Improvements in Screw-cutting Tools, such as Taps, Dies, and the like.
Year: 1897

page_text: Date of Application, 10th Aug., 1897-Accepted, 11th Sept., 1897
COMPLETE SPECIFICATION.
Improvements in Screw-cutting Tools, such as Taps, Dies, and
the like.
I, FRANK GLENN ECHOLS, of No. 57 Imlay Street, in the City and County of
Hartford and State of Connecticut, United States of America, Machinist, do hereby
declare the nature of this invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:-
This invention relates to Improvements in Screw-cutting Tools-such as taps
and dies-for forming internal and external screw-threads, and it has for its main
object the provision of an improved tool of this type by means of which screw-
threads may be cut easily and rapidly without breaking or distorting the same
and without injuring the tool used for the purpose.
In screw-cutting tools heretofore employed in which the teeth in a given
row are arranged consecutively, one tooth for each turn of the thread being
cut, the row of teeth form together a complete wing extending transversely of
the article being threaded so as to carry forward with the row of cutting faces
or teeth not only the chips formed thereby but also the lubricating material,
thereby wiping off substantially all of the lubricating material from the freshly-
cut surfaces and leaving only the clean metal in the path of succeeding cutting
faces or teeth of the tool.
In my improved tool, however, there are formed in each wing thereof numerous
blank spaces through which the chips, and especially the lubricating material,
may pass freely around the threading-tool while this is in use, the lubricating
material flowing around from one groove to another and thus lubricating the
freshly-cut surfaces immediately in advance of the cutting-teeth and with a
gradually-increased thoroughness and efficiency.
In order to attain this result and form these blank spaces between the teeth
of the several wings of the cutting-tool, I so dispose the cutting-faces that the
centers of adjacent teeth will be spaced at greater intervals than the pitch of
the thread to be cut, the preferred construction being one in which the teeth
in each wing are separated by intervals which are multiples of the pitch of said
thread.
Moreover, these teeth and the spaces therebetween are so located that some of the
turns of the thread of the tool will have a less number of teeth than the number
of wings from which the teeth rise, the teeth and the blank spaces preferably
alternating in each turn.
In the construction illustrated in the drawings, which is the one I prefer to
employ, I have shown in each view a screw-cutting tool having an odd number
of wings formed with teeth and blank spaces which are located in a single spiral
and alternate from end to end thereof, so that there will be a blank space in each
wing between the preceding cutting-tooth in the wing in advance of that con-
taining such blank space and the succeeding tooth in the wing in the rear of such
blank space.
By means of this organization of the teeth of the threading-tool relatively to

page_text: the blank spaces thereof I am enabled to obtain the greatest efficiency and the
best results, for the reason that after the tool has started there will be a groove
in the material operated upon between each pair of teeth of the tool, and through
this space the lubricant may flow freely and the chips pass during the whole of
the threading operation.
Owing to the fact that this intermediate groove between two adjacent teeth
of the cutting-tool is always present after the threading operation has begun,
the threads at opposite sides of the groove are permitted to yield sidewise toward
each other by reason of the mobility of the material being cut, so as to facilitate
materially the operation of the tool and prevent binding thereof.
It should be stated here that in my improved screw-cutting tool I am enabled
to make use of cutting-teeth having no side relief whatever, as there is always
a sufficient space between each pair of adjacent cutting-teeth to permit this
sidewise yielding of the screw-threads when pressure of the sides of the cutting-
teeth is applied thereto.
In the drawings accompanying and forming part of this specification, Figure
is a side elevation of a tap constructed in accordance with my improvements.
Fig. 2 is a transverse section of the same, the section being taken in the line 2-2,
Fig. 1. Fig. 3 is a developed view of the periphery of the cutting-tool or tap
shown in Fig. 1, this view illustrating the manner in which the cutting-teeth
and the blank spaces alternate. Fig. 4 is a sectional detail, on an enlarged scale,
showing the manner in which adjacent teeth operate to cut the outer sides of
adjacent threads which have a clear space or groove between them and are free
to move toward each other. Fig. 5 is a plan of a modification of my invention,
showing a separable die and die-stock, in which the former is constructed to
operate in the same manner as the tap herein before described. Fig. 6 is a
transverse section of the same, the section being taken in line 6-6, Fig. 5.
