:
S p ruce, Sitka
:
50 :
1 . ,1 :
1 .66
:
.43
:
8 .4
55
0
'7q lnut,
J.I
83
... . . . . . .
_ 1 .10
;'laken from Bulletin 556 of the U. S . Deuartment of A,ric u lture
.Average of the column-bending mo-l rlli narallel and neruendicular to grain compare d
to 'birch .
°Probably silver maple .
ased ort -libsequ-rIt tests . A 4 0oat tlrce Doug las fir .
uProoac'y 'tangrile .
e mbably black cherry :
R973
:.
II
1
. .-
I_ I
; _An
1,
:-
1(
undeuetoe ,i 4 hat unit bendin g
27 ray of es-71seekess $t must
Issstnre, o r
strength refers to a maximum treso suah as the roduluo
th e
the coligressbending meOuTus,
total beTe7ing strenth refess
load or bending moment baw Ma?' sustain or the bonding moment 4 *olsml
can sustain .
It should b@ kept
d that t7ese facters w s-Jl11 AISOokless b b
swewhat b7 furthe r
@1
4
The thicks *lit** 1(70
d to obtain the thic hmes s
y ef 7ellow birch of given
ply of any species equal in wel;ht to
of oirch by the
vidi
he 0
ness . It is obtained by simolT e dens
density of the species tau
'1'ed .
_lit
State s
data used in computing Y7 arc,*
at e ive.
moods
Department of. A e rie-allure 2,4:eirt 556,
ap ical •
frown in the
lne
State ." The wei eht
n,es,lecteds
1
I I
For 7-.@i.low parlor, fo-r eXample, t 'i.!e ti4imrAose
1INF .1e o
Tv@i,ght to a 1/16-inch 017 of biroll is 1 .54 x 1/1S =-- 0 .090 60kes .
In
I
m4amphiAwbendIliw* tests, unon 'shich the dat@ . In table. 10 are !
sIliOINki6i llMirf121 0mado on sPec-Imens of floc same lengths, aid. it 7as fel t
desirable to Oaorrsine what left's:et, if any, the chasm) in length of th e
.', maximum 1usit load, the sloridor :aess ratio
.
column might WM. 7a.1
remaining! Impmbigat, IIIA4rl uaaels of three-pl , birch, all plies of the
mom. ialskIllislIMPTI gli rim IlMedaia, were made up fro'r veneer of the following
thicknesses : 1/30, 1/2d, 1/20, 1/16, 1/10 5 1/8, and. test columns varving
in length from 20 inches to 6 Isocline were it from t'oom and . tested . The
conclusion drawn from the3e tests is that for a given nlendernees rati o
the length of the column has little, if any, effect on. the maxim .um uni t
load which throo-e17 Mails Awl-.n will eustain . It is asourred]_ that th e
Game conclusion will a-e-1 s ti panels of other speciss .
IhO
_
"able 9, to whieh PprPriEgrChels-OlMeIr
made, p resents '
data by which it is Pos''PrIM.4p im 1011404
.
in t e nsion osF-plywood comnosed of various 10mds
ImWiO05 ;
Hof this table i s
identical with the corres p enlins columt et table I .
tolumn (e) is to b e
used in calculating the strea-th in tension of elywoo-i made uu of differen t
species . The method of calculation is based u pon the fact that the tensil e
Orength of rood in a direction peruendicu]ar to too grain ie very smal l
0Sm,ilsIxisAprwith_ that parallel to the grain and may, therefore, fo r
be ne g lected . 'o obtain the tensile strength
OVT-6=ns, timmi7 add to :otl:nr the tensile str e a e th, parallel to the
tlae indtVidual olie the ;rain of
lies parallel to the
the strength is desirree sample corn-Fa
.Gslsesk%r..,
_
-'
:,.
m
a- e l - 1-1
-rr
.
'I -
'
1.
r7,n '
_ -
1
II
1
I
'
f
~.
e, V
l ;-
'
I l an:4.
