Improvements in Dies for Screwing Machines or Apparatus.
Year: 1897

page_text: Date of Application, 12th Jan., 1897-Accepted, 27th Feb., 1897
[Communicated from abroad by JOSEPH BERESFORD RENSHAW, of 202 High
Street, Hartford, Connecticut, United States of America, Engineer.]
Improvements in Dies for Screwing Machines or Apparatus.
I, ERNEST RICHARD ROYSTON of 15 Water Street, Liverpool, in the County
of Lancaster, C.E., Fel. Chart. Inst. P.A., 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 :-
This invention is an improvement relating to dies for cutting the external threads
of screws, and particularly to those dies which contain removable and adjustable
chasers. This improvement pertains to the chasers themselves and to the means
whereby they are clamped in their collet or holder, adapting them to be manufactured
more economically and in such a way as to avoid the distortions to which their
present usual form renders them peculiarly liable.
Figures 1, 2, 3, 4, 5, 14 and 15 represent various forms and methods of application
of my improvement, while Figures 6 to 13 inclusive represent the most approved
pre-existing form of chasers, and these latter are herein shown in order to illustrate
their defective and objectionable features so as to show by comparison the nature
and scope of my present invention.
Figure 1 of the drawings is an end view of a die of the class to which my invention
is especially applicable, showing four cutting chasers and their holding means, made
in accordance with my invention.
Figure 2 is a side view, partly in section taken on the center line of Figure 1,
showing an end view of one of my improved chasers with my improved means for
clamping it in its collet.
Figure 3 is a side view, and Figure 4 an end view, of one of my improved chasers
separate from its collet.
Figure 5 is a fragmentary end view corresponding to that of Figure 1, showing
my improvement as adapted to the cutting of left hand threads.
Figures 6 and 7 are sectional views corresponding in part to that of Figure 2,
showing the two different methods hitherto accepted as the best practice of
fastening chasers of the form shown in Figure 8 in position in their collet.
Figure 8 is a side view of a chaser made in accordance with the best accepted
previous practice.
Figure 9 is a sectional end view taken on the line 9-9 of Figure 8, showing the
character and direction of the distortion which most commonly results from the
process of hardening this form of chasers, while
Figures 10 and 11 are end views of the chaser of Figure 8, showing in a measure
the effect of distortion upon the teeth of the chaser.
.
Figure 12 is a diagrammatic view representing the flat development of a circle
corresponding to the dot and dash circle shown in Figure 1, showing the four
chasers of that figure side by side in their proper relation to each other, illustrating
how the teeth of a properly made chaser should conform to the geometrical lines
representing the angle of the spiral formed by the thread they are intended
to cut.
Figure 13 is a diagrammatic view similar to that of Figure 12, illustrating in

page_text: comparison therewith the effect of the distortion of the screw threads of four
chasers similar to that of Figures 9 and 10.
Figure 14 is an end view of a die having a square collet adapted in accordance
with my invention to receive my improved chasers and their holding means.
Figure 15 is a side view, partly in section on the line 15, of the die of Figure 14.
In this die the adjustment of the chasers to their cut is effected by means of
independent screws, instead of a ring.
In order to show clearly and fully the nature and scope of my invention, and its
relation to the prior art, is deemed necessary to set forth as briefly as possible the
state of this particular branch of that art, and the conditions thereof under which
arises the desirability and the importance of the present invention.
Figures 1 and 2 of the drawings represent a chaser die, which in the general
form herein shown is manufactured in very large quantities. The methods
employed in the manufacture of this die are calculated to make its parts perfectly
interchangeable, so that new chasers may at any time be ordered from the
manufacturers and inserted in a collet to replace those which have been worn out.
