44 
joint strengths obtained. In many species the percentages of wood 
failure is considerably less than 100 per cent, and in such cases the 
joint strengths must also be considered in determining the success 
obtained. The strength of the joints in most species is equal to or 
greater than the calculated strength of the wood itself. 
The relative positions of the different species with respect to wood 
failure developed in these tests vary with the different glues, but in 
general they are similar. Woods of low joint strength, such as Sitka 
spruce, western hemlock, and redwood, show a high percentage of 
wood failure, and woods of high joint strength, such as sugar maple, 
CASEIN GLUE 
Species ' 
Wood Failure Per Cent 6 Shear- Strength —Lbs. per Jq. In7 
20 40 60 60 100 1000 ' . 2000 " 3000 
Ppdwnnrf (Spaunia ipmnprvirpn.i)* « 
Cprlnr we.ifern red (Thuia nlirafn-) 2 » 
Fir tvhitp (Ahiai rnnrnlnr) 4 to 
Snrurp Sdka (Pirpa .iitrhpn.il.il 4 ® 
'V'o" xnij+hBrn (Tnyndium di.i+irhum\ 4 ® 
Hemlnrk wpilprn CT.luijn hplprnphij l/n) 4 ® 
rpdar ens fern rpd (.luntn/tr-jx vir/ji'mana) 4 ® 
rhei+nul ( V"W/i»M dpnlntn) 2 
Alder rod (A/nul ruhm) 2 
PmP nnrlhprn while. (Pm/j.l ilrnhui) 4 ® 
Mnntnnlia (Mnnnnl/'/v .in J 
Flm Ampnmn (lllrnux nrnpr-imnr,) 4 
Pine western ye/low (Pmus ponder'oso) 4 ® 
P/ne. southern- ye/low (P/nus sp ) §L 
Cottonwood (Popu/us sp) 4 
Gum tuneln (rnmmpmnl) f/l/yisa an} 4 
Gum, red (Sapwood) (Liauidamhar styroaflua) 
Poplar, yellow. (Liriodendron tul/pifero) 2 
^iimmnrp 1 Pfnfrtn/j 1 nnridenlsr/n) 
l^um hlnrk (mryiwiprri/jl) (Nylin- ip ) 4 
- 
F 
= 
» 
= 
Elm. rock (Ulmus racemosa)* 
RultprniA (li/ij/n-nl rmprpn-) 2 
rhornj hlnrk (Pn,n,j1 iern+mn\ 2 
Mnhnijnny (.'ivviolpm'n in) £ 
Dnuryln.l fir ( Pl<o„dsifiun-n- tanfn/m) 2 
Ppran fliirnria nemn ) 2 
Cedar, A/oska (Chomaecyparis nootkat&nsis)— ® 
Gum, red (Hear f wood) (Liqu/dambar styraciflua)— 
Hnk rprJ rrnmmemnn (Ouor-m,i in) 2 
Sassafras (Sassafras Yar/ifolium) 3 
Maple, soft (commercial) (Acer* sp) 4 
Wrrlni/t hlark (.lii/jlanl ni/jrn) 2 
Rpprh (Fnriui /jrnndifnlln) 4 
Oak white (commercial) (Quercus sp) 2 
A in white (cnmmpmnj) (Ff/yy/mjx in) 4 
R/illwnnd (Tilia in ) 4 
Rirrh ijellnw (Refuln hfi-pa) 4 
Perlimmnn (Dinmyrn'! virijinmnn) 1 
lUnple .lu/j/rr (Acer mrrhrtrum ) 
Hirknry ( Hirnrin- in ) ' 
\ 
- 
a 
: 
/■Common and SCtGt 
2- Hear t wood 
3- Mostly hear f wood 
4- Meant wood and Saprtood mixed on not 
SSapwood r 
fa-Wood failure pen cent indicates. Jhe est 
names ane the standard names 
USPept Aqn. Mtsc Ore. 92 except those desiqnated'fe 
1-7he shean strenath ot joints is not comparable with the shear st /-en at h of sol/d wood, pub/* shed 
to differences in the test methods and specimens used 
Q*lndicates woods of the softwood or n&nporous class • others belong to the hardwood c 
proportion of the joint area of the specimen where wood fibers were torn awoy 
t US Pept Aqr. &uj. sss and elserrrere.o 
porous class 
Figure 13. 
-Results of tests on joints of various woods glued with casein glue. 
Values shown are averages of 60 to 240 specimens 
persimmon, and white ash, show a low percentage of wood failure. 
For any one glue, the woods giving similar joint strengths vary con- 
siderably in the amount of wood failure, and those with lower per- 
centages of wood failure, therefore, require more care in gluing to 
obtain the full strength of the wood. 
RELATION OF DENSITY OF WOOD TO GLUING PROPERTIES 
The density of wood has a rather close relation to its gluing prop- 
erties. This is illustrated in Figure 15, in which the results of the 
tests described on page 42 and shown in Figures 12, 13, and 14 
are averaged and plotted against the average specific gravity of 