Fig. 7 is a plan of a solid die also embodying my invention; and Fig. 8 is a
transverse section of the same taken in line 8-8, Fig. 7.
•
Similar characters designate like parts in all the figures of the drawings.
As before stated one of the main features of my invention consists in spacing
adjacent cutting faces or teeth so that there will be a greater interval between
the centers of those teeth than the pitch of the thread that is to be cut.
Preferably the cutting-teeth are disposed in successive rows or wings in such
a manner that some of the faces of one row are followed by a blank space or spaces
in the following row.
Referring, first, to Figs. 1 to 3, inclusive, T designates in a general way a tap
of taper construction having five wings, (each indicated by W). The cutting-
teeth, by means of which the screw-thread is to be formed, may be located in any
manner within the scope of my invention, so long as the distance between the
centers of some of the adjacent teeth of the tool is greater than the pitch of the
thread to be cut thereby. In this case, however, the teeth, which are indicated
by t, are formed in rows, one row for each wing w, and are separated by blank
spaces or interdental spaces s, the teeth and the spaces alternating from end to
end of each wing. These interdental spaces are at all points of the full depth of
the teeth, have substantially flat bottom walls, and are preferably of such size
that the teeth in each wing are spaced at intervals that are multiples of the nitch
of the thread to be formed by the tool, the teeth in this case being disposed at
intervals twice that of such pitch. This will be clear by reference to Figs. 1
and 3; and, moreover, it will be seen by referring to Fig. 3, that the teeth and the
interdental spaces alternate also in the direction of the spiral, each turn of the
spiral having a series of alternating teeth and spaces in the wings of the tool,
and all of these teeth and spaces alternating throughout the whole extent of
the spiral from end to end of the tool, so that at every point in the cutting
operation a cutting-tooth, will be succeeded by an interdental space in the next
wing, and said space in turn will be succeeded by a tooth of the next following
wing.

page_text: In the operation of the tap shown in these figures one cutting-tooth comes
between two adjacent turns of the thread so as to cut the outer face or side of
each thread. The inner side of each thread faces the groove between these threads,
as shown clearly in Fig. 4, and no pressure is brought to bear upon these inner
faces at any point in the length thereof while the outer faces thereof are being
cut at corresponding points. Hence, the metal of the thread being cut is able
to support itself at any particular moment at a given point against force applied
only at one side of such point.
Heretofore this metal has had to support itself against displacement at both
sides, owing to the fact that it has been customary to plane opposite sides of the
thread at any particular point at the same time, and this action has usually
resulted in distorting or breaking off the edge of the thread, especially when the
material operated upon has been such as would not oppose much resistance to
the pressure exerted against it.
By means of my present invention the thread being formed is relieved of the
excessive pressure due to the combined action of tool-cutting teeth operating
simultaneously at opposite sides thereof and is thereby enabled to withstand the
action of the tool, so that any number of perfect threads may be formed easily
in metals, and under circumstances, in which threads have been made heretofore
only with great difficulty and after the loss of a large percentage of the work
and stock.
In Fig. 4 I have illustrated in detail, on an enlarged scale, the action of two
separated cutting-teeth upon two adjacent turns of the thread being cut thereby,
this view also illustrating the intermediate groove which forms a flowage space
for distributing the lubricant, permitting the escape of the chips, and relieving
pressure on the threads being cut. The material that is being threaded is repre-
sented here by B, and may be assumed to be a nut.
4-4 designate two adjacent threads which have been formed by the action
of the cutting-teeth, and 5 represents..the groove between those threads.
The blank space between the teeth t-t is indicated by 6, and is of the same
width as the mouth of the groove 5 in the material. One of the teeth, t, bears
against the outer face of the thread 4 and the other against the corresponding
face of the thread 4', but as there is no tooth of the tap between these threads
at this point there is no pressure upon the inner faces of the latter, and con-
sequently the metal of the threads 4-4 around the inner sides and at the
extreme points of these threads is not grasped between cutting-teeth, as would be
the case if the threads were formed by the ordinary tap.