This is more difficult than would appear at first sight, for the reason that the
cutting teeth of each one of these chasers must not only agree in pitch with those
of the other chasers of its set, but each one must when placed in the collet have its
cutting teeth located in exact coincidence with the spiral described by the teeth of
the other chasers. The significance of this requirement will be better understood
by reference to Figure 12, which is a diagrammatic representation of a flat
development of the dot and dash circle shown in Figure 1, with the chasers
represented side by side. The thread teeth are represented upon the faces of these
chasers by lines which stand at a proper angle to the base line b-b upon which the
lower edges of the four chasers rest. The lines c, d, e represent the proper angle
of the spiral formed by these threads, corresponding to the path upon which the
succeeding teeth of the chasers must follow each other in the operation of cutting a
thread upon a bolt. In the view shown in Figure 12 the chasers are represented
as being free from distortion and, therefore, the lines upon their surfaces which
represent the thread teeth coincide exactly with the lines c, d, e, which represent
the angle of the spiral described by them when in their cutting position, shown in
Figure 1. From this diagram it will be seen that these dies in order to follow each
other properly around the thread of a bolt, must invariably occupy this exact
relation to one another. In order to secure perfect interchangeability it is
therefore necessary in the manufacture of these chasers, and of the collets for
holding them, that they shall be exact as to at least three particulars: first, that
they must be equally spaced circumferentially around the collet; second, that the
thread teeth on each chaser must be so located as to coincide with the imaginary
spiral lines describing the thread corresponding to the line c, d, e of Figure 12, and,
third, it is necessary that after the thread teeth have been cut upon the soft chasers
in this exact and proper relation to one another, that the chasers shall be hardened
in such a way as not to distort them, and thus throw the thread teeth out of their
proper relation to the spiral.
Furthermore, as a means of satisfying the second of the above enumerated
requirements, it is necessary that the teeth of each chaser shall be located thereon
in an exact and unvarying relation to that portion thereof which rests upon the
base line - corresponding to the bottom of the slots in the collet."
As a
convenient way of securing this exactness in the relation of the teeth, the chasers
are numbered 1, 2, 3, 4, as shown in Figure 1, and are regarded as four distinct
kinds, each of which has its teeth cut or "hobbed " in an unvarying relation to its
base or gauging edge. This enables the chasers of a certain number to be
interchanged with all others of the same number.
After having taken all possible care and pains in the manufacture of the chasers
shown in Figure 8, it is found that the hardening process is liable to distort them in
the way represented in Figures 6, 7, 9, 10 and 11. This distortion is due to the
presence of the groove 5 made to receive the point of a set screw which is employed

page_text: to press the chaser to its seat in the collet, as shown in Figures 6 and 7. That
groove, being cut across the side of the chaser so as to allow of adjusting.it in
the collet, so weakens the chaser as to make it peculiarly liable to bend along the
general line of the groove 5 during the hardening process, thus causing the
distortion of the cutting teeth above described. The curved sides of the distorted
chasers are then ground or lapped so as to enable them to be inserted in their
respective slots in the collets. But this trueing of the sides of the chasers does
not correct in the least degree the distortion of their teeth, which therefore do not
follow each other properly in cutting a thread, thereby producing imperfect
threads, and causing an undue amount of friction by the wedging action of the
teeth during the cutting operation. This also causes a waste of power, besides
wearing out the teeth of the chasers very rapidly.
A further objectionable feature of this method of fastening the chasers in the
collets is that the screws which enter the grooves of the chasers are very liable to
become loosened by the strains to which the chasers are subjected in working,
especially when their teeth do not "lead" correctly, or in other words, do not
exactly follow each other in true spirals, as above explained. On account of the
changes to which these screws are liable in hardening, it is necessary to make them
loose in the thread in order to have them interchange with certainty, and a screw
which is thus loosely fitted in its thread is poorly adapted to maintain a suitable
grip upon the chasers when applied as shown in Figures 6 and 7, especially when
the chaser is distorted in the direction shown in the latter figure, which allows it
to rock upon a point opposite to the point of application of the set screw.
A further objection to this manner of applying the screws arises from the
difficulty of making the end of the screw bear equally well on both sides of its
axis. For example, referring to Figure 6, if the screw should happen to bear
hardest against the upper side of the groove the effect would be to raise the chaser
away from its base, and it would also operate to roll the chaser end wise away from
its adjusting ring 9 when the screw is turned toward that direction to tighten it.
