06-10-2016, 12:34 PM
1458023925-3003JigBoringPrinciples.pdf (Size: 36.53 KB / Downloads: 18)
USED to its full extent with
accessory equipment, the
lathe is undoubtedly the
most versatile of machine tools,
and all types with rotating spindles
owe something to it. Certainly
each may perform some particular
operation or group of operations
faster and with greater facility
than the lathe,. as is the case with
bench and pillar drills, milling
machines, and universal and surface
grinders. Various operations special
to these machines can be performed
reasonably efficiently on
the lathe, given time, moderate
dimensions in the work and some
ingenuity in the set-up.
The same is true to a considerable
extent of the jig-borer, which operates
in the reverse way to a lathe, working
with a single-point boring tool-and
with special emphasis on accuracy.
For a normal boring operation on a lathe, the work revolves mounted in
the chuck or on the faceplate, and the
single-point boring tool is set to cut
and feed. For the corresponding operation on a jig-borer, the work is
stationary on the machine table,
while the single-point boring tool
revolves and is fed,
The reason for this reversal is the
nature of the work. In the main a jig
consists of a built-up plate or cast
box structure in which components
can be placed, for drills, reamers, etc.,
to be applied to them through accurately
positioned bushed holesthus
speeding production by obviating
marking off and numerous different
settings for each component. In
constructing the jig, all holes (some
T of them perhaps not very large) must
be accurately placed and boredand
it is easier to do this spinning a
boring tool than swinging a massive
casting or a long piece of plate
material.
1 The table of the jig-borer can be moved by accurate feed screws in two
directions at right angles; and having
picked up the position of a hole on
the feed screw micrometer collars,
the positions of others can be obtained from appropriate readings-or by
using end gauges against stops. On
a lathe, however, it would mean
loosening and resetting the work, a
longer and more difficult job. The
boring tool of the jig-borer must be
adjustable for sizing holes, and this
arrives from a form of radial feed to
the tool or its tip. Turning now to the lathe, the jigboring
principle is obtained, as at A,
with a boring tool in the independent chuck and the work mounted on the
vertical slide,, set to face the chuck
and fixed, hke the crossilide, by
tightening the gib-piece screws. Without
a special tool or holder, tool feed
can be given by manipulating the
chuck jaws, and testing results with a
gauge or callipers in the bore. Positions
of different holes can be obtained
from cross-slide and vertical slide
screws when these have micrometer
collars. Slides may have to be loosened
for moving; and while accuracy may
not compare with a jig-borer, it
should be equal to that from ordinary
marking off.
Ordinary cutting feed follows from traversing the saddle; and using a
tool of reverse shape, a boss can be
machined if required, as at B. Hole
centres in plate material or castings
may be located by marking off in the
ordinary way; then the scribed lines
can be set vertically and laterally to
a needle point spinning truly in the
chuck, as at C-the same as on a jigborer-and
noting the feedscrew readings.
For the lathe setting, a needle
can be soldered into a piece of brass rod. Having obtained the position of one hole (top left), the centre of
another (bottom right) follows from
a lateral feed X and a vertical feed Y.
Holes may be centre drilled, drilled,
then bored from the chuck.
On a jig-borer, holes at right angles
and other angles require the work to
be mounted on fixed and adjustable
angle plates. This principle may
follow on the lathe, though some
settings can be obtamed by turning
the slide, as at D, much easier than
by the normal lathe principle. Radius
machining, too, may sometimes be
simpler as at E, on a saddle casting, if large.