Improvements in Screw Threading Tools.
Year: 1899

page_text: Date of Application, 5th Sept., 1899-Accepted, 23rd Dec., 1899
COMPLETE SPECIFICATION.
Improvements in Screw Threading Tools.
I, HERMAN DOCK, of 904, North Broad Street, Philadelphia, Pennsylvania,
Mechanical Engineer, do hereby declare the nature of my said invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement ;-
This invention relates to cutting tools, and means for actuating the same for
threading screws in engine lathes, my invention having for its object to cut
screw threads of superior accuracy with greater celerity, my improved tool in prac
tice being very durable and retaining its cutting edge in working condition for
the maximum time.
Screw threads are now commonly cut in engine lathes, by a tool having one
cutting point, said tool being adjusted after each cut to enable it at its next
operation to make a deeper cut.
In this way the tool besides becoming unduly heated is so dulled by reason of
making these repeated cuts that when the final or finishing cut is to be made the
cut at which the tool should be sharpest to do the best work is dull, and as a result
the final cut is not a smooth cut as it should be.
By the use of the single tool adjusted to make its series of cuts, it is very
difficult if not impossible to secure the proper perfection of form and accuracy
of pitch of the threads, for when the final or finishing cut is to be made, the
cutting edge of the tool is in its worst condition; rather than its best condition as
it should be for the final cut.
To remove a tool of this usual class, and sharpen it, necessitates from the
unavoidable change of its dimensions, a new adjustment, or to apply another tool
and adjust it involves very considerable delay, during which time the change of
temperature in the material being screw threaded makes an appreciable change
in the length of the screw, and in long screws, such as are required for the leading
screws of engine lathes, this change is very perceptable, and in precise machines
it is fatal.
The continued use of the same cutting edge of a tool throughout the entire
operation of making a long screw is only, if at all, practicable at such low veloci
ties of work as to be unremunerative, and even then the best perfection as to
accuracy of the thread is not attained..
To obviate these difficulties I have provided a tool shown as a disk having
extended therefrom a series of cutters, and preferably formed integrally there-
with (but they may be made separately from the disk and firmly inserted or
attached thereto) one cutter for each cut to be made in the production of the com-
pleted screw thread, said cutters being of progressively different lengths and
arranged in series, each cutter of the series when brought into operation effecting
a slightly deeper cut, the work of cutting the thread being thus apportioned to
the series of cutters so that the cutters are not overheated or unduly dulled, and
so that undue stresses on the material or work are avoided.
The disk and cutters constitute a tool, and by making the cutters integral with,
or rigidly attached to the disk, the cutters being defined or outlined clearly for

page_text: the work intended, they may always be made to occupy the same relative positions,
and they may be ground when dulled without changing the relations of the several
cutters of the series, one with relation to the other, or in relation to their points
of support when in action.
My improved tool is mounted rotatably on a pivot having combined with it
suitable means to impart to the pivot and tool, a defined to-and-fro, and to the
tool, a rotative movement with relation to the work, between each cut made in
the production of the screw thread.
While the tool is in operation the heel of the cutter is supported firmly on a
rest, and the tool is securely locked in place by means of a locking device.
The rest without any intermediate change of adjustment co-operates in succes-
sion with each cutter. Each cutter standing one after the other upon it in the
series of notches in the disk between the cutters, the sides of said notches consti-
tuting, one side a heel or supporting face for one cutter and the other side the
cutting face of an adjacent cutter, the dimensions from the acting face of each
cutter to its heel being uniform throughout the series.
A cutter having completed one of the series of cuts to be made in the produc-
tion of the screw thread, the tool is moved away from the work, it during such
movement retiring from the rest, and as the tool is again returned toward the
work, for another cut, said tool is rotated sufficiently to bring another cutter into
proper cutting plane, and this partial rotation having been effected, the notched
part of the cutter, in the final movement of the tool toward the work, is again
made to engage the rest referred to, which operates as a stop, so that when the
cutter fully arrives in correct position for cutting, its heel is brought against the
rest, and the cutter is firmly locked in place and it remains locked throughout the
operation of the cutter.