This feature is a constant source of annoyance in adjusting the chasers to the size
they are to cut, for in tightening the screw it is liable to throw the chaser away
from the ring, or other adjusting means. Then when the strain of the cut is
thrown upon it the chaser is forced back against the ring, turning and thus
loosening the screw, and at the same time increasing the cutting size of the die.
The same fault is found with the application of the screw shown in Figure 7,
inasmuch as it is equally difficult to make the end of that screw bear equally well
over its entire end surface, and whichever portion of that surface bears upon the
chaser, is liable by its wiping action to move the chaser and thus disturb the
adjustinent.
It is well-nigh impossible to make the screw of Figure 6 so that its bevelled
point shall be concentric with the axis of its threads; or the screw of Figure 8 so
that its flat end shall be at right angles with the thread axis, unless those screws
are both made upon lathe centres, which would be far too expensive a method for
commercial purposes. This well-known irregularity to which those screws are
peculiarly liable adds to the difficulty of making them bear properly upon their
chasers.
A further objection to the form of both the screws shown in Figures 6 and 7 is
that the metal which surrounds their slots is so reduced by the thread as to make
them very liable to be broken or split off by the use of the screw driver thereon,,
and the slotted end is so reduced in size as to require the use of a small screw
driver; thus reducing the amount of force that can be applied in tightening the
screws upon the chasers.
Having thus explained as briefly as possible the nature of the objections which
exist in practice to the present form of chasers, and to the present methods of
securing them in this class of die, I will now describe the features of my improved.
die, whereby these objections are obviated.
The collet 8 and its adjusting ring 9 may be, as shown, substantially like those

page_text: hitherto in use, my improvements relating more particularly to the chaser and to
the means employed in holding it to place. That chaser 10, as shown in detail in
Figures and 4, is made of uniform thickness, excepting at its upper side 14,
which is bevelled to agree with the body of the tapering screw 11. It is to be
,observed that the bevelled portion 14 of the chaser is adjacent to that part of its
thread which in the usual practice is cut away to enable the chaser to start
gradually upon its cut, so that even if the chaser could be distorted at this point
in hardening, as a result of the reduction of its cross sectional area, it will be seen
that that distortion would not in any way effect the "lead" of the chaser or the
agreement of its teeth with the lines c, d, e of the diagram Figure 12.
The form of the screw 11 and its relation to the chaser and to the collet is best
shown in Figures 2 and 15. The dies shown in Figures 1, 2, 14 and 15 are adapted
to cut right hand threads, turning in the direction of the arrow, and it will be
observed that the screws are located on the leading or advancing sides of these
chasers. It will also be observed in Figures 2 and 15, that the thread of the
screw 11 is made left banded. This is so made in order that the backward
crowding action of the work upon the chasers will tend to tighten rather than
loosen the screws because of the threads thereof being left handed. When used
in connection with a left hand cutting die, as shown in Figure 5, the screw should
be on the opposite side of the chaser 10, which in such a die, will be the leading
side, as indicated by the arrow, and in this case the thread of the screw 11 should,
of course, be right handed.
This method of applying the plain portion of the screw between the bevelled
side of the chaser and the adjacent tapering side of the hole in the collet,
interposes a solid metal-to-metal relation between the two surfaces without
imposing any appreciable strain upon the threads of the screw, excepting, that
slight tension necessary to draw the tapering portion of the screw solidly into
contact with the collet and the chaser. The solidity of the joint is thus independent
of the accuracy of fit or the strength of the thread itself, and as the strain of the
cut is not thrown upon the thread, it is not liable to become stripped or otherwise
damaged as in the old form. The nick of my improved screw is also less liable to
be injured by the application of the screw driver thereto, inasmuch as it is located
in an enlarged portion of the screw which is free from threads, thereby permitting
the use of a larger screw driver, and preventing the liability of splitting or
breaking off one side of the screw, which, as above explained, frequently happens
in the use of screws like those shown in Figures 6 and 7.
A further advantageous feature of this invention resides in the fact that the
face of the die may thereby be made smooth and free from unfilled recesses such,
for example, as that shown in Figure 7, for the screw 7.