'
. 11
-
I
-LA
1
r„4 1
II
'I
1
~ .~
,~
11 I
The shearing strenzt1 of nl7 ao)d i s ) itT.sortance in conection with the design of box beams baying nl - w:oed c - ae n ee.es and for simila r
'
construction . Several series of tests are under wa s to determine t re
shearing strength of e1. woci of -.arione t icnneese ; when vnsnp)orted fo r
various distances . 7h1e tje .ie tests are not a .; yet corroleted, it i s
evident that it will net be nosoible to use a 1 hearing strength in calc,lating these members mach Treater than that of solid wood of the sam e
species . There is much more residual strength in -Ilywood after the firs t
failure than in solid wood, and for this reason a somewhat hiroher wor',hin g
stress would be .iustifioi . Until more data are availaele the ohoa r
allowed in plywood should not be over 25 per ce ::it greater than tha t
allowed in solid wood of the same epecies . This assivnrs that in th e
cheeks of horizontal beams the face plies w ill be vertical, a conditio n
dictated by experience to be best 'p ractice .
1 71-
l
:points i
Pl_ uoo
+ •L
1L
_
The matter of joints in p lywood is of the =greatest importanc e
in connection with the construction of various t-mes of built-up structure s
such as fusela=g es, boat b ,lls, nentoons, and beams and Birders . Several
series of tests have been male to determine the efficienc- of variou s
types of joint for different rinds of loading .
I
4
T
The fir s t series of tests was made ,r")en riveted joints designe d
tension and commree io :l . The tests were all ma d c in tension ; both
solid and hollow rivets wore use r . Two typos of test were r,n ; most o f
the tests en_; made on snocinen onl°- wile ono„ab to accommodate one rive t
(fig . 30a), . and later enough wide s p ecimens were tested (fig . 30b) t o
verify the assump tion that the data on the narrow s p ecimens could b e
ap p lied without correction to wider ones .
i'DY'
In general, most of t 1 e tests '"ere made on brtt joints, wit h
strap s on each side . In some cases the stra p s were of plywood and i n
others of galvanized sheet metal about 0 .0 inc'--es tick .
The nomenclatur e
used will become clear rn) exa m ination of fignr e
The first tests were .jade rnor_ red Ana pl'mvood cersnosed of thre e
plies of 1/13 material, riveted with solid copper rivets throngJ shootmetal cover nlatos . The rain of the face -)lies was nernendicular to th e
seam . Figure 31 shows the streneth off the joint •its-. varvi''g margins an
-a~ d
s p acing . It is apoarent that the best conditions are obtained with a
1-inch margin and a . one-half inch spacing .
4
11 .
(a )
Fig. 20.-(a) Test specimen for single rivet tsete. (h) Test specimen for muidpie-rust tests .
Sr+gz6So~ rS.6.;Yt D
al,Sca f.,bW.t .Fap.4dEvN.6.1.Y
Disye..s/&n65 . on'
Sa.s-itwc,kBau9'.,4wE r,A 7r
Fig . 1O.--Joints in the face veneer of three-ply wood .
5/ape
/in 20 to /1n 30
Strap, Scarf
S/a,oo
/in 20 to/in30
h ru s .tt
TnttllfllitltllltllllllllllIII
1fPIPI'lllllllilllllllllllrlllll i
I I F I l 111 FF l ilI 111 l 11 li 11 ltl l Fl 11 l lI II H II I I Fl lil 11 tt t l l liuusut ua . . n u
A/batros Scarf
Fig. 41.-Joints in plywood extending through the entire thieimese.
METHOD OF CUTT/N6 SC4 H'F
METHOD OPPRESS/N6 GLUED 3O/NT
Fig. 42.-Method of making plywood joints extending through entire thickness .
T
it
6
Plywood
h'e Shear rasr SF .c►nren .
Fig. 48.-Plywood glue shear test specimen.
1
. .__- _
60 0
f
i
1
~r
1
t
F
I
i I
~ j1
I
`~~~ .
1 (1
I
I
I
I I/
/00
i 1
11
1
0
z
t
/
ry
SPf'C/Nv OF RIVET5 //V %NC/1E. S
Fig 31 . -- Sing le-riveted brtt joints in plywood . Relations among
strength, margin, and spacing ; Fed gm', plywood, pliea 1/16 by 1/16 by 1/1 6
inch ; solid copper rivets, 0 .15 inch diameter ; sheet, .metal cover plates ;
grain of faces per p endicular to seam ; moisture, 7 .4 nor cent .
