Iм- PROVEMENTS IN SCREW TAPS
Year: 1874

page_text: LETTERS PATENT to Hunter Henry Murdoch, of No. 7, Staple Inn, in
the County of Middlesex, Patent Agent, for the Invention of "Iм-
PROVEMENTS IN SCREW TAPS."-A communication from abroad by
Bernard Lictar, Mechanic, and Joseph Hippolyte Dupuis, Merchant,
hath of Reussola in the Kingdom of Balcium
Sealed the 8th April 1875, and dated the 11th December 1874.
PROVISIONAL SPECIFICATION left by the said Hunter Henry Murdoch
at the Office of the Commissioners of Patents, with his Petition,
on the 11th December 1874.
I, HUNTER HENRY MURDOCH, of No. 7, Staple Inn, in the County of
Middlesex, Patent Agent, do hereby declare the nature of the said In-
vention for "IMPROVEMENTS IN SCREW TAPS," to be as follows:-
This Invention, as communicated to me, relates to the construction of
screw taps for cutting internal screw threads in the holes in screw boxes
or nuts, and metal or other plates, or other articles.
In constructing screw taps according to this Invention the threaded or
screwed part of the said taps instead of being of circular transverso

page_text: section throughout its length, as in ordinary screw taps, is of circular or
nearly circular transverse section at one end, and gradually assumes in
section a curvilinear triangular shape, the three sides of which curvi-
linear triangle are by preference arcs of circles, which are described
each from a different centre, and are therefore excentric to the axis of
the tap. Longitudinal grooves are made in the said taps on one side of
cach of the points or vertices of the said triangular parts, the said
grooves extending in straight lines, parallel or nearly parallel to the axis
of the tap, throughout the length of the-said tap, the said longitudinal
grooves being for the purpose of forming cutting edges to the tap, and
channels for the escape of the cuttings or shavings produced in forming
the internal screw threads of nuts or other articles.
SPECIFICATION in pursuance of the conditions of the Letters Patent
filed by the said Hunter Henry Murdoch in the Great Seal Patent
Office on the 10th June 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HUNTER
HENRY MURDOCH, of No. 7, Staple Inn, in the County of Middlesex,
Patent Agent, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Eleventh day of December, in the year of our
Lord One thousand eight hundred and seventy-four, in the thirty-eighth
year of Her reign, did, for Herself, Her heirs and successors, give and
grant unto me, the said Hunter Henry Murdoch, Her special license
that I, tho said Hunter Henry Murdoch, my executors, administrators,
and assigns, or such others as I, the said Hunter Henry Murdoch, my
executors, administrators, and assigns, should at any time agree with,
and no others, from time to time and at all times thereafter during the
term therein expressed, should and lawfully might make, use, exercise,
and vend, within the United Kingdom of Great Britain and Ireland,
the Channel Islands, and Isle of Man, an Invention for "IMPROVEMENTS
IN SCREW TAPS," a communication to me from abroad by Bernard Lictar,

page_text: Mechanic, and Joseph Hippolyte Dupuis, Merchant, both of Brussels, in
the Kingdom of Belgium, upon the condition (amongst others) that I,
the said Hunter Henry Murdoch, my executors or administrators, by an:
instrument in writing under my, or their, or one of their hands and
scals, should particularly describe and ascertain the nature of the said
Invention, and in what manner the same was to be performed, and
cause the same to be filed in the Great Seal Patent Office within six
calendar months next and immediately after the date of the said Letters
Patent.
NOW KNOW YE, that I, the said Hunter Henry Murdoch, do hereby
declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement thereof, that is to say :-
-
This Invention, as communicated to me, relates to the construction of
screw taps for cutting internal screw threads in the holes in screw boxes
or nuts, and metal or other plates, or other articles.
In constructing screw taps according to this Invention the threaded or
screwed part of the said taps instead of being of circular transverse
section throughout its length, as in ordinary screw taps, is of circular or
nearly circular transverse section at one end, and gradually assumes in
transverse section a curvilinear triangular shape, the three sides of which
curvilinear triangle are by preference arcs of circles, which are described
each from a different centre, and are therefore excentric to the axis of
the tap. Longitudinal grooves are made in the said taps on one side of
each of the points or vertices of the said triangular parts, the said
grooves extending in straight lines, parallel or nearly parallel to the axis
of the tap throughout the length of the said tap, the said longitudinal
grooves being for the purpose of forming cutting edges to the tap, and
channels for the escape of the cuttings or shavings produced in forming
the internal screw threads of nuts or other articles.
If preferred, screw taps constructed according to this Invention may
be made in cross section of the figure of a curvilinear quadrangle or a'
curvilinear polygon in place of the curvilinear triangle herein-before
described.
Having explained the nature of this Invention, I will proceed to
describe, with reference to the accompanying Drawings, the manner in
which the same may be performed,