It is not essential that the bevelled portion 14 shall extend entirely across the
upper side of the chaser 10, as shown in Figure 3, as it will sufficiently serve its
purpose if made wide enough to permit of the required adjustment of the chaser.
But I prefer to make it as shown in Figure 3, as the bevelled portion 14 may then
be readily finished off with the same milling cutter which finishes the adjacent side
of the chaser, and at the same operation. Therefore, these surfaces may be always
accurate in their relation to each other and to the teeth, whereas the groove 5 of
the chaser of Figures 8 and 9 must be made by an additional operation, involving
additional cost and the liability of variation in the position of the groove relative
to the screws 6 or 7; and that variation is liable to be increased by the subsequent
distortion due to the hardening of the grooved form of chaser, as hereinbefore set
forth.
The chasers shown in the die of Figures 1 and 2 are simultaneously adjusted to
their cutting position by means of the adjustable ring 9, which is screwed upon the
collet, and has an inner bevelled annular portion fitting against the correspondingly
bevelled rearward ends of all the chasers. This arrangement is best shown in the
sectioned portion of Figure 2.
This construction is, however, available only in the case of a cylindrical collet,

page_text: and I have devised an improved method of adjusting and clamping my improved
chasers when used in connection with a collet of polygonal form. These are
sometimes used with polygonal holding or driving chucks, being usually of
the four sided or square form shown in Figures 14 and 15, it being obvious,
however, that this improvement may be used in connection with a collet having
any number of sides or chasers. This improvement dispenses with the annular
ring 9, and consists in providing a screw 16 adjacent to, and parallel with, each of
the chasers to be adjusted. This screw is threaded in the collet, and is provided
with an enlarged head bearing against the rearward end of the chaser, so that by
turning the screw forward the chaser is forced toward the centre of the die. The
clamping screws 11 are similar to those shown in Figures 1 and 2, and operate in
a similar manner. The adjusting screws 16, and the clamping screws 11, are
preferably arranged on opposite sides of their respective chasers, as shown in
Figures 14 and 15. By the use of these independent adjusting screws it will be
seen that the cutting teeth of all of the chasers of a die may be brought into exact
concentricity with the axis of rotation of the spindle on which the die carrying
chuck is mounted, in case the holding jaws of that chuck may be more or less
eccentric therewith.
Having thus particularly described and ascertained the nature of this, my said
invention, and in what manner the same is to be performed, I declare that what
I claim is :-
1. As a new article of manufacture, a radially cutting die chaser, having a
relatively narrow bevelled surface adjacent to one edge of its leading side face, for
the purpose specified.
2. In combination with a radially slotted collet or holder therefor, a die chaser
having a relatively narrow bevelled surface adjacent to one edge of its leading side
face, with correspondingly bevelled clamping means engaging therewith.
3. In a die of the class specified, in combination with a radially arranged chaser
die, a screw located upon the leading side of the chaser with its axis parallel with
the axis of the die, the screw having a plain tapering portion for engaging with a
correspondingly bevelled portion of its chaser, and having a threaded portion
whereby the plain portion may be tightened upon the chaser.
4. In a die of the class specified, in combination with a chaser thereof, a screw
located upon the leading side of the chaser with its axis substantially parallel with
the axis of the die, having a plain tapering portion adapted to bear against a
correspondingly bevelled portion of the chaser, and having a threaded portion by
means of which it may be adjusted endwise, the threaded portion being left handed
when employed in a right hand die, and being right handed when employed in a
left band die, substantially as described and for the purpose specified.
5. In a polygonal chaser holder or collet, means for adjusting each of the
chasers to their cutting positions, consisting of a screw located substantially
parallel with the chaser and having a head engaging with the rearward end
thereof, so as to carry radially toward the work, with clamping means, consisting
of a screw located upon the opposite side of the chaser and parallel therewith, and
having a bevelled head adapted to bear against a correspondingly bevelled portion
of the chaser, substantially as described.
Dated this 11th dow of January 1807
CHEESBROUGH & ROYSTON,
15 Water Street, Liverpool, Applicant's Patent Agents.