2 shows t
'variation of strength when axing a constan t
f
h and margins var yin . from one-~15arter inch to 2
ing
arly that no appreciable add i tiona l
'T very e
_es . mhT
;inn, the ' argin above 1 i~~cli . In fact ,
nt
th can
h
t in c
th ,gip of t'r_i face plies « ra : p arallel to th e
It wap ilospil
1-grartors inch wi thor t sacrificing
Ql,ld
be
roduccd
to #
*a MIOM
411
Fi?ur e
ne . .3
r
t
i
.5-00
7r
<
I
t
!~
.
__--.- ._ ..
~
f
_-_
_
0 25' 0.50
_ ._ _
! ._.___ .
075'
/vf,ti
/45-
/Oc)
'~i2' t
._
j;5Z)
' '
. .~. .
____
/.,?5-
.c70 0
Fi7 . M . ... tin_ le-t"ivetcd butt joitte in of '"ood . relation between strengtl and p ar in : S p acing 1/2 inch ; re'l par' nlynood, *l ies 1/1 6
by 1/16 bar 1/:l :6 inch ; solid corr_.er rivets, 0 .15 inch diameter ;
eet-meta l
co ' i'a
; grain on face ; neroendicUl r to seam' ; moisture, T~ p .4 per cent .
{
Sirlbar tests made on thre-e-p-lj'
c': eac. . ply oie-sixteent h
gave similar nesrits, as e own in si
'es 33 and 34 . With a margin o f
1 1/2 'anae e , the max mi n strength was vee,loe_7 . with a spacing of one-half inch .
bl.r
in,C11,,
R97
r
f0
0
i
-CF/ I
I-
-L
■
i
- 4----t._1_ .
.i
1- --
n
li
--A-
/
----!--.-.-.- ..--!--
_
._
/
/00
L
i
.
0'
O. 43 -
05-0
(I7'5
/oo
/At
';-4 3 . -- Single-riveted butt joints in n17v-ood . Relation be0Mn,siiL anrl snacing : T argin, 1 1/ 9, inches ; birch pl7rood, plie s
llw, ich ; solid copper rivets, 0 .15 inch diameter ; sheetmet440MINP!0WOW, 4tlst pre, 6_,6 per cent _
8
&4,5-
o 5n
/ oo
/ -y'
A.i4" ..q6./A/m/ //V(-/-f&-5
0.75
/ 50
/ 75
-Tqt.' *It -- Vitas-riveted' butt joints in
between strength and margin ; spacing, 1/2 tjseih ; b
by AhilJ4
.41011
,
Oipai.&, Sapp. iNiqm4r.i .16.15
camp .11WAIR-:7,11 mc3tstTITIop Ca !set Cent .
4.
The- margin could have been reduced to 1 inch off ` "en le '
I
witho
a great falling off in efficiency . Fi7ure 35 indicates. ¶t a syAcing o f
one-half
tneia
the hest with thinner birch (Bach ply 1/20 inch) 0.1.,
70 0
_
.-r-. .-7.
_
i
i
600
i
._ _
IN
~i ,
E
_
(1
-
,
...yo
/ EJ1 i
II/
c,
~
i,am
___
kJ,
I
i
\S.
1
_
_
'
0
/0 0
0 ?Lc5
IA/
/A/C,//5
sp4c/N6
0 50
Fig . 35 . -- Yultiple-riveted butt )int'l in oly-, oo :l ; relatio n
between strength
Spacing ; test joint, 5 to 5 1/2 inches icle ; margin ,
1 inch ; birch p l-oo ,3, plies 1/20 by 1/20 b ,r 1/20 inch ; solid copp e r
rivets, 0 .15 inch :1.i-lrileter ; :sheet-metal cover Plates : moisturc, 5 .6 per cent .
R973
Figures 36 and 37 show the strength of joints made in three ply birch (each ply one-twentieth of an inch) with five-eighths-inch
hollow aluminum rivets and plywood cover plates . A spacing of 1 1/4 inches
gave the best efficiency with a margin of 2 inches . It is possible tha t
greater strength could have been secured in the case of the specimen s
with the grain of the faces perpendicular to the seam had a greate r
margin than 2 inches been used . In the case of the specimens with th e
grain of the faces parallel to the scam a margin of 1 1/4 inches coul d
have been used without any great reduction in strength .