The accuracy of the screw thread made by my invention is secured by and
wholly dependent upon the operation of the tool irrespective of the skill of the
workman, each cut of different depth is made by a separate cutter, and faulty
work, due to inaccurate adjustment of a cutter by a careless workman, is
impossible.
The series of cutters of my improved tool are as stated of different lengths and
the peripheral edge of each cutter of the series is of uniform width from the acting
edge of the cutter to its heel, but for producing V shaped threads the width of
the several cutters at their peripheral edges varies throughout the series, the
peripheral edge of the last cutter to act being very much narrower than the
peripheral edge of the first cutter to act in the production of the completed screw
thread.
The following is a sufficiently full, clear and exact specification to enable otliers
skilled in the art to make and use the same, reference being had to the accom-
panying drawing and reference letters and ordinals marked thereon, in which,
Figure 1 is a plan view of my novel tool applied to work in an engine lathe, the
drawing showing parts of the lathe immediately supporting the tool and the
work.
Fig. 2 is a front elevation of the tool;
Fig. 3 is a right side elevation thereof;
Fig. 4 is a left side elevation thereof;
Fig. 5 is a section in a plane indicated by the line X X in Figs. 1 and 4,
looking in the direction of the arrows;
Fig. 6 is a section in the plane indicated by the line Y Y, in Figs. 3 and 4;
Fig. 7 is a section in the plane indicated by the line ZZ in Figs. 1, 3 and 4;
Fig. S is a detached side view of the tool;
Fig. 9 shows the tool in edge view.
Fig. 10 and 11 are top views of modified forms of cutting tool with duplex
and triplex cutters;
Figs. 12 and 13 respectively, are enlarged views of the cutters shown in Figs. 10
and 11

page_text: Figs. 14 and 15 show a modified form of the parts for retracting and advancing
the pivot and tool from and towards the work;
Figs. 16 and 17 show modifications of the pawl for rotating the tool;
Figs. 18 and 19 respectively, show the tool stock separately in the left side
view and in transverse section in the plane indicated by the line XX in Figs. 1
and 11;
Figs. 20 and 21, respectively, show in section and side view the bearings of the
pivot or bolt;
Figs. 22 and 23, respectively, show on top and side view the arbor and lever.
for locking the tool in engagement with the work;
Fig. 24 shows separately the bolt for pivotally supporting the tool;
Fig. 25 shows separately the pawl for turning the tool and a section of the
bearing supporting it;
Fig. 26 shows a projection of the screw cutting faces for producing V shaped
threads, and Figure 31 a like projection for producing square threads:
Figs. 27 and 28 respectively show in elevation and section the washer for hold-
ing the lever handle in position on its pivotal bolt;
Figs. 29 and 30 respectively show in front and end view the rest for supporting
the cutters.
Referring to the drawing, Figs. 1 to 5, a represents the head stock centre of an
engine lathe, the tail stock centre, the face plate, d the carrier transmitting
rotary motion to a cylindric bar e held between the centres and to be screw.
threaded; the tool post f is supported and may be moved by usual gearing con-
nected with the arbor of the lathe. The tool post f receives the stock y used to
support the novel tool to be hereinafter described:
-
L
The stock sustained in the tool post is provided with a guideway and with a
slot m, (see Fig. 18)
The guideway receives a movable bearing or slide shown separately in
Figs. 20 and 21, which slides in the guideway shown in Figs. 18 and 19.
