of mouth in a plane is an important, if not the chief factor in
the production of smooth surfaces. That part of the body of the
stock and the sole immediately in front of the cutting edge
exercises a compressing influence on the tissues about to be
cut, and so hinders the leverage mentioned from taking effect.
Thus it is evident that a wide mouth in a plane, whether due to
legitimate wear or to an erroneous method of remedying clogging,
is not conducive to smooth, clean work.
has been stated in the section treating of timber, even seasoned
woods are liable, under alternating changes of atmospheric
dryness and humidity, to alter in form. Beech wood is no
exception. This must be guarded against as far as possible, and
all new planes before being used should have their stocks and
wedges well saturated with raw linseed oil.
The effect is to limit hygrometric
influences, and so to prevent warping, to harden the sole, and
to cause the plane to work much more easily. Various methods of
causing oil to permeate the wood are adopted.
That least to be recommended is
rubbing the sole over with an oily rag; and another method,
sometimes recommended, of placing the sole in a shallow tray
with the oil about 1/8" deep, is hardly much better.
The carpenter's rule-of thumb
method of plugging the mouth and filling the throat with oil
has, indeed, a modern scientific basis to support it.
The experiments of Fr. Elfsing, as
set forth in his "Uber die Wasserleitung im Holz," published in
1882, prove that the permeability of timber is least in the line
of a radial direction (that is, from the sole of the plane
upwards), slightly greater in a line parallel to a tangent to
the annual ring, and greatest in a line parallel to the axis of
the stem (that is, from fore end to heel).
Though the plunging overhead in oil
is effectual, the frequent rubbing of oil over all parts, but
especially on end grain, is equally beneficial if the throat has
been previously plugged and filled. Moreover, overhead plunging
is not always convenient.