R973
-13a
700
600
y0
i
i t--
/0
0
0)00
ZOO
/, SD
2 00
449 RG/N' /iy / NC/yE. S
Fier . 36 . -- Sina'le-riveted butt joints in piy,9ood ; relation between strength and marlin ; soacinr*, 1 .25 inches birch -olyf4ood ., plie s
1/20 by 1/20 by 1/90 inch ; hollow alimiinrTn rivets, 5/9 inch optsid e
d.iam.eter ; plvevood cover plates ; rroisture, 5 .e per cent .
R973
0.50
700
600
0
cs
/00
/
INO
',
I
I
J
f
li
O
0,50
L00
/SO
.L7 0
,5/2/C//V6'//V /NC//ES
So
3. o0
Fig . 37 . -- Si g 7le-riveted butt ;joints in plywood ; relatio n
between strength and spacing ; margin, 2 inches ; birch plywood, plie s
1/20 by 1/20 by 1/20 inch ; hollow alininrrm rivets, 5/8 inch outsid e
diameter ; plywood cover plates ; moisture, 5 .6 per cent .
R973
5 4
c
1
eo
•
■r
'
__
w_ .
--- -
j
_ .__ ._
'
-
t -T
__ . _
A
f
NF
/
-
i
0.25
//
0.50
/
_
_
07.5"
/OCR
Si AC-/N6 /N /A/CH..E"S
.._ --J
/.2i
/SO
`tea .. 38 . -- Si n g le-riveted butt joints i?: 'Dlvwood ; ra'9m
twe1/20 stre-ng and spacing ; margin, 2 inches ; -b rch plywood, plies 1/20
by
by 20 inch ; hollow ai'minlr rivets 1/2 inch outside diameter ;
plywood cover plates ; 1roisture, 5 .5 per cent
.
TEe res
b
04ii .
&on three-' 1•r birch j eaciE r, 7 - one lea.{ ietE.
inch) with plywood cover p lates and one-half inch and three-eihths inc h
hollow alvmin'mn rivets respectively are -ol tted . in figures 38 and. 39 ,
These tests were made *ith margins ot , 2 inc? is . However, smaller margin s
egrid no doubt have been ='sed withort Op-,rec4 able loss in strength .
R973
700
boo
earl '
_
,
1
~~
44/
(Tale
!
:
-
. y)
i
1►
I!,
Boa
/ 03
,`,P4C/NG //V //I/C//E.5
Fig . 39 .-- Single-riveted butt joints in pl,- rood ; .relation )ettiaee n
strength and spacing ; margin, 2 inches ; birch t1 r^ood, plies 1/20 by 1/20 b y
1/20 i _ci_ ; hollor alp, rini m rivets, 3/3 inch o» .tsi de diameter ; p1 jnood cove r
elates ; moisture, 5 .6 per cont .
R973
rhea tLe most e =f =i:;c'irent spa i,ng and margin ane used, there i s
oTact-ically no difference in strength for the different sizes of rivet s
,investigated : `Towever, the smaller rivets require a smaller spacing an d
therefore more labor in manufacture . On ti-e other hand, the margin required is less than in . the case of the larger rivets, and this may i n
some cases be a d.ecid.ed advantage .
C;'btr
7i
m"d.;r
Or t1-yvroo.d, as preferre1. . If o f
y *01-nmi-n-urs shy about
-ty-fourths inch or o+ne-sit.xteent h
thiU.,&s, x
i- ended .f w'1 a thicknesses of p lyaaeod invesftgated .
rr .
he ei4i0fiIOpy ofe joints was determinec1 . by testing a numbe r
s of fife wood, both paralleland -perpend c - .lar to the fac e
ilk• was determined that osier the beet comd ,tions the efficienc y
of the joints with the face p lies pe rp endicular to the searaa wa:s. -about 3 0
per cent, while with the face olie .s parallel to t 4e sears the maximum
efficiency was a little over 50 p er feat .
W
4Mle-Tiveted joints may be satisfactory under certain circum - lr .
stances, ti--ey can :iot be used where an efficiency much over 50 per cen t
is required:. Ir these cases it is necessary to use glued joints, of which
. different typos .
Joints in Ind.ividu,al Plies .
Joints in individual Plies may bs
in a Variety of ways .
Figure 40 shows several possible methods ice'
pieces of veneer .
A considerable =Tiber of strength tests u p on s
,of' these joints have
been made . The simple
faint has been test
r a long range o f
slopes of scarf .