This bearing or slide receives and supports a bolt or pivot h. having a heads,
the bolt receiving upon it the tool fitted rotatably thereon, said bolt being
extended through the bearing or slide and the slot m, and taking its scat in a
lever i The lever i has a stud at one end beyond the bolt, which pivotally
fits a link n, said link being pivotally connected at its other end with the rocker-,
arm o, suitably secured to a rock shaft having its bearing in the stock g, said
rock shaft having at its opposite end an attached dog q, (see Fig. 7 in section and.
in Figures 22 and 23); the dog, when said lever and rocker arm o are in the
position shown in Figs. 1, 3, 4, and 5, bears against the rear surface 2 of the bear-
ing or slide j, said dog at such time constituting a locking device holding the
bearing or slide in its extreme forward position with one of the cutters of the
tool in operative condition with relation to the work.
The stock has a projecting pin 1 (shown in Figures 1, 2 and 18)
against which the front, edge of the lower short arm of the lever i
contacts and acts as a fulcrum to the lever i, so that when the upper end of the
lever is pressed backwardly from the work it slides the bolt hand cutter away
from the work and at the same time the pivot draws the link and rock arm o
forward raising the dog clear of the rear end of the slide j, permitting the
slide to retreat, and the cutter z to retreat from engagement with the work.
The reversed motion of the lever i pushes the bolt, slide j and the cutter
toward the work and turns the dog into position to abut solidly against the back
end 2 of the slide holding the slide firmly in position for engagement of the.
cutter in the work. During the motion of the lever i slide and cutter just
described, the cutter z is turned upon the bolt by a pawl as hereinafter described.
and when turned so presents another cutting point for operation; the heel of the
cutting point is rested upon a support as hereinafter described.
The bolt h, (see Fig. 24) is threaded to receive a nutt said bolt being splined
at u to receive a feather, extended from the bearing or slide.

page_text: .
Between the nut and the lever i the bolt has applied to it a washer, having
a feather w, to also enter the spline u, such construction preventing the bolt and nut
from turning with the lever i.
The stock y in the bottom of the guideway k, is recessed in the part marked 3
(see Figs. 18 and 19) to receive the forked end of the rest 16 (shown separately
in Figs. 29 and 30) upon which slides the heel of the cutter as the tool is put into
its operative position, said rest preventing any rotation whatever of the tool while
operating. The stock has a set screw 45 to act on the said rest, to thereby cor-
rectly adjust the position and support of the rest to receive the heel of each ter
of the tool, (to be described) the said rest when once adjusted acting uniformly
to maintain the tool in any of its operative positions.
As shown in the modified form in Fig. 14, the bolt h is formed with an eccentric y,
and turns with a lever i, and fits and turns in a circular bearing formed in the
stock g, the eccentric acting to move and hold the bolt in its moving and in fixed
positions.
The tool z carried by the bolt h, (see Figs. 8 & 9) has its peripheral edge beveled
to present in cross section the profile of the intended thread space, and said edge
is cut or notched at 46 to leave a series of integral projecting cutters or teeth 4, 5,
6, 7, 8, 9, 10, 11, 12, and 13 with the spaces between.
The acting faces of each of these cutters is marked 14 each face being radial or
approximately so with relation to the disk said faces in connection with the profile
surface referred to presenting the suitable or desired cutting angles or edges.
Each notch or space 56 presents at one side thereof a surface 15, all of said
surfaces being equi-distant from the surfaces 14, the surfaces 15 constituting
heels which bear upon and co-operate with the rest 16 to retain the tool fixedly in
position when each of the several cutters is acting to do its work to cut its groove
in the work.
As the distance from the acting face to the heel of each cutter is uniform, and
the heels stand all in the same angle, a single adjustment of the rest 16 serves
for all the cutters. The several cutters of the series marked 4 to 13, are made suc-
cessively of different radial lengths so that each of said cutters to come into
operation may make a deeper cut than the one preceding it, but in some cases the
difference in the depth of this cut may be less between the two last cutters to
operate, than between the first cutter to operate and the cutter following it.
Whn the cutters vary slightly in length and each cutter forms a defined cut in
the production of the interspace of the screw thread, the cutters, the lathe and the
material being operated upon are never subjected to such stresses or strains as
to spring or twist the work aside, and thus impair the pitch of the screw to be
made.
