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A iAPIDI MIETI-IDi OFr IDIETIEIPAININ4 TI-iE
SPECIFIC GIAVITY OF VENEIE
SCIHOOi OF FO.RSIRy IIBR4R
UNIVERSITY OF WLU' DA
i, U S DU
E'*-. .' "
This Report is One of a Series
Issued In Cooperation with the
AIRCRAFT VDUESI6N CRITtRIIA
Under the SIupervision of the
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST PRODUCTS LABORATORY
In Cooperation with the University of Wisconsin
A RAPID I-.THOD OF DT2,i'I':I::- r.E $SECIFIC GRAVITY OF V,.-Err-
B3ELS0OT H. PAUL, Senior Silviculturist
JOE.: P. LIIBACH, Assistant Forest Products Technologist
A raid method of determining the specific gravity of veneer has been
developed. A sample of veneer is accurately cut with an ordinary paper trim-
mer to 100 square centimeters- (10.0 by 10.0 centimeters) or 50 square centi-
meters (7.07 by 7.07 centimeters) depending upon its thickness. The thick-
ness of the veneer is measured by a .iicrometer to 0.001 of an inch. The
veneer is then attached to a sensitive spring of the type used in a Jolly
balance, an, a chart is read directly in specific gravity for the given
thickness of veneer employed. Parallel readings for allowable tolerances of
thickness are included. The specific gravity of the sample at the current
moisture content- is read directly from the chart. If the veneer is oven
dry, the specific gravity will thus be read directly from the chart. For
veneer at a moisture content below the fiber-saturation point, a simple con-
version from current specific gravity to an oven-dry weight and oven-dry
volume basis may be made by subtracting the product of a constant and the
pe..cent of moisture. Such constants for each species and for groups of
species are given.
Equipment and Use
The equipment required consists of:
1. A aperer trimmer with adjustable stop to cut the veneer samples to
size. T:,e trimmer is modified as shown by providing a guide and a piece of
sandpaper :lued to the trimmer surface to hold the veneer firm (fig. 1).
'This mimeo-r- .ph is one of a series of progress reports prepared by the
Forest Products Laboratory to further the I1ation's war effort. Results
here reported are preliminary and ,,a"' be revised as additional data become
-One inch equals 2.54 centimeters.
-41oisture content may be determined accord ir.gn to Ar-.yv-Tavy Specification
A-'-., or by means of an electrical moisture meter suitable for use with
Mi l.eo. -To. 13)? 7
2. A mi-'ometer ,"aliper to measure veneer thickness (fig. i).
3. A -awe consistin0-: of a steel pla*e 10 by 7,07 by 0.16 centimeters,
or 3. \ 21. by 0.0' inches (fi-. ) The -,age is used to set the triL-mer
Stop for cutti: sa-mples of either ICC or 50 square centimieterc surface area.
A ru'le :'-,:Tp to 0.01 inch or to 0.02 centimeter.- may be used in the
absence of a rnpared steel plate -age. Cut veneer sample at a sain.t a.
*, A sensitive helical spring, of the type used in a Jolly b-lance,
havi:..' an elo;. -tion of about 5 centimeter per gram within a ran-Ee of a-.cut
9 :ra-..... e .r:.r;- can be puchaced from s-ientific equipper.: s-pply ?.cu-.es
at a very nominal cost.
5. A stror.r, piece of thread. Cne e..d of this headd is tiedi to t'-e
.pri:'.., and a paper clip is fastened to the o'her er.j. -he parer cl-'. is ue'
to attach the veneer samples to The thread. The thread carries an. i.d: cat r-r
which should rc- chec',:ed frequently at zero chart readir.,. .-he indicator La:
be a horizontal line on a s..all piecec e of paper faste.e:.ed to the thread through
two holes so that it can be slid up or down.