!ho
scarf joint, as wed as the diagonal but t
joint, have been testmaA e's• a ilones of the' diagonal . The sawtooth butt joint has been tested for various angles of the saw tooth .
In -balancing up the various factors of strength, ease of manufacture, and efficiency it was decided that the sample scarf joint is th e
~r
=
ple butt jio t gilkolae'
tile use d
O
,~tre
tisfact
.
• Carefull y
!R•
The Clore of the *MP, 'MI
.joint should 'be withi n
Unir
from 1 to Wt. 1
x
In comparison with the use of rivets, joints in individual plie s
are p robably more practical . They have an advantage, too, in that th e
joints in the p lies of a given panel may be staggered, so that any defec t
that nay occur in any particular joint only partially weakens the entir e
gs
time and labor involved in the p reparation of tits type o f
1 }
'ollpi lp, while probabl !'less than th .4ti-me and. labor *ivolved. in the prep'on of riveted Og4nts, is greater than that in preparing the scar f
t extending th
h f he ent'e thi
s of the panel .
i
i
r.
i'
i
U
Jo irten
ring
Entire T4i
If -
s s of Ply;'-
Vary 'tests"
been mode upon, OM* 'Dints extending through th e
entire thickness of a-100114 'Such'
red by various manufacturers using differerit7i
A at co-rbinat5tns of veneer thick"'wo types of scarf ,joint s
nesses and species, and various
extending through the entire plywood
Less have been tested an are her e
described as the straight scarf joint M tie :11batros scarf joint .
he
two tyres are shown in figure 41 . The tests is .
dicate q:ito conclus i .e1 y
that the straight scarf ioint is the superior joint of the two . An :kar, ination of the Albatros joint 'ill show that the face niy of the one pane l
coos not meet the face nl x, ofthe second- panel or on]-t *g ar+_ally meets it .
In p lace of being .gi .',ed to wood that 1-as the grain running in the sam e
direction, the face ,h]_ .. of one p anel is gln d to the core of the secon d
panel, in which the grain runs at right ar_Mles to the g rain in the face .
Joints in which the grain of the two nieces joined is at right an-le s
are not as strong as joints in which the grain of the two nieces is i:arallel .
Ted # #.W
the straig' : :_t scarf joint show that an efficienc y
Of FPO 90
cent 60p
obtained with this tvoe or joint for a slope o f
Melt de Wilt 1 ii 'p._
g,ccount 4t the variations in the effective ~~!
s,
recommended that a
f s ca
e r tha_ .i
hr
Oke neighborhood o f
_
VO‘O
416 25, with 6
P of 40:lp ulh S
recommended .
ti
fac
es
lig.mik
ft
meake
.ioi .
or '
ir, rlmai
op!'ler- due to sanding of th e
?u u
is of his hL that wer e
that; Wit
otnor1 away .
del lug Orel
tire
he face plie s
9bs4l
illgwb it*
th oit's
op Ohm We
4lbi! bf three-pty panels narali
cation o - the grain of th e
in tr~.e ,iokncss o the face plie s
iftel
ergot
a panel .
nsequently it is re 1NOO 0 the scavi'.int
that
be only lightl y
]
4r deem el* 4 ick
„y j. ;
face veneer .
emetON it is obvio s that a reduci
~
W
4* MIN,
1:Vfi'~'t 42 Trs400 ' °1 è ;re '':hod use3 ftAl- ct ing the scarf and fo r
gluing
two pieces of pl ;wood together . The beard . above the panel shoul d
be relatively massive and flat so as to distrnuto the pressure from th e
screws . ^'sro or three layere of blotting pa p er furnish sufficient padding
to accommodate irregularities in the surface .
R973
-15-
ve ing
In an effort to develop a substitute for linen for 4,r
w?iich could be used on present types of wing framework, sev' Differen t
kinds of thin plywood have been developed . llmon these are pl yrwoo . cornposed of three plies ~f
tenth inch, p lywook
a
r
veneer faces and metal wire cor e
faces, and several other types,
4
commercially possible to g lue up 14Mp
although the losses in maki ng t'610
than in makir comparatively till cil nl~ :n
* ac c
an d
she
th
en d.c cy
W O
N
was: ,pN found
rtt7
Light as clop :
r . Ti_
. **Woo
tr %Mich '72
,*
elusions drat TIM MEfallaw l
de
'GA
def
~t
t■u
rtI
1. Spanish cedar,
-A:aple '
black walnut, and
suf f
AmA 044w
consideration in p lywood air-plane wing coverilg es Si
r
2. These species may be glued satis
cu
¢
ucing the g lue between the p lies by means of t titlegi
with glue .