By making the last cutter to act, of but slightly greater length than the pre-
ceeding cutter, a superior accuracy of finish of the final cut may be insured both as
to dimensions and smoothness of the surface, for the less the material removed
in the cut, the smoother the surface which will be left.
Each cutter has a peripheral edge extending from the acting face of the cutter
to its heel, and said face for the best results is uniform in width from
the acting face to the heel, but the peripheral portions of these several cutters
to produce V shaped threads vary in width one after the other (see Fig. 26) it
being understood that each cutter is to cut into the work a little deeper, than
the one preceeding it, each successive cut shaping and defining more definitely
the bottom of the screw thread to be made; for producing square threads the forms
shown in Figure 31 are used.
The lever i has a pawl 18 attached thereto, which engages the notches 46
between the series of cutters described.
As the lever is moved in the direction to withdraw the bearing or slide, the
bolt, and the tool from the work, the spaces 56 are retracted and disengaged from
the rest 16, and at the same time the pawl 18 carried by the lever i enters a new
notch or space in the periphery of the tool, so that thereafter as the lever i is

page_text: again moved in the opposite direction, the pawl 18 is in engagement with the
acting face of a cutter and, during the first part of the movement of the lever,
the pawl 18 acts on the face of the cutter to rotate the cutter the space of one
tooth about the bolt h, and thereafter, the rotation having been effected, the lever i
in its further movement effects a longitudinal movement of the bearing or slide j
in the guideway k, of the stock g, and causes the heel 14 of the cutter next to
operate to contact with the rest 16 and slide on to the rest and sufficiently beyond
it so that the profile of the cutting edge of the cutter stands beyond the rest 16,
in position to act upon and do its portion of the work in the production of the
screw thread. As the lever i reaches its final position toward the work, as
described, the dog g, comes into position on the surface 2 of the bearing or slide,
and forms a rigid abutment or locking device, the tool being held by the bolt h,
the rest 16 and dog 7, in accurate adjustment to restrain any longitudinal motion
of the bearing or slide or tool away from the work while the cutter is acting.
The pawl 18 is shown in Figs. 1, 2, 3, 5, and 25, it is formed on the lower end
of an arbor 21, fitted to turn in a bearing 22 attached to the lever 1; a suitable
spring 23, located in a cavity in the bearing 22, is attached to the lever I by one
end, and, by the other end, to a projecting arm 24 on the arbor 21, and serves, by
the elastic reaction of the spring, to press the pawl 18 toward the tool to engage
in the notches 46 between the cutters of the tool z.
The stock has fixed to it a block 19 having a cam surface 20, against which
a tail of the pawl 18 acts, as the tool arrives in its operative position, the contact
of said tail with said cam surface turning the pawl 18 aside and disengaging it
from the acting face of the cutter with which it just operated.
This cam surface 20 retains the pawl 18 out of operation while the lever is in
its extreme forward position, but shortly after the said lever has been started upon
its outward movement the tail of the pawl retires from the cam surface 20 letting
the spring 23 force the pawl against the side of the cutter with which it is next
to co-operate and finally the pawl passes the face of said cutter and is thrown into
the space ready to engage the said cutter when the movement of the lever is
reversed.
Fig. 16 shows a modification of this invention wherein the pawl marked 18 turns
on a horizontal arbor 28, journaled in a bearing 29 of the lever i, and in Fig. 17
the pawl shown is formed on the lower end of a spring 30, secured to the side on
the lever i, the pawl being guided by a dowel 31, inserted and fastened in the
lever i on which the pawl can slide freely toward and from the lever i as it engages
and disengages from the notches in the cutter z but compels the pawl to move
with the lever i as it is reciprocated, downward from the work.
In these last two described forms the locking action between the surface of the
pawl, and the surface of the tool, is avoided, the resulting effect of drawing the
tool step after step to bring one after the other of said cutters into operative
position is the same in each case.
