THE GLUING OF WOOD 
45 
the species tested. The wood failure and the shear strength of the 
glue joints tested have a distinct relation to the specific gravity 
of the wood glued. The conformity to this general rule is closer 
where the results obtained with the three glues are averaged than 
where they are taken individually. The variation from this rule 
for certain woods is due to other factors, which are discussed below. 
The increase in the shear strength with the specific gravity of the 
different species is similar to that for solid wood (38), and under 
good gluing conditions the joint strengths are not seriously affected 
Species' 
Poplar, yellow (Linodendron tulipifera)L. 
Chestnut (Castanea dentataji. __ 
Fednood. (Sequoia semper y/rens)£ _ 
Cedar-, ivesfer-n red (Thuja plicata)£ 
Hemlock, western (Tsuqa heterophyl/a)— 
Fir white (Abies concolor)t 
Gum, red (sapwood) (Liquidambar styracifluo)— 
Pine, northern white (Pmus strobus) 
Cottonwood (PopuluS Sp)!— 
Butternut (Juqlang cingrea)L 
■Spruce. Sitka (PlCeq iitrhonili) 4 
Pouqlas fir (Pseudotfuqcf taxifolia)i. 
Blm. American (Ulmus amencona)! 
Alder, red (Alnus rubro)L 
Cypress, southern (Taxodlum disfichum)!^- 
Sycamore (P/atanus occidentolis)— 
Blm, rock (Ulmus racemosaXf. 
Mahoaanu (Swiefenia sp)L 
Maqnclia (Maqnot/a sp.) , 
Pine, southern yellow (Pinus sp.)— 
Basstvood (Tilla sp)— 
Pecan (H/corja pecan )£. . 
Sassafras (Sassafras vanifo/wm)— 
Pine, western yellow (P/nus ponderosa)— 
Maple, soft (commercial) (Acer sp)!— 
Gum, red (heartwood) (Liquidambar' styraciflua)L 
Gum. black (commercial) (tlyssa sp)* 
Oak, white (commercial) (Quercus sp)*- 
rvdlnut black (Juqlans niqra)t. 
Gum. Apelo (commercial) (Nyssa sp.)'!. 
Oak. red (commercial) (Quercus sp)£. 
Beech (Faqus qrandifolia)— 
Cedar , eastern red (Juntperus yirqiniana) 
Cherry, black (Prunus serotma)L 
Maple, suqar* (Acer saccharum)! 
Birch, yellorr (Betu/a lutea)? 
Cedar. Alaska (Chamaecyparis nootkatensis) 
Ash. white (commercial) (Fraxmus sp) 
Osaqe-oranqe (Toxylon pomiferum) 
Persimmon (Piospyros virqmiana) 
ttickoru (Hicoria sp)L 
/■Cpmmon and scientific names are the standard 
2-tfcdrt~ood 
d-Mostlu heartwood 
A NIMAL 
Wood Failure -Per Cent 6 
■mull 
x 
SSopwood 
apwood 
of identified 
ttmaled proportio 
of joints 19 not comparable with 
in the test methods and specimens 
the softwood or non porous class ; 
U5.PcptAyr.Misc.Circ.Sl except those designated 'X commercial) 
belong 
Figure 14. — Results of tests on joints of various woods glued with animal glue under 
good gluing conditions. Values shown are averages of 30 to 180 specimens 
by the percentage of wood failure developed in test. This indicates 
the impracticability of judging the strength of joints on the type of 
failure alone. 29 
Hardwoods (porous woods) as a class require more care in gluing 
than softwoods (nonporous woods). This difference is most apparent 
with thin glue, for example, a warm animal glue may penetrate exces- 
sively into the porous woods and thus give starved joints. Figure 16 
shows the results of tests made with animal srlue under starved- 
29 In commercial work a rough measure of a good joint is whether or not it is stronger 
than the wood. If, when the joint is broken, the break occurs mostly in the wood the 
glue joint is considered entirely successful, but if the break is mostly in the glue the joint 
is not ordinarily considered entirely satisfactory, regardless of the force required to break 
it. With such a measure of quality much depends upon the strength of the wood, and 
there is consequently great danger of misjudging the real strength of the joint. 
