Alpena weekly argus. [volume] (Alpena, Mich.) 1871-1893, 1884-02-06
How Screws Are Threaded.

screw tnlchuS are 'Orlglndtec' IN
the lathe usually. All lathe turning,
with regular ar-constant-feed of the
turning tool, is screw cutting, or
threading; the tool cuts a spiral around
n revolving cylinder.
1t is evident, therefore, that by in
crcasing the speed of the feed relative
to that of the revolving cylinder, and
having the point of the cutter properly
shaped, screw thread would result,
instead of pairing off of the entire sur
face of the cylinder. All important
actuating or working screws, as those
for feeding on machine tools, are
formed in this way, and large numbers,
also, of ordinary machine screws. which
when once seated are expected TO re-
main in SitH until the machine or inn
plement of which they form part is
worn out.
Wood screws, as screws for fastening
wood TO wood, metal to wood, etc, are
threaded in similar manner, the
thread being cut from the solid by a
single cutter removing the material
between the threads.
Large numbers of screws are thread
cd by dies, which may be called hollow
screws, or nuts with cutting edges.
These, by rotating, form the feed us
well as the cutting device for threading
the smooth cylindrical rod or bar
Some of these dies are worked by hand,
others by power, but in either case the
cut, by modern and improved dies, is
clean, and the thread is formed from
the solid. The old fashioned dies were
adjustable so as to be ''set up, and
could be made to cut several sizes OF
diameters. Much of their work was
done by pressure, or squeezing, and n
part of the thread was "rased" instead
of being cut from the solid material.
There are adjustable dies made now,
but they are so formed as to do solid
cutting.
There is another method of cutting
threads direct from the solid, and that
is by milling. The machine is entirely
automatic, the blank 10 be cut being
rotated as in lathe, and rotary mill
ing tool rotating against ii at an angle
adapted to the pitch of the thre ad de-
sired. As the blank revolves slowly to-
ward the cutter, the cutter revolving
more rapidly forms the thread by being
fed along over the blank rs is the cut
ting tool is lathe. The milling tool is
so formed in cross section ~ to produce
any shape of thread desired.
Threads on large cast iron screws
are sometimes formed simply by being
cast, and formerly there was much
cheap small work of that sort in the
market.
Threads may be raised by forging IN
dies, and some good work by this Is pro.
Ia hnvrnupy.
an after finish in the lathe is desirable,
For some peculiar purposes threads
%. '',-.ca - BY syiS.ing ...,:es;.,1r
flat bar; common form of hand drill
that has superseded the bow drill being
a case in point. The stock of this drill
is bar, square in cross section, twisted,
and which is rotated by sliding n
loosely fitting nut rapidly back and
forth over its length. A familiar in
stance of screw thread of this dcstrip-
ton is the ordinary augcr or bit, the
cross section of which is q nattencd
parallelogram like flat bar.
one peculiar method Of forming
screw threads remains TO be mentioned.
II i that of raising thread by rolling
between dies under pressure. There is
great deal of what is known as
"brght wire goods in the market,
which are threaded. In many cases
these threads are formed by simply roll
ing one revolution, or a little more -
the wire between two hardened steel
plates that are corrugated spirally to
form, when combined, a continuous
thread. Sufficient pressure is applied
during the rolling which, however, is
very rapid-to raise the metal from the
annealed wire enough TO make thread.
In this case the threaded portion is con-
sidcrably larger than the stock or wire,
at least half the depth of the thread on
each side.
The threads in nuts are produced eth
er by the originating" method, cutting
them in lathe, by being tapped, or
sometimes by being cast of soft metal,
as brass, on threaded core OF hard
metal, as iron or steel. But nuts are
mostly threaded by tapping, running
one, two, or three successive taps through
them either by hand or in power ma
chine. Nuts of very thin material. as
sheet brass for lamptops, jar covers, etc.,
are formed simply by rolling between
spirally corrugated rolls, n work anal
ogous to "bcading' on tin ware. Sci
entifc Amertcan.