Figs. 10 and 11 show modified forms of tools, and in these forms, the several
series of cutters on the tools 32 and 33, are like those marked z, previously
described, and are so constructed and combined as to act simultaneously, the
cutters being so proportioned as to their length that each cutter cuts a less amount
or makes a thinner chip; the cutters of the tool 32 and 33 are made preferably
separate from the tool, and securely attached thereto to co-operate with it.
These cutters are shown attached to the side of the tool and they rotate and
co-act with it, serving to subdivide the metal removed into thinner layers or chips
thus diminishing the stress upon each cutter, the resistance to the action of the
cutters being approximately in the ratio of the square of the thickness of the
chip; these tools 32 and 33 are preferably for facility or manufacture made
separately from the cutter z, but may be formed integrally therewith. Cutting
points of the tools are shown in enlarged scale in Figs. 12 and 13. Figs. 20
and 31 are projections of the outlines of the several notched points of the tool,

page_text: drawn, however, on an enlarged scale, that marked 34 cutting first and taking off
a broad chip at the same time when the material e has its full diameter, that
marked 35 takes a narrower chip of smaller thickness, the bar having been reduced,
and so on, until the apex 44 is reached, when a minimum shaving is taken, leaving
the work in finished condition.
During this operation, all undue torsional stress and springing or permanent
torsion of the material is avoided, and substantially perfect accuracy of pitch
is attained or effected for the finished screw.
To sharpen the tool the heels 15 (all uniform in shape as stated) may be suitably
supported, and the surface 14, constituting the acting face of each cutter, (sec
Fig. 8) may be ground to a gauged height from the heel, and owing to the peri-
pheral portion of each tool being of exactly the same thickness from the cutting
edge to the heel, it will be obvious that the grinding of the cutter in no way
modifies or changes its shape to at all interfere with the shape of the groove to be
made by the cutter.
The surfaces of the cutters are of regular geometric form and the tool is sus-
ceptible of being cheaply and accurately produced and finished by mechanical
grinding after the hardening and tempering processes, and consequently the tools
are capable of exact verification as to accuracy, and this being done by machinery
entirely independent of manual skill. When the tool is put in use, and it has
been once properly adjusted, the operations of forming the screw thread may be
done without any further attention than simply to move the lever-back and forth
and there is no perceptible delay between the operation of one and the next cutter
of the tool.
Each cutter, it will be understood, has only a limited and moderate amount of
work to perform, and to do this work it is not kept in operative position long
enough for it to become injuriously heated, and each cutter once used to make a
cut has ample opportunity to cool before it is again called into operation, and
consequently owing to this facility of having a cutter of proper temperature always
ready for use, it becomes practicable to rotate the work at a higher speed, and
the final or finishing touch may be made by a cutter constantly sharp, and The last
cutter may take off a finer shaving, thus insuring the highest accuracy of form,
dimension and finish of the screw thread. Several dises or tools with properly
graduating lengths of cutters may be fastened together to operate simultaneously.
The same stock and means for operating them may be used to support several
tools, and as the tools herein described will constitute separate merchantable
articles, they varying according to the particular number of cuts to be made by
each tool, the said tools become new articles of manufacture and are herein claimed
as such.
The actuating devices for imparting a rotative step by step movement to the
tool, and for sliding it to and fro, as described, in the stock, with relation to the
work, are novel, but this invention is not limited in all cases to exactly the
mechanism shown for effecting these movements and it will be obvious that these
devices may be variously modified in shape without the exercise of invention, and
yet operate as described and be within the scope of my invention; and so also in
the claims in which the actuating devices for the tool appear specifically, the
invention is not necessarily limited to the exact construction shown for the tool,
so long as its cutters vary in length or present peripheral portions varying one
from the other in thickness.
