IMPROVEMENTS IN THE MANUFACTURE OF TWIST DRILLS
Year: 1884

page_text: I CHARLES CARTER of Lambeth Engineer do hereby declare the nature of the
said Invention for IMPROVEMENTS IN THE MANUFACTURE OF TWIST DRILLS to be
as follows:-
The objects of my Invention are to make drills, known generally under the
title of twist drills in such a way that they can be made very much cheaper and
much stronger than they can be by the present means.
With these objects in view I take bars of steel of suitable quality an'l I divide
them into two classes the fine or small diameter drills up to about 3/4" diameter I
treat in one way and those of a larger diameter I treat in another way. It is not.
a necessity that the dividing diameter between the small diameter and the large
diameter drills should ³/" but I prefer to use about that figure as my dividing
line and give it here by way of illustration. In making the finer diameter drills
I take a bar of steel rolled to the diameter I require and round in cross section
and then I draw it through hard metal templates or dies so that a double groove
is formed along the bar. When the grooves are made the edges are not as sharp
as they ought to be. With this in view I prefer to have the bars of steel of a
larger diameter after they are grooved than the finished drills I am making.
Then after I have grooved the steel bars I size them to gauge or to a standard size
either by lapping or filing or turning or other suitable means. This sizing of
course may be done after the bars are twisted instead of before.
These grooves can be made any suitable shape and it will be noticed that they
are formed in the direction of the "flow" of the steel and the skin of the bar is
not injured both these are important features in my Invention.
Having grooved my bar and sized it (or the sizing may be done after twisting)
I proceed to twist it to any suitable pitch-for instance the pitch required to cut
brass is different to that required to cut wrought or forged iron and that again is
different to the requirements for cutting cast iron. In order to give this twist I
place one end of a bar in the headstock of a machine and the bar is run through
the centre of a wheel working on a travelling guide by means of geared wheels
any speed may be given to the traveller and any relative rotary speed may be
given to the wheel which twists the bar.
There are many mechanical ways of arranging to give this twist to the bar and
I do not claim any special way but the method herein before mentioned is one I
prefer to use. Of course the bar may be pulled through a die and the die made

page_text: to turn and give the requisite twist-and the twisting may be effected at the last
operation of drawing the grooves.
In making twist drills of the larger size i.e. which are too large in diameter to
be conveniently drawn I prefer to roll them as though I was rolling round bars
but I leave suitable projections in the gates of the rolls which embed themselves
into the bars that are being rolled. These projections are of such a size and shape
that they make grooves in the round steel bars which I require in my twist drills.
The length of the projections is the same as the length of the twist in the drills
(making allowance for the loss of length in twisting) and the length between the
projections in the gates of the rolls is equal to the length of the shanks of the
drills. Or I make the projections in the gates of the rolls and the distances
between them double the above lengths and thus make the grooved parts and the
round parts of the steel bars double the length required for the twist of the drills
and also for the shanks. I then cut the bars across the centre of the grooved
parts and the centre of the round parts into their proper drill lengths, either before
or after sizing or before or after twisting.
The sizing and twisting operations are performed as hereinbefore described.
Another mode of grooving round steel bars necessary to the making of twist drills
by my Invention is to put a suitable length of round steel bar into a metal mould
sliding on guides and above and below to have two swages (one to be fixed and the
other actuated by steam, hydraulic or other power). The moveable swage falls on
the bar in the mould (which has two openings to allow the two swages to make
impact with the steel bar) and drives it on to the fixed swago. The form of these
swages in cross section and in length-is such that they groove the bar to the form
I require in my twist drill. This swaging operation may be done vertically or in
any other direction. The room for the bar in the mould is regulated by the
Bize of the grooves so that when they are finished the bar shall practically fill
the mould.
There is another method which may be employed. I take a finished, polished
straight bar of round steel and cut grooves in it with suitable cutting tools and
then baving twisted it I cut it into any suitable lengths of twist drill steel as in the
case of the small diameter drawn steel herein before mentioned.
There may be other ways devised to make grooves in straight bars of round
steel so that they can be sized and finished and twisted into twisted drill steel or
twist drills as hereinbefore described without interfering with the objects of my
Invention which are to groove straight bars of round steel and then to size finish
and twist them (the twisting and sizing operations being done either of them
first). Of course the twisting may be effected when the steel is either hot
or cold.

