_SHAPING MACHINES._
Shaping machines as machine tools occupy a middle place between
planing and slotting machines; their movements correspond more to
those of slotting machines, while the operation of the tools is the
same as in planing. Some of the advantages of shaping over planing
machines for certain kinds of work are, because of the greater
facilities afforded for presenting and holding small pieces, or
those of irregular shape; the supports or tables having both
vertical and horizontal faces to which pieces may be fastened, and
the convenience of the mechanism for adjusting and feeding tools.
Shaping machines are generally provided with adjustable vices,
devices for planing circular forms, and other details which cannot
be so conveniently employed with planing machines. Another feature
of shaping machines is a positive range of the cutting stroke
produced by crank motion, which permits tools to be stopped with
precision at any point; this admits of planing slots, keyways, and
such work as cannot well be performed upon common planing machines.
Shaping machines are divided into two classes, one modification
with a lateral feed of the tools and cutter bar, technically called
"travelling head machines," the other class with a feed motion of
the table which supports the work, called table-feeding machines.
The first modification is adapted for long pieces to be planed
transversely, such as toothed racks, connecting rods, and similar
work; the second class to shorter pieces where much hand adjustment
is required.
An interesting study in connection with modern shaping machines is
the principle of various devices called 'quick return' movements.
Such devices consist of various modifications of slotted levers,
and what is known as Whitworth's quick return motion.
The intricacy of the subject renders it a difficult one to deal
with except by the aid of diagrams, and as such mechanism may
be inspected in almost any machine fitting shop, attention is
called to the subject as one of the best that can be chosen for
demonstration by diagrams. Problems of these variable speed
movements are not only of great interest, but have a practical
importance not found in many better known problems which take up
time uselessly and have no application in a practical way.
The remarks, given in a former place, relating to tools for
turning, apply to those for planing as well, except that in planing
tools greater rigidity and strength are required.
(1.) Why are shaping machines better adapted than planing
machines for planing slots, key-ways, and so on?--(2.) What
objects are gained by a quick return motion of the cutter bar of
shaping machines?