3. It does not Ds-on VANS
foot as did linen
'ev
O.
ora6edli
om a p
Z
I' - 1
trodg ate d
r.7
er p
oust
the same weight per squar e
tical scale .
1
4. Cerversrrg mOv 44her ve .nee,r or of a aam.4#.Im+ a
weer with
fabric, such as linen, cotton, -ire skedM r ; or ki 4 papa* . in orde r
is ,factor y
to be both practical from the point of vim ofcanufa*%ure
in mechanical properties
shown by test, we!
Pr , .S
, hreerptirn
as Muck a
.s loped line ;, :
5..
uhttligh.t
ii a0mbbOOmel prer-Saa.) f1
mane "ac`tur poss es flmm
is Ors. k
14ep
linen .
'M
of view o f
11op e
S . The thinnest ply-wood that am
O pr e
degree of facility (3 plies of one one-hundred-and-tenth inch
lacks toughness and tearing strength .
cede
s
7 . In .
the tea-inw strength of a practical thin plywood coverin g
is dcns.~y higher than that of doped
while its resistance t o
Mors as -'
sated by the toughness test is lower .
IMO
ti4l
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:
_
Sr
.
•
L
rtr
1r
1
.
'L.
t
L
, II
.
1
t II ' I . .
11L All I..I I =
IL . =L.'S II I
ar
IIJ
lEwJ
,
•
1 -1
..
A
_8 . In order'-el attain the requisite degree of , toughness, (014s necessar y
f i m.trod-rce a 411ci4ll tatiligOw
the construction, Grade A -kotton now i n
t .is 011I'Pose •
in airp lanDeOtruciftim
§a.g.e.f.a.ete,rg
ee
oped satisfactory tensil e
favorably with line n
Comb in a Mk"
_,/a* i kraf t pap er
strength,
Niilz' "ice 1.e-sghness . They compa
in tataTtialif -
2,
"1 1
thus far tested ,
'MOW With. 11 'ht wire
.00 Alp
'
a.:A
ffilMDun
point of vielci Of ensile strength
Jam. tearing resistaneit are not superio r
P mkt welPt . Tl*itr
tie' 'A** vi-rup 7.$uid aim.
w
I.Peae,w..
$6194gaiWt.1rarpsi
fie
11 . Obir.ONNpka
or
.. .
tUan 1*Vn‘ ,
a umftpii':.Iail*frrg
I- .
of Veneer gt*iVg ,,Weh is more rigi d
-
1-
L,l ,
1.
;mar° t*et by ,.at fist An eang es moisture V6!Wi#nf
rapidly and shrinks or ey-pams. wittl a cte.no-e in atmospheric humidity t-i th e
e..1t of .e•ithshoring an a-puree.i.alble loosening or as,minling a draw 'load.
t14tale, 415111■ Onttened a.Io.n.g the ■g''dgeS . A finish ofgoats of agar
.
east .
VM''P lat.TT--ely eltifwtew. veepid. change ii gun + q +'
-.L.:
ash
W9'tl'eg E
-
Od. .
=III I'
•
'.%,k have bee-a eomigIrted upon plyMed
ket-weave
fae-e's
te5crugated' sore . The faces *..e- wen 01 4
f spruc e
-made of
veneer I 1/S'P inches ride and 0 .017 inch thi4k,
GJ I
1
‘*gttiekt.es
s ove r
spruce 7/8 i a l e t h e s wide and 0 .018 inch thiet . The tom
all is al,relst 0 .2
; 141 ' 7 '
Ttiio f'oll owing conch r s i on .1,s,toslit7
it drawn froxtltetl0a!s : "high
I.Li.ti-d'it-y at
loads, tbt high tearing sure p
r_ mvarying
en
kn.leii(iriiII44K.0 3 And Corp natively high toughness. rode
that v . 1 W .
;,I I
p lywoo.6 to ubea, ray
a very de-sirable material for' -Ow.gOii, 0
a inlaYgON
: 5
Data etnIcernins; e:,111nIs for ply-wand will liae f'sIvA
under the general headily, "Glues ."
