An Improved Apparatus for Simplifying the Cutting of Screw Threads.
Year: 1894

page_text: Date of Application, 3rd Apr., 1894-Accepted, 13th Oct., 1894
COMPLETE SPECIFICATION.
An Improved Apparatus for Simplifying the Cutting of Screw
Threads.
I FRANZ BRAUN of No. 12 Ziegelstrasse Zerbst in the German Empire, Manu-
facturer of Machine Tools and Iron Founder, 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 subject of this invention is a device adapted to be attached to screw cutting
lathes fitted with leading screws or spindles, its object being very materially to
facilitate and simplify the cutting of screws having an odd number of threads per
inch, or such as have only,, or 16 of a convolution for every inch.
A serious inconvenience which the performance of work of this class has been
attended with hitherto, is, that the operator, in addition to moving backwards the
slide rest by means of the crank provided for the purpose, and to adjusting the tool,
or cutter, was obliged to regulate the pitch of the screw which was being cut,
either by counting the number of revolutions of the leading screw or by making
chalk marks upon the leading screw and the cam, so as precisely to regulate the
point, or position of the leading screw, at which the split "locking" nut should be
thrown into gear with the leading screw.
In cutting steep pitched screws, where the leading screw has to revolve at a very
great speed, comparatively speaking, and also in the case of screw threads having
tore pitch, the method just described is wholly inapplicable, it being necessary
in those cases for the slide rest or support to be allowed to run back in operation :
and this result is attained by causing the spindle of the lathe to turn to the right,
so that, especially in the case of long screws, considerable loss of time is
experienced.
These drawbacks are entirely removed by the improved lathe attachment herein
described, and the essential feature of which is, that an index device, having a
graduating circle or dial, is combined directly with the leading screw, whereby all
positions are indicated at which the lock-nut should be thrown into gear.
In the accompanying drawings illustrating our improved lathe-attachment,
Figure 1 is a vertical section and
Figure 2 a plan thereof, showing it detached, while
Figures 3 and 4 are respectively a side and a front elevation, showing the
improved device in position on the lathe.
The construction of the device is as follows:-Upon a vertical spindle w, at the
lower end thereof, there is mounted a screw or worm wheel A. which receives rotary
motion direct from the leading screw. This spindle w, is firmly supported by the
block or bracket b secured to the slide rest, and has a toothed wheel B at its upper
end, which wheel is in gear with a similar wheel C which imparts motion to a
This spindle c
spindle supported in a boss provided in the block or bracket b.
carries an index hand D at its upper end. Over the two toothed wheels there is
arranged a protecting hood or guard E graduated on its upper surface by strokes
extending in a radial direction to the axis of the index spindle and corresponding
to the various pitches of screws which it may be desirable to cut, so that the lock-
nut (Figures 3 and 4) may always be safely thrown into gear when the axial line
of the index coincides with any given division line on the corresponding circle.
Before starting the screw cutting operation, the index D should be so adjusted
that, after the tool and "lock" have been thrown into gear or as above set forth, the
split nut brought into engagement with the leading screw, the index D, which is
provided with an elongated aperture, is displaced to a sufficient extent for the index

page_text: point to meet the circle corresponding to the pitch of the screw thread to be cut,
and to coincide with a given division line thereof; after which the index may be
tightened upon the spindle c by means of the nut e.
For the better comprehension of what follows, it should be remembered that what
is here understood by "pitch" is the number of threads or convolutions per inch.
It is well known that a leading screw of n pitch must complete n times as many
revolutions as there are units in the denominator m of the fraction indicating the
pitch of the screw-thread to be cut; and not until this number of revolutions has
been accomplished, can the "lock" be thrown into gear. If these revolutions be
expressed by V then
V = D. m.
Supposing for example that the pitch of the screw to be cut is 216; then the
gearing of the lock, in a lathe the leading screw of which has three convolutions
per inch, should not take place until the leading screw has completed n. m = ▼
or 3.6 = 48 revolutions.
To determine the relation between the leading screw and the point of the index,
a number should be taken which is divisible by the various numbers of revolutions v
to be completed by the leading screw for the different pitches of screws, or in other
words the smallest common multiple of v. Thus in a case of lathes in which the
leading screw has two three or four threads per inch the proper or preferable
relations between the leading screw and index mechanism would be, respectively,
1; 64, 1; 96, 1; 128.
The reciprocal value of this ratio divided by the values of v, will give the number
of parts into which the circles corresponding to the different pitches should be
divided. Thus, if u be the reciprocal value of this ratio or the smallest common
multiple of v, and t the number of divisions or graduations in the circle, then-
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MARKS & CLERK,
18, Southampton Buildings, London, W.C., Agents.
MARKS & CLERK,
18, Southampton Buildings, London, W.C., Agents.