It will be clear that, no matter what the material of the stock may be, the
base of each thread will exert a much greater resistance to displacement by
pressure applied only at one side of the thread than when opposite sides of the
thread are being cut at the same time and pressure applied thereto, and that
the material will be much better able to maintain its shape and position when
only one side thereof is cut at a time and the opposite side is left free to yield
during such cutting operation.
Another important advantage which I secure by my invention, and one that
is due directly to the presence of this groove between adjacent turns of the thread,
is that very much less relief of the cutting-teeth may be used, and that I may
entirely dispense with the side relief for the sides of the teeth. The result
of this is to give the tool greater stability in action and render it more durable,
thereby increasing the amount of work done by a tool of a given size and reducing
the cost of such work.
By thus overcoming the necessity for relieving the sides of the teeth I am
enabled to sharpen the cutting-faces indefinitely by grinding the cutting ends
of the same so as to keep the teeth perfectly sharp without changing the cross-
sectional area or form thereof.
It is particularly to be noted that the edges of the flat bottom walls of the
interdental spaces 6 act as knives and shave off the top of the thread as the tap

page_text: is driven through the article to be threaded, and thereby remove any metal that
may have been distorted or crowded out of place, owing to the mobility of the
metal in the thread-forming operation.
It is well known that in ordinary practice the cutting-teeth cannot be ground
away on their faces to any considerable distance without affecting materially the
size of the threads produced by the cutting-tool.
By making the cutting-teeth of full width from the front to the rear edge
thereof the tool can be turned backward freely without drawing chips between
the rear ends of the teeth and the work, which would result in binding the tool.
Such binding is common in taps and dies, especially in hand-taps, and is the
cause of much difficulty in the cutting of threads in many kinds of work, resulting
frequently in serious injury to the thread and sometimes in tearing it entirely
away.
In Figs. 5 to 8, inclusive, I have illustrated my invention in connection with
screw-cutting dies; Figs. 5 and 6 illustrate a separable or expanding die, and
Figs. 7 and 8 a solid one.
In Figs. 5 and 6 the cutters c correspond to the wings w shown in Figs. 1 to 4;
and the cutter-teeth alternate with blank spaces in each cutter, the teeth
and the spaces also alternating in the direction of the thread.
In Figs. 7 and 8 the wings w correspond to the wings w shown in Figs. 1
to 4; and the teeth are similar to those shown at t¹; but both the teeth t and
the teeth have concave faces instead of convex ones, as is the case with the
teeth. In this solid die the teeth t¹ and spaces alternate with each other
in each wing and also in the direction of the spiral or thread in which they are
located, the construction in these views and in Figs. 5 and 6 being similar in
every respect to that illustrated in Figs. 1 to 4, except that the dies are adapted
to cut external threads and the taps internal threads.
7
Screw-cutting tools, both in the form of taps and in the form of dies, made
according to this invention are found to operate with very much less power than
is required for screw-cutting tools of the old kinds; and I have also found that
screw-cutting taps, especially such as are used for tapping nuts and for similar
work, may be made shorter than they are ordinarily, while securing freer action,
requiring less power, and having greater durability, as indicated by a number
of tests of the invention with tools of a variety of sizes and kinds.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what I
claim is
1. A screw-cutting tool having an odd number of wings each equipped with
teeth having no side relief, and interdental spaces located in a single spiral and
.alternating from end to end of the working portion of the tool, said interdental
spaces being at all points of the full depth of the teeth and having flat bottom
walls in line with the roots of said teeth.
2. A screw-cutting tap having an odd number of wings formed with teeth of
full depth from the front to the rear edge thereof, and interdental spaces located
in a single spiral and alternating from end to end of the working portion of the
tool, said teeth having no side relief, and said interdental spaces being at all
points of the full depth of the teeth and having flat bottom walls, substantially
as and for the purpose specified.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.