. I 6.
-=
the
on .
text
11
The folloritg specification fzgl-r wctt.t.rvr;o:of pl-,oofi is based upo n
streng th tests just described and upon the glue tests- presented farthe r
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Specification for. „rater-resistant Veneer Panels or Plywood .
General .
on of vial, issued by th e
i~ General spate .
fow
gy
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54 *5;4.14 opening of bids ,
of
Construction
and
Ttepai
t0pPNku
1 .l form part of these specifie5t1O .N .
tv + i etre' t'1
. hater-reeis!tabt
'tsY
g
r ents f 'W veneer p anels fo r
od. is specified .
1'ateria l
3 . le following species of wood may be usrela : in plywood i nstruction :
Ras ;wood .
Na hogany(true and African)
B-' Ple (hard and soft) .
Birch .
Redwood .
Cherry .
Spanish cedar .
Fir ( ;rand,noble,or silver) .Spruce .
. Walnut .
Western hemlock, '
White elm .
White pine .
Yellow poplar .
4 Other s p ecies of wood shall not be used without the writte n
Q1OWPval of the Bureau of Construction and Repair .
tdem --
The veneer must be sound ;, clear, smooth, well-marunc
factured_ stock, of tniform triokness and free from injurious defects .
Sap strew=s and sound Din knots will not be considered defects .
colo.ra-ti:or will be allowed .
6.
IOA v
wmr at be rotary cwt, sliced, or sawed .
7. Thickness .
Unless otherwise specified, no single -sly of venee r
shall be thicker than 1/12 inch . I;i thhe.e-ply s.to . •the thickness of th e
core my $t be bet:. ee=n 40 and 75 pe', .cent of t i+e tatuli thickness of th e
in thickness .
plywoo• ., exz ept f'Or panels 6tne-sixteenth in &h Or
lat
8. G
meet the
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VU~i•-''E-
-- Any glue Or dement to
in parag+rap1ss 20 and . 21 .
-b'1e
used ,w
li Oil l
9. Grain . -- The train in each ply shall
'Ai. ri:= ht angles t o
grain in the adjacent p lies unless otherwi &e wtat t. 'ate the order .
10 . . ) anufac
density wood and f
specifically stated it tl
R97 3
'5 tie,' lit soft or lowWilma Mir
otherwis e
h!.l4-dyer wood -en
.several plies, , .
ax' er ;
'fae core may be mad
'
in which case the gain of the adjacent plies must, be perpendicular .
The plies must be securely glued together, after which the plywood mus t
remain flat and free from blisters, wrinkle-, lau -p ing, checks, and othe r
defects . Plywood manufactured with cold glue must remain in the p ress o r
retaining clamps . not less than three hours .
11 . Joints . - - Plywood 10 inches wide or less shall, have faces made o f
one-niece stock . In order to conserve t} :e narrow widths of veneer ,
accurately made edge ,joints will be allowed in the faces and cores of wide r
stock, but the number of joints permitted in any - :ly shall not exceed . the
width of the panel, in inches, divided by eight . Edge joints are joint s
running narallel to the grain of the plies joined . All r_,lv,ooa built o f
jointed stock must be so constructed that all joints are staggered at leas t
1 inch .
12 . In panels over 8 feet long scarf joints will be permitted ; th e
smaller anele of the scarf shall have a slope of less than 1 in 25 . Scar f
joints in adjacent plies must be staggered . Scarf ,joints are joints i n
which the seam runs across the p ly at right angles to the `rain .
13, Butt joints will not be permitted .
14 . In case the core or croosband.ing is taned at joints only unsize d
perforated cloth Mane or oven-mesh unsized cloth tape apulied with rater proof glue or cement shall be used .
15, Noisture content. . - - The finished plywood shall be dried to a
moisture content of 9 to 11 per cent, with a tolerance of plus or minu s
2 per cent, before it is ship p ed from the manufacturer's plant . The equalization of moisture shall be effected by kiln drying, followed by con ditioning .
16. Kiln drvine . -- The panels must be piled and placed in dry kiln s
as soon as possible after being released from the press . The method o f
piling must be apuroved by the Bureau of Construction and Pepair . Afte r
the stacking is complete?._ the panels shall be properly weighted to preven t
warping during the drying process .
mho best results in the kiln ar e
obtained with a temperature of from 95° to 115° F . and a humidity ranging
from 50 to 60 per cent, decoending upon the thickness of plywood and numbe r
of plies . The circulation must be maintained at all times .
