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THE INTERNATIONAL EXHIBITION, i876.
pulley-shaft. At each change of motion the pawl is thrown into gear by friction,
keeping up a positive motion of the crank-disk by the ratchet-wheel until
the pawl
is disengaged from its teeth by a positive stop.
Messrs. Sellers' method of lifting the tool-point on back motion in this
machine merits attention as another improvement on the usual plan, which,
in
most planing-machines consists in hanging the cutting-tool in what is called
an apron, so adjusted as to allow it to swing loose on the back stroke, but
to
be held rigidly when cutting. This arrangement is very objectionable in all
fine
planing, and especially in large planers where the tool is quite heavy. Various
ideas have been put into practice for actually lifting the tool-point clear
of the
work on the back stroke and dropping it into place again ready for action
on
the return, but the method here shown possesses especial ingenuity, lifting
the
tool in every position of the slide-rest, and doing so from within the cross-head
without interfering in any way with the automatic feed motion, the machinery
for working the feeds occupying the centre about which the adjustable part
of
the saddle rotates. This lifting apparatus is operated by a cord attached
to a
grooved segment which is connected with the crank-plate of the feed motion
by a link, a reciprocating motion being imparted to the cord corresponding
with
the motions of the table, and occurring only at the end of each table movement,
beginning with the reversion of each stroke. The cord is guided over sheaves
at
the ends of the cross-head and passes around a cord-wheel in the saddle,
having
at its other end a weight to keep it in tension. The' cord-wheel, by means
of a
pinion at the other end of its shaft, operates on a light annular plate-wheel
recessed into the saddle, around the central part containing the small feed
bevels.
In a spiral groove on the face of this plate-wheel slides a block which is
attached
to the end of a pipe surrounding the vertical feed-screw, and extending upward
through the casting, with a pair of elastic clamps at its upper end. These
clamps
operate by friction on a flat rod which passes the whole length of the vertical
slide
on its side next to the saddle, and has at its lower end, which is thickened
up, a
hole. The long arm of a bell-crank lever fits loosely into this hole, and
the short
arm extends down directly behind the tool-apron. The action of the cord imparts
motion to this bell-crank and affects the tool apron, pushing it forward
and letting
it fall back again into place as required. The action is perfect and beautiful,
with-
out interference with any of the functions of the machine in the least. When
the
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