page_text: :
I CHARLES CARTER of Lambeth Engineer do hereby declare the nature of my
Invention for IMPROVEMENTS IN THE MANUFACTURE OF TWIST DRILLS and in
what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
The objects of my Invention are to make drills known generally under the title
of twist drills in such a way that they can be made very much cheaper and much
stronger than they can be by the present means.
In making twist drills according to my Invention I take bars of steel of suitable
quality and of convenient section (by preference round) and I divide them into
two classes. The fine or small diameter bars I treat in one way and those of a
larger diameter in another way. It is not a necessity that the dividing dimensions
between the small and large diameter bara should be any given figure. It can and
may vary from time to time. In making the finer diameter bars into twist drills
I take a bar of steel rolled to the size I require and then I draw it through metal
templates or dies so that a double groove is formed along the bar. These grooves
are opposite one another. When the bar has been drawn to the diameter and
the grooves to the shape I require as shown at Figure 1 of the accompanying
Drawing the edges are not as sharp as they should be but are sharpened when
the bar is sized to its proper gauge or standard size (this sizing may be effected
immediately after the bars are grooved) but I find it more convenient to size them
after they are twisted.
It must be borne in mind that the grooves are formed in the direction of the
flow of the steel and the skin is not injured both these are important features in
my Invention. The grooves as shown in Figure 1 are not the precise shape they
should be in twist drills but I find that in twisting the bars the grooves become
more rounded. Having then grooved the bar I proceed to twist it to any required
pitch. The pitch of the twist depends on the work to be done for instance the
pitch required to cut brass is different to that required to cut wrought or forged
iron and that again is different to the requirements for cutting cast iron.
In order to twist the grooved bars I place one end of a bar in the headstock of
a machine and the bar is run through the centre of a wheel working on a travelling
guide by means of geared wheels. Any speed may be given to the traveller and
any rotary speed may be given to the wheel which twists the bar. There are
many mechanical ways of arranging to give this twist to the bar and I do not
claim any special way but the method hereinbefore mentioned is the one I should
desire to use. Of course the bar may be pulled through a die for instance the last.
die or template used in drawing the bar and the die made to turn and give the
requisite twist. When the twisting is finished the grooves shown in Figure 1
become more like the shape shown in Figure 2.
In making twist drills of the larger size i.e. any size which it is not convenient
to draw I prefer to roll them as though I were rolling round bars but I leave
projections in the gates of the rolls which embed themselves into the bars
that are being rolled. These projections are of such a size and shape that
they make grooves opposite one another in the round steel bars which I require
in my drills.
If it is required to form grooves the whole length of the bar the grooves are of
course continuously but if I am making drills with shanks then the length of the
projections in the roll gates is the same as the length of the groove in the drills

page_text: (making allowance in the case of twist drills for the loss of length in twisting) and
the length between the projections in the gates of the rolls is equal to the length
of the shanks of the drills or I make the projections in the gates of the rolls and
the distances between them double the above lengths and thus make the grooved
parts and the round parts of the steel bars double the length required for the
groove of the drills and also for the shanks. I then cut the bars across the center
of the grooved parts and the centro of the round parts into their proper drill
lengths. This may be done before or after sizing or before or after twisting in the
case of twist drills.
As hereinbefore mentioned the sizing of these bars of all sizes may be effected
before twisting but I prefer to twist them first in the case of twist drills.
The twisting is done as hereinbefore described in dealing with the smaller
diameter drills. Having grooved and twisted the bars or drills I size them by
lapping or turning or filing or other suitable means.
Another mode of grooving round or other section steel bars necessary to the
making of twist drills according to my Invention is to put a suitable length of
round steel bar into a metal mould sliding on guides and above and below to have
two swages (one to be fixed and the other actuated by any motive power). The
movable swage falls on the bar in the mould (which has two openings to allow
the two swages to make impact with the steel bar) and drives it on to the fixed
swage. The forin of these swages in cross section and in length is such that they
groove the bar to the form I require in my drill. This swaging operation may