page_text: Figure 1 represents in perspective the blank from which a conical
screw tap is to be made according to this Invention; Figures 2, 3, and 4
are transverse sections of the same taken through the lines AB, CD,
and EF respectively.
Figuro 5 represents in perspective the blank shown at Figure 1, after
the screw threads have been cut in it.
Figure 6 represents in perspective the finished screw tap, that is to
say, after it has been screwed, and after the longitudinal grooves have
been made in it; Figures 7, 8, and 9 are transverse sections of Figure 6,
taken through the lines AB, CD, and E F respectively.
a, Figures 1, 5, 6, is the head of the screw tap; b in Figure 1
represents the body of the blank.
It will be seen by reference to the sections shown in Figures 2, 3,
and 4 that the end AB of the blank is in transverso section of a
curvilinear triangular shape; at CD the curvilinear triangle is gradually
merging into a circle; and at EF the section is perfectly circular, as
seen at Figure 4.
Figure 5 represents the blank, Figure 1, after the screw threads c have
been cut in it.
At Figure 6 the blank, Figure 1, which has been screwed, as shown at 2
Figure 3, has had formed in it the longitudinal angular grooves d, d, the
shape of which grooves is best seen in the sectional views, Figures 7, 8,
and 9. The said grooves d, which are formed or cut one on the side of
each of the points or vertices x, y, z, of the curvilinear triangle (Figure 2),
are for the purpose of forming cutting edges to the tap threads c, and 2
channels for the escape of the cuttings or shavings produced in the
tapping process.
Figure 10 represents in perspective a three-sided tap constructed
according to this Invention, in which the cutting points of the tap are at
equal distances from the centre line throughout the length of its screwed
part; Figures 11 and 12 are transverse sections of the same through the
lines A B and C D respectively.
The form of the tap represented in Figures 10, 11, and 12 is somewhat
different from that of the conical tap shewn in the other Figures of the
Drawing, the end CD, Figure 10, being of curvilinear triangular section,

page_text: and the sides of the curvilinear triangular surface, shewn at Figure 12,
may be even more excentric to the axis of the tap than those of the
section shewn at Figure 11. a is the head of the tap; c, the screwed
part; and d, d, are the grooves. The form of tap herein-before last
described is adapted more particularly to the tapping of holes from the
bottom of which there is no outlet.
From an examination of Figures 7, 8, 9, 11, and 12 it will be readily
understood that in taps made according to this Invention only the sharp
or cutting ends or edges of the three-sided screw threads come into
direct contact with the metal parts to be cut out or removed in the
tapping process; the friction between the parts is therefore less than
when ordinary taps are used, and consequently less power is required for
the purpose.
The threads of the screws formed upon the said taps may be either
triangular, as shewn, or of other suitable shape, and when large screw
taps are made according to this Invention they may be made from blanks
having in transverse section the figure of a curvilinear, or quadrangle
of a curvilinear polygon in place of the curvilinear triangle herein-
before described.
Having now described the nature of the Invention, and the manner in
which the same is to be performed, I wish it to be understood that I do
not confine myself to the precise details herein-before described and
illustrated in the accompanying Drawing, as the same may be varied
without departing from the nature of the said Invention; but I claim as.
the Invention,—
Firstly. The construction of conical screw taps, as herein-before
described and illustrated in the accompanying Drawing, that is to say,
screw taps of circular or nearly circular transverse section at one end,
and assuming gradually in transverse section a curvilinear triangular
figure, such taps having a longitudinal groove formed on one side of each
of the points or vertices of the triangular parts, essentially as herein-
before described and illustrated in the accompanying Drawing.
Secondly. The construction of screw taps of curvilinear triangular
section throughout their length, with a longitudinal groove on one side
of each of the points or vertices of the triangular parts, essentially as
described and illustrated in Figures 10, 11, and 12 of the accompanying
Drawing.

page_text: Thirdly. The construction of screw taps of curvilinear, quadrangular, or
polygonal section, and either of circular section at one end, or of
curvilinear, quadrangular, or polygonal section throughout, a longitudinal
groove being formed on one side of each of the points or vertices of the
angular parts.
Thirdly. The construction of screw taps of curvilinear, quadrangular, or
polygonal section, and either of circular section at one end, or of
curvilinear, quadrangular, or polygonal section throughout, a longitudinal
groove being formed on one side of each of the points or vertices of the
angular parts.
In witness whereof, I, the said Hunter Henry Murdoch, have here-
unto set my hand and seal, this Tenth day of June, in the
year of our Lord One thousand eight hundred and seventy-
five.
Witness,
B. WILLCOX,
his Clerk.
H. H. MURDOCH. (L.S.)