cut, and is this because they are overloaded? Not at all. Figure up at
even fifty pounds to the square inch of wearing surface what any
planer ought to carry, and you will find that it is not from
overloading. Twist the bed upon the floor (and any of them will twist
as easy as two basswood boards), and your table will rest the hardest
on two corners. Strap, or bolt, or wedge a casting upon the table, or
tighten up a piece between a pair of centers eight or ten inches above
the table, and bend the table to an extent only equal to the thickness
of the film of oil between the surface of the ways, and the large
wearing surface is reduced to two wearing points. In designing it
should always be kept in mind, or, in fact, it is found many times to
be the correct thing to do, to consider the piece as a stiff spring,
and the stiffer the better. The tooth of a gear wheel is a cast iron
spring, and if only treated as would be a spring, many less would be
broken. A point in evidence:

The pinions in a train of rolls, which compel the two or more rolls to
travel in unison, are necessarily about as small at the pitch line as
the rolls themselves; they are subject to considerable strain and a
terrible hammering by back lash, and break discouragingly frequent, or
do when made of cast iron, if not of very coarse pitch, that is, with
very few teeth--eleven or twelve sometimes.

In a certain case it became desirable to increase the number of teeth,
when it was found that the breakages occurred about as the square root
of their number. When the form was changed by cutting out at the root
in this form (Fig. 2), the breakage ceased.

a, Fig. 2, shows an ordinary gear tooth, and b the form as
changed; c and d show the two forms of the same width, but