Having described my invention, what I claim, and desire to secure by Letters
Patent is
1. As a new article of manufacture, a tool for threading metal consisting of a
disk, having a series of integral cutters, each cutter having a heel, and interspaces
between the cutiers, the several cutters being of progressively increasing radial
length from the axis of the tool, the peripheral portion of each cutter being from
its cutting edge to its heel substantially uniform both in thickness and radial

page_text: length, and susceptible of sharpening by grinding of the acting face without
change of profile, the peripheral portions of the series of cutters however, varying
in thickness and constructed to operate substantially as described.
2. In an apparatus for cutting screw threads, the following instrumentalities,
riza tool composed of a disk having at its periphery the profile of the thread
to be produced and notched to form a series of integral cutters, said cutters vary-
ing in length as described, each cutter having a heel, a tool stock, a moveable
bearing mounted therein, a pivot to receive the said tool rotatably, means to move
the said bearing with its pivot and tool toward and from the work, a rest co-
operating with the heel of each cutter to support it while in operation and means
to retain the bearing forward with the cutter in operative position, substantially
as described.
3. In an apparatus for cutting screw threads, a stock, a bearing or slide mounted
therein and containing a pivot, a tool mounted rotatably on said pivot, said tool
having a series of cutters of varying length integral therewith, a rest mounted on
said stock, a lever free to turn on said pivot, and fulcra for said lever, and means
controlled by said lever to intermittently engage and turn said tool on said pivot,
the movement of said lever in one direction withdrawing the cutter from the work,
and in the opposite direction putting the cutter into operative position, with its
heel against said rest, substantially as and for the purpose described.
4. In an apparatus for cutting screw threads, a stock, a movable bearing mounted
therein, and a pivot fitted therein, a tool mounted rotatably on said pivot said tool
having a series of cutters of progressively varying length thereon, a rest mounted
on said stock, a lever free to turn on said pivot, and fulcra for said lever,
and means controlled by said lever to intermittently engage and turn
said tool on said pivot, the movement of said lever in one direction
withdrawing the cutter from the work, and in the opposite direction
putting the cutter into operative position, with its heel against the rest, and means
to adjust the said rest, substantially as and for the purpose described.
5. In an apparatus for cutting screw threads, a stock, adapted to be attached
to a tool post of an engine lathe, a bearing having a bolt or pivot, a tool having
a series of cutters of progressively greater radial length, said tool being mounted
rotatably on said pivot, a rest mounted on said stock, and adapted to successively
receive against it, and support the heels of the said cutters, means for locking
said bearing or slide in said stock with the tool in operative position with relation
to the work, and by reverse motion to disengage said locking device to release said
bearing or slide, and means to intermittently turn said tool about said pivot to
bring successively the several cutters of the series into operative position, sub-
stantially as and for the purpose set forth.
6. In an apparatus for cutting screw threads, a tool having a series of cutters
thereon, said cutters increasing progressively in radial length from the axis of
said tool, said tool presenting at its periphery notches between the cutters, and
a pivot to sustain said tool rotatably combined with a lever having a pawl, said
pawl in the movement of said lever in one direction operatively engaging said
tool and rotating it one step about its pivot, substantially as described.
7. In an apparatus for cutting screw threads, the following instrumentalities,
viz.a tool-post, a stock carried by said tool-post, said stock having applied to.
it, a movable bearing, a pivot mounted in said bearing and extended through the
said stock, a tool mounted rotatively on said pivot, said tool having a series of
cutters varying progressively in radial length, the peripheral portion of each tooth
being of substantially uniform thickness from its cutting edge to its heel, the
peripheral portions of succeeding cutters of the series being of gradually less
thickness, a lever to receive the pivot extended through said stock, and suitable
fulcra for said lever and a pawl carried by said lever, the said lever in the first part
of its stroke in either direction turning on said bolt or pivot, and thereafter by
contact with said fulcra moving the bolt or pivot with the lever, and effecting the
sliding movement of the tool from or toward the work as may be, the said lever in

page_text: one of its strokes causes said pawl to engage said tool and partially rotate it about
said pivot sufficiently to place another cutter into operative position, substantially
as described.