17. Conditionin g . -- All panels must be conditioned before fabricatio n
or shipment . The conditioning shall be done indoors under tem p erature an d
humidity conditions existing in the factory for a period of not less tha n
24 hours for three- p ly panels one-eighth inch thick and . proportionatel y
longer for thicker stock . The piling and weighting shall be the same a s
specified for dry-kiln stacks .
18. Cutting . --- Cutting for leneth and width shall be full and true .
The veneer shall be cut to the thickness desired in the finished plywood and
any overallowance on this thickness for the sanding operation is very undesirable .
-19-
1~ . Finish . -- In all cases the tar p m~~st be removed from the face s
of the panel, and., unless otl:er5; iee s p ecified in the order, the plywoo d
shall be lightly sanded to a, smooth finish free from defects .
20, Submission of samples fortest . -- The manufacturer shall submi t
to the Bureau of Construction and Repair for test 20 samples, each 1 foo t
square, of the oly ood which he proposes to furnish to airp lane manufacturers .
21. Boilingor soakingtest .-- The waterproof q„ali ty of the glue shal l
be tested either his boiling in water for a p eriod of eight hours or b y
soaking in water at room temperature for a period of 10 days . After boil ing or soaking the samples shall be dried at a temperature hot exceedin g
150 0 F . to a 10 per cent moisture content . Tile plies must not separat e
when the sample panels are su?ojcctod to this test .
22. Sheertest . -- The strenPth of the glue shall be tested in fiv e
test specimens cut from a sample pane-i . The form of the test specimen i s
shown in figure 43 . The ond'_s of the s p eciment shall be gripped in th e
jaws of a tension-testing machine and the load aprlied at a speed of los s
than one-half inch per minute . The glued surface must not fail at a loa d
of less than 150 pounds per square inch .
23. Approved .list . -- Nanufacturers whose ps;vwood does not compl y
with these specifications will not be considered in awarding of Contracts .
The list of manufacturers whose product has satisfactorily pas,od the
tests outlined in paragraphs 20 and 21 may be procured from the Burea u
of eonstSuction and Repair, Navy Department, Washington, D . C .
Inspection .
24. Unless otherwise stated, all veneer and plywood shall
d at the plywood manu.facturer t s plant .
.e in_spect-
25. The inspector shall make the tests specified in paragraphs 21 and
22 on at least one sample panel from each orees for each eight-hours ! run .
26. In case the plywood fails to meet the soaking and she .,: tests i t
shall be rejected .
If the glue fails to meet one of these tests bu t
passes the other, the test in which it fails must be repeated c 7 not les s
than twice the original number of specimens selected taken fros two o r
more panels .
If the glue fails to pass the second test, the ? '.ywoe d
represented by the samples gust be rejected .
27 . In case of consistent failure or lack of r4iformity in product ,
the manufacturer will be required to submit a detailed written statemen t
giving the following information :
: The composition of the glue and the correct practice i n
(a)
mixing it .
(b) The maximum time between mixing and apply-ing the glue .
(c) The exact procedure in applying the glue and in pressin g
and curing the plyeood and such other details as the Inspection Department may direct .
The ins p ector shall see that thereafter this schedule is observed .
28 . The inspector shall have free access to all parts of the plant s
were the plywood is being manufactured and shall be afforded ever y
reasonable facility for inspecting the materials used, the methods o f
manufacture, and the finished p lywood .
Packing and Shia-miner .
29 . Plywood which ha :- passed inspection shall be packod in crate s
which will protect all edges and surfaces from injury during shipment .
Ordering .
30 . To facilitate the execution of contracts the order will stat e
any special requirements which this material must meet . The order shal l
state the number of pieces, the width across the grain in inches, th e
length with the grain in inches, the thickness of the plywood and th e
individual plies, the number of bliss, and the species of wood to be use d
for faces (to be marked "Faces"), for core (to be marked "Core"), and fo r
cross-banding (to be marked "Crrssba'nd"), Sizes riven shall be finishe d
sizes and shall conform to commercial sizes when p racticable . The orde r
shall also bear the specification number .