An Improved Method of Manufacturing Rack and Pinion Gear.
Year: 1893

page_text: te of Application, 5th June, 1893-Accepted, 8th July, 1893
COMPLETE SPECIFICATION.
An Improved Method of Manufacturing Rack and Pinion Gear.
I, GEORG ROHRMANN, of Mühlen Strasse 15 Lerbach, near Osterode a/ Harz,
in the Empire of Germany, Mechanician, do hereby declare the nature of this
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement :-
The previously used method of making rack and pinion gear on a small scale for
use in the manufacture of watches, scientific instruments and like purposes where
mathematically exact mechanism is required consists in cutting out the spaces
between the teeth of each of these parts by means of a pair or set of relatively
shaped cutters. This process however has, the disadvantage, that the accuracy of
the gearing materially depends on the greater or less degree of accuracy in the
matching of the cutters.
The present invention provides a method by which racks and pinions may be
made which fit to one another with an absolute and mathematical accuracy which
is practically independent of the skill of the workman, the cost of production of
this improved gearing being substantially lessened.
The racks and pinions, when made according to this improved method, are
particularly useful and suitable in the manufacture of any scientific instrument in
which exactness of acting is indispensable.
In the annexed drawing
Fig. 1 represents in side view a cutter applied to the cutting of a pinion.
Fig. 2 shows the same in plan.
Fig. 3 shows in side view a piece of work prepared for making racks.
Fig. 4 the same in plan.
Fig? a finished rack in elevation and plan.
The principle upon which this improved method is based rests upon the known
fact, that a worm and worm-wheel gear and a rack and pinion gear bear a certain
likeness to each other as the form of the flanks of the teeth may in either gear be
supposed to be described in the same manner. Thus if the cutter teeth in Figs. 1
and 2 are arranged in a helical curve of large diameter and slight pitch, in the
nature of a screw thread, and this cutter A of Fig. 2 and the body B in Fig. 4 are
provided with exactly equal and similar threads the threaded body B of Fig. 4
could be put in the place of the cutter A. (Fig. 2) and set in rotation, and would
form, together with the small pinion D shown in Figs. 1 and 2, a properly acting
worm and pinion gearing. The gearing can be considered as mathematically exact
owing to the exact similarity of the thread on the body B with the actual thread
of the cutter A. by which the spaces between teeth of the pinion have been cut.
If now a strip, such as indicated at a in Figs. 3 and 4, is cut out of the cylinder B
parallel to its axis it is obvious that this strip, which already represents a finished
rack, must with a mathematical exactness mesh with the pinion D.
In carrying this invention into practice two cylinders of equal diameter are
made, the one A (Fig. 2) of good tool steel and the other B (Fig. 4) of the
material of which the racks are to be made. These then suitably dressed and
polished on the turning-lathe are provided with an exactly similar screw thread
as illustrated in the drawing.
To obtain exactly the same thread on both bodies, both may be mounted
together on the lathe, the one behind the other, so that they form one continuous
cylinder the screw thread being then cut continuously over both bodies without
interruption.
This done, the steel body A is provided with properly shaped longitudinal slits
to convert the thread into a series of cutting teeth as in Figs. 1 and 2 and is then

page_text: ready for cutting pinion such as D, the teeth of which are slightly inclined toward
the axis.
The body B. is cut longitudinally into strips of convenient width and forms so
many racks accurately meshing with the pinion D.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
I claim is:-
An improved method of manufacturing mathematically exact rack and pinion
gear consisting in providing a hollow-cylinder B with a helical thread exactly
equal and similar to the thread of the helically arranged teeth of the cutter for
producing the pinion and subsequently dividing the said hollow cylinder into
longitudinal strips constituting racks substantially as described.
Dated this 5th day of June 1893.
R. HADDAN,
Herbert Haddan & Co.,
18, Buckingham Street, Strand, London, Agent for Applicant.