Screw
Machining -- In 1873 Christopher Miner Spencer developed an
automatic lathe to manufacture screws in one operation. Today
it is used for rapid and accurate production of countless
varieties of duplicate parts from almost any material. The
operations that can be performed on automatic screw machines
are single-point turning, form turning, facing, chamfering,
boring, drilling, reaming, shaving, tapping, threading, counter-boring,
countersinking, knurling, milling, trepanning, roller burnishing,
broaching and cutoff.
In
1883, two mechanics, Edwin Henn and Reinhold Hakewessell shared
an interest in developing a multiple-spindle automatic lathe.
Their concept employed four spindles through which bars of
metal could be fed and made to revolve while cutting tools
were advanced to positions by cams. Henn and Hakewessell built
their pioneer four-spindle multiple in 1893 in a one-room
house with salvaged parts. The first successful four-spindle,
1" capacity machine was named ACME and the company was
organized to build it in 1896.
In
1928 the completely redesigned its line of automatics and
introduced a six-spindle model, and an eight-spindle version.
They were then able to offer a range of machine sizes that
would accommodate up to 8" diameter bars and a choice
of four, six or eight-spindle models.
The
multiple-spindle bar machine can perform side and end operations
on each spindle simultaneously. The first spindle position
feeds the bars of material out by an amount equal to the workpiece
length plus the width of the cutoff tool. The last spindle
position is the cutoff station. Independently operated attachments
may be added to allow the operator to broach, burnish, hob,
knurl, mill, slot, stencil, and thread.
Swiss
Screw Machining -- The sliding headstock automatic machine
was invented and built at Bienne in 1872 by Mr. Schweizer.
It was developed for the production of collets for watch balance
springs. A year later he added an attachment to the machine
for the production of watch screws. In German Schweizer means
Swiss, thus, the sliding headstock automatic became known
as the "Swiss-Type Automatic".
The
Swiss Automatics feature a sliding headstock, guide bushings
and cross tools. The headstock moves lengthwise on the dovetail
slide of the solid machine body. It gives the bar its rotation,
and performs an independent function: it feeds the bar past
the tools during the operation cycle. Cams control the longitudinal
movements with near mathematical precision, transferring accuracy
to the turned part. The guide bushing is located just behind
the cross tools and is in alignment with the headstock. It
cancels the effect of the pressure created by removal of material
from the bar and prevents it from bending. The bar is held
in two places--by the collet located in the headstock spindle
nose and by the guide bushing. The latter is adjustable and
can be set to eliminate play. The bar is presented to the
tools free from bending and chatter. Cross tools are cam controlled
and move only in a straight line to and from the center of
the bar. Cutting tools are arranged fanwise around the guide
bushing. By combining the radial movements of the cross tools
with the longitudinal movements of the headstock the contours
of the most intricate components can be generated. The use
of simple inexpensive and easy-to-grind single-point tools,
working very close to the guide bushing, offers an advantage.
It allows the highest possible precision in the reproduction
of contours, from the simplest to the most complex. The combination
of the sliding headstock with guide bushing and cross tools
makes it possible to obtain consistently excellent surface
finishes.
Many
turned parts are best suited to Swiss Automatics, such as
parts that can only be seen with magnification to very large
parts 32 mm/1.250" diameters up to 200 mm/8" of
turned length. The machine can handle a workpiece to 660 mm/26"
in overall length.
Escomatic
Wire Machining -- It is unlike other automatic screw machining
in that the material remains stationary and the tools rotate
around it. This allows machining material from coil stock
and eliminates bar material loading time. Also, one operator
can tend several machines.
The
spindle, supported in the headstock in ball bearings to ensure
concentricity and alignment, carries the rotating toolhead,
which is equipped with three tools. The tools are actuated
independently and are controlled by separate cams. They are
radially and axially adjustable.
The
stock is supported and passed through a stationary guide bushing
situated in the rotating toolhead. At the end of the feed
tube, between the nonrotating guide bushing and feed collet,
a holding collet is used to clamp the workpiece, eliminating
axial movement of the part during straightening of the stock.
Forward feeding of the stock is provided by a feed slide combined
with the feed tube and collet, all controlled by a simple
plate cam. Coil stock is straightened by means of a rotating
device, an integral part of the machine. Straightening of
the material is achieved by a combination of rotating jaws
moving axially.
Use
of a special holding collet next to the feed collet for forward
feeding of material, eliminates for opening, return movements
and clamping is necessary. This operation is performed at
the same time as the recess or cutoff operation. The counter
collet is located directly opposite the rotating toolhead.
It has an axial adjustment of up to 20mm/0.75". The counter
collet is set as close as possible to the tools and always
holds the workpiece firmly when forming or cutoff work is
done. This capability enables higher feed rates and burr-free
cutoff. Maximum capacity is 6.350 mm/1/4" diameter and
62 mm/2.44" in length.
Runs
of 1000 pieces or more make automatic screw machining an attractive
alternative. The range of materials usable on automatic screw
machines is broad. All grades of steel, copper alloys, brass,
aluminum, precious metals, hard rubber, machinable plastics,
phenolics and wood can be processed. Rounds, squares, hexagons,
round-cornered hexagons, tubing, rectangles, ellipses, cogged
or lobed shapes can be accomplished on automatic screw machines.
Cold-rolled stock is preferred, but hot-rolled materials can
be turned under certain conditions.
Machines
are available that can handle bars or tubes up to 8"
diameter. Most multiple-operation machining is done on bars
that range from 1/4" to 2" round. The standard bar
length is random 12 ft. but shorter lengths pose no special
problems. Tolerances of +/- 0.002" on length and +/-
0.001" in diameter are considered the norm in screw machining.