6. A suitable support from which the spring can be suspe:.ded, ar.d .,o:.
which 4'.c -pecific :gravity chart may be fastened.' TLis supoi,'t La.y have a
base i';ith three levelir.;- screws, or the spri.,-; and chart may be suspended "y
minis of screw-eyes driven into a wall, in ".'hlch ever.t the diamLeter of the
screw-ey, should be slightly larger than that of the siri:". ".-.ere a ,:wil is
not nv !L.ble, :.e screw-eyes ::mar be driven into a flat board t?:t is t ,ea-
s c::,e'.2ed. from above.
7. A 5-.-r-im wei-ht,., to be ".ied in 'd.ust:. the elon -ation of t.e
sprrn..: to t`e :je-ific gravity chart.
8. A specific -,ravlty chart. (This chart, devised by txe Fore:t
products Laborator.y, miay be detached from this report and mounted for :s.P.)
SCalibrn-ticr. of the S4ri..'
Ad.'u.t the elor.:n.tion of the spri:.g to the -oetific ;-rayv'. chart by
inter'e, ti:.c: the correct s'-,-,nsion prcint of t.e "pr-:.;: (ft. 3). s-.is pcInt
can be found *-..'erimentall" as follows: Pla:-c the saall e.d of the spri'.,
throu'1 the p_.orti.'.r: screvw-eye (or otner s'.:ucrt) -;.d insert a thin strip
of metal (an old razor blade will serve) over the screw-eye and ir.nto a coil
rear the extremity of t.e spri:.,-. "th the r'u-re cli in pla.'e, set the zero
line of the weight s'-le (shown cn the ri-. t sid- of The v-e'ific gravity
chart) under the indicator. Fasten the .-.-raj: weight 1o the paper clip -ard
note where the indicator falls on the weight -,_Rle. If the indicator is
c' r" ed I;:. Fh --ra _rk I-ov --' e
c~-r.ed. :*t t --ra-n .sark, remove c --r:. wei-ht a:.d shorten :he ef-
fective vl ::..* of the sprirc by intercepti.r.,> it farther dce.. wit. t.e metal
strip, -:.;set the i. :.-i'tor on zero nrd .ci:. :.ote the d: splare:e:.t made by
the 5- rr.. ei:t, -:.epeat this )ro-ed-ire until the weight displaces t?.e
spring just the right amount to bring the indicator from the zero point to
the 5-grai line.
It is a =ood plan to insure agair.st the sprirg being overloaded by
placr.ng a smaller screi/-eye under the spring at the point beyond which it
should iot be stret-hed. If the suspension thread is then passed through this
screw-eye, the spring will not be elongated beyond this point.
Procedure to Find Specific Gravity of Veneer
1. Set the paper-trimmer stop with the steel plate gage (fig. l) and
cut the veneer p' ple to size (fig. 2). (Samples will have a square surface.
Use 100l-suare-centimeter samples for veneers of average density and of thin
to medium thickness; use 50-square-centimeter samples for very heavy woods or
thick veneers. This precaution is taken to prevent overloading of the helical
2. Obtain the average thickness of the sample with the micrometer,
select the proper thickness line on the spe-ific gravity chart, and .adjust
the chart so that the selected line is back of the vertical thread.
3. Adjust the zero line of the chart to the indicator on the thread.
4. Attach the veneer sample to the paper clip on the thread and read
the specific -r!;vity as registered by the indicator on the thread (fig. 4).
('T"hen the sample is 50 square centimeters in surface area, the specific
gravity reading will have to be multiplied by 2.) If the sample is oven dry,
the specific gravity of a 100-square-centimeter sample is thus obtained with-
5s If the sample is not oven dry, correct the specific gravity from
current volume and moisture content below fiber saturation point to an oven-
dry weight and oven-dry volume basis by use of the following:
Specific gravity equals chart reading at X-percent moisture content
minus KX, where K is a constant for each change of 1 percent in
moisture content for a .'.ven species.
'rcraft woods listed in Army-.avy Aeronautical Specification Plywood
and Veneer, ,o. A.T- 7T.T-P-bllb, have the following values of K:
Mineo. So. 1397
AlT-i.ka tir'h, bas.wcod 0., IC
A',-ican beech, paper birchr. .CCIO
j,.,c t j .CC12
-;.'-ri^Lr. el.T, white splruce .C 13
..cble fir, zweet bir'h., ,'ellcw birch .C014
3 ,.,r zaple, 'ellr',j.cplar .C0l6
ed :..le, red :,'.ruce, water tuLelo .,Cc18
Sitka si.ruce, southern Mai.nolia, black -,!alnu.t .CC19
c.,,l;-s-fir, pecan, silver rzaple, wes.er:. hemlock -C'C
ro..:.erosa pine, tort C'rford white-.'edar .CC21
3 .'r pine .(.'22
Redwood '- i
:'.i.ayva (so-called African mahogar.y) .L2"
:ici :c---. (from Tropical America) CJ
''or -_.T'proin.ate values the consta..t ra;r be ro-.:.dedi to the ..earest di-4it
in the third deci-al place, as 0.C01, 0.C 2, '-'.d O.C. .
7se of Chart for Other Thicknesses of Ve.neer
For veneer in thickliesses of 0.014 to O.,21'l inch:
spendd a sample 100 square centimeters in surfac,-e area on the 1.i. of
the chart representing twice its actual thickness, o:..i lo-uble the
reading to obtain the correct specific -ravit..
For veneer in thicknesses of 0.C6 to O.C:- inch:
S---. e..d a .'...ple 5C' sI--.are centimeters inr. surfa-te area on "he lir.e
represeiti:.,- half its thick.ness, and read --ecific -rjvity d'-tl;-
from the chart.
Inprertion Frc-eduire for Ruli'.,: Out Light ateri.l
In some 1r.".]'ie actions, trhe ob.:tc/t is to ascertain that '.c Fpe-fic
gravity of the wood selected does not fall below a .-er ':a-. a c nt, .i it is
not the actual determination of the z.e'ific Fl-vi ty of each ;L.le th't. i
sou-:.t. In these ,stances, it i! possible to shorten still rther the .-
cpe:tion .jroced':re, as follows-:
1. . the ve..ecr .1i...olo to size.
.. ?romrn the sI:ccifications determine the .:.axia'. thickness to b .e .ealt
with in tie tolerr...-e ra,.
thickness scale of the specific gravity chart for this thickness back of the
thread and note the passing mark (least pascir.;; specific ,,ravity mark, cor-
rected for moisture content when necessary) on the chart. Assume that all
pieces registering an equal or greater value than this are acceptable. -'.he
pieces that do not pull the indicator down to the passing mark may be de-
ficient in thickness and, after being calipered, they still riLay be acceptable
if they reach the passing .:Lark for their particular thickness. This leaves
only a fraction of the total number of pieces to be calipered, thus saving
time in inspection.
Mimeo. ::o. 1397
Sandpaper ,slued to trimmer
Knife. edge it mid- /
point of jage.
I~ ~ ~ (- .1
Wi 't: -are
Ad~j-usn"table trl~nr stop
'. ,2B FI
Figure 1.--Equipment to cut and mneas,.,-e veneer samples. The trimmer
stop is set with the gage to control size of veneer sample.
Cut veneer sample
away from grain
4 &6529 Yr
' Wood block to hold
Figure 2.--Cutting the veneer sample to size.
Fi7-.re 3.--Methol of calibrating spring.
Figure 4.--Determining specific gravity of veneer.
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IS4 .36 :U_
SPECIFIC GRAVITY CK&R
FOR VENEER SPECIMENS-OF AREA
AND THICKNESSES SHOWN
VM(M ,TRICI M XXC
SPROIFIC GRAVITY CHART- S4
FOR Vasm NPUTMENS OF AREA
AND TRrCXNKSSZS SHOWN
JfiIVERW itY Of FLORIDA *V 8
3 1262 08866 6051