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Northrop, E. B.; Chittenden, H. A., Jr. (ed.) / The Wisconsin lumberman, devoted to the lumbering interests of the northwest
(July, 1874)

Classification of wood,   pp. 393-397 PDF (1.8 MB)


Page 396


The Wisconsin Lumbernan.
grain, and is diminished by wetness
and increased by dryness. Very few
exact experiments have been made
upon it. Its smallness in pine-wood,
as compared with leaf-wood, forms a
marked distinction between those
two classes of timber, the proportion
which it bears to the tenacity along
the grain having been found to be,
by some experiments-
In pine-wood, from 1-20th to 1
1-10th.
In leaf-wood, from 1-6th to 14th
and upwards.
II. The Resistance to Shearing, by
sliding of the fibres on each other,
is the same, or nearly the same, with
the tenacity across the grain.
III. The Resistance to Crushing
along the grain, depending, as it
does, on the resistance of the fibres
to being crippled, or "upset," and
split asunder, is greatest when their
lateral adhesion is greatest, and was
found by Mr. Hodgkinson to be
nearly twice as great for dry timber
as for the same timber in the green
state. In most kinds of timber,
when dry, it ranges from one-half to
two-thirds of the tenacity.
Experiments have been made on
the crushing of timber across the
graiL, which takes place by a sort of
shearing; but they have not led to
any precise result, except that tim-
ber in general is both more com-
pressible and weaker against a trans-
verse than against a longitudinal
pressure; and, consequently, that in-
tense transverse compression of pie-
ces of timber ought to be avoided.
Certain special kirds of timber are
valued for the property of resisting
compression across the grain well.
Of these the most generally used is
lignuni-vitse.
USE OF WOOD IN MACnqNERY.-The
following statement as to the more
ordinary kinds of wood, according
to the purposes in machinery to
which they are applicable, is princi-
pally based on a similar table given
by Holtzapffel in his treatise on Me-
chanical Maniptdation.
Fon FRmEWwoRK -Mahogany is
strong, stiff, durable, and free from
warping. Pine and deal are strong
longitudinally, stift, and straight-
grained. Oak, teak, and saul, are
strong, tough and durable. Ash in
tough and pliable. Elm (durable
when wet), and beech are strong
against pressure.
Fon LEvERs AND COXNECTDIn-RODS-
Pine, deal, and mahogany are strong
and stiff. Oak and teak are strong
and tough. Ash, hazel, hickory, and
lancewood, are tough and pliable.
Lignum-vitme, box, and mahogany
are used for pulleys, sheaves, rollers.
Box, beech, holly, lignum-vitte, and
elm, are used for bearings for shafts.
When wood is used for bearings, the
ends of the fibres should be exposed
to the pressure. Crabtree, hornbeam,
locust, and beech, are used for cogs.
Deal, mahogany, pine, and alder, are
used for patterns.
In machinery whose speed is liable
to be suddenly changed or checked,
it is often useful to make some of the
parts, which transmit the motion, of
wood, although the whole of the re-
mainder may be of iron; the object
being that the wood, by yielding to a
shock, may prevent it from damaging
the iron; and also that in the event
of breakage occuring, it may take
place in the wooden parts, which can
be replaced more easily and at a less
cost than the iron parts.
For example, the great spur fly-
wheel, by means of which a steam
engine or a water-wheel drives the
machinery of a mill, is very generally
a mortis-wheel ; that is to say, a cast-
iron wheel with rectangular sockets
called morties in its rim, into which
are fitted wooden teeth called cogs.
The pinion which those teeth drive
is wholly of cast-iron. Wooden cogs
are made double the thickness of
cast-iron teeth that have to bear the
same pressure.
Another instance of the applica-
tion of the same principle is when,
in a steam engine that drives an iron
rolling mill, the middle part of the
396


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