8. In an apparatus for cutting screw threads, the following instrumentalities.
riza tool adapted to be carried by the tool carriage of an engine lathe, said
stock having applied to it a movable bearing, pivoted in said bearing and extended
through the said stock, a tool mounted rotatively on said pivot, said tool having.
a series of cutters varying progressively in radial lengths, the peripheral portion
of each cutter being of substantially uniform thickness from its cutting edge to
its heel, the peripheral portion of succeeding cutters of the series being of
gradually less thickness, a lever to receive the pivot extended through said stock,
and suitable fulcra for said lever and a pawl carried by said lever, the said lever
in the first part of its stroke in either direction turning on said pivot, and there-
after by contact with said fulcra moving the pivot with the lever and effecting
the sliding movement of the tool from or toward the work as may be, the said lever
in one of its strokes causing said pawl to engage said tool and partially rotate it
about said pivot sufficiently to place another cutter into operative position, and a
rest carried by said stock, said rest receiving upon it the heel of a cutter prepara-
tory to the arrival of the tool in position to place and support a cutter in operative
position with relation to the work, substantially as described.
9. In an apparatus for cutting screw threads, the following instrumentalities,
riza stock adapted to be carried by the tool carriage of an engine lathe, said
stock having applied to it a bearing and a pivot extending through the said stock,
a tool mounted rotatably on said pivot, said tool having a series of cutters varying
progressively in radial length, the peripheral portion of each tooth being of sub-
stantially uniform thickness from its cutting edge to its heel, the peripheral
portions of succeeding cutters of the series being of gradually less thickness, a lever
to receive the pivot extending through said stock, and suitable fulcra for said lever,
and a pawl carried by said lever, the said lever in the first part of its stroke in
either direction turning on said pivot, and thereafter by contact with said fulcra
moving the pivot with the lever and effecting the sliding movement of the tool
from or toward the work as may be, the said lever on one of its strokes causing
said pawl to engage said tool and partially rotate it about said pivot sufficiently to
place another cutter into operative position and a rest carried by said stock, said
rest receiving upon it the heel of a cutter preparatory to the arrival of the tool
in position to place a cutter in operative position with relation to the work, and
a suitable locking device co-operating with said bearing to lock the same fixedly
in its forward position to prevent any retreat of the cutter while operating to
groove the work, substantially as described.
10. In an apparatus for cutting screw threads, a tool having a series of separate
cutters increasing progressively in radial length, a pivoted support on which said
tool is rotatably mounted, means to bodily move said support and the tool thereon.
and to automatically effect a step by step rotation of the tool on its support, and
a fixed rest against which the heel of each cutter is brought successively by move-
ment of the tool into operative position substantially as described.
11. In an apparatus for cutting screw threads, a tool having a series of separate
cutters increasing progressively in radial length, a reciprocable support on which
the tool is rotatably mounted, means to rotate said tool on its support, a common
actuating lever, connections between it and said support and the means for rotating
the tool, whereby swinging movement of said lever reciprocates the support and
tool bodily and also effects a step by step rotation of the tool on said support, and
a fixed rest against which the heel of each cutter is brought successively by the
movement of the tool into operative position and supported during the cutting
operation, substantially as described.
12. In a tool for cutting screw threads, two or more disks each having a series
of cutters of progressively increasing radial length from the axis of the tool, the
peripheral portion of each cutter being from its cutting edge to its heel substan-

page_text: tially uniform both in thickness and radial length, the said disks being secured
to each other with the cutters of each to act simultaneously and the radial length
of each series of cutters being such that the cutters of each disk shall be longer
than the adjacent preceeding cutters as and for the purpose set forth.
1000
ated this on Septembv.
HERMAN DOCK.
By George Downing & Sons,
Chartered Patent Agents, 8, Quality Court, London, W.C.