AN IMPROVED METHOD OF AND MACHINE FOR CUTTING SCREW-THREADS
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by Otto Schober at the Office of the
Commissioners of Patents on the 18th May 1880.
OTTO SCHOBER, of Berlin, in the Kingdom of Prussia and Empire of Germany.
"AN IMPROVED METHOD OF AND MACHINE FOR CUTTING SCREW-THREADS."
My Invention relates to an improved method of and machinery or apparatus for
cutting screw-threads, which are produced by means of milling-cutters in such a
manner that several threads, adjacent to each other, are begun simultaneously;
they are consequently separated each from the other, and are combined in a
continuous screw-thread during one revolution of the object upon or in which the
threads are to be cut.
For this purpose I place the object or article to be screw-threaded either between
two centres or in a chuck, as in a lathe. I provide a milling cutter arranged to run
in the direction of the threads to be cut, that is to say, it is set in an oblique
position, so that its axis is directed rectangularly to the screw-line. . The surface
of the said cutter is cut in such a manner that there are several parallel rings
situated near each other, the section of which corresponds with that of the screw-
thread to be produced. These rings are crossed by several grooves or furrows, so
that cutting teeth are formed, the profile of which is the same as that of a thread-
chaser. In consequence of the above described position of the cutter axis to the
axis of the object or article, the profile of the cutter must be curved more or less.
The cutting of screw-threads according to my Invention is effected in the
following manner, that is to say:-
The revolving milling-cutter is brought near to the stationary-object or article on
which the threads are to be cut, and is placed rectangularly to the axis of the said
object, and the cutting of the threads begun by the teeth of the cutter, the cutting
being continued to the desired depth. By this operation as many parallel separate
threads are begun as the milling-cutter has parallel rings on its surface. After this
has been, effected, the said object is slowly turned, and the milling cutter is
simultaneously moved along parallel to the axis of the said object. By this
operation the threads commenced as above described are continued and combined
in a screw-thread during one revolution of the object, as the longitudinal movement
of the cutter is so timed that every one of the rings above described meets the
thread which was begun by the adjacent ring.

page_text: For cutting interior screw-threads in hollow cylinders, the milling cutter is
placed inside the latter, and the operation is the same as for cutting screw-threads
on an outer surface.
It is necessary that the axes of the milling cutters applied in various cases should
be brought into different oblique positions to the axes of the objects for producing
different pitches of screw-threads. For this purpose I may arrange the head-stock
with the milling-cutter-spindle on a horizontal bolt situated rectangularly to the
axis of the object to be cut, and the head-stock is so arranged that the milling
cutter will run whatever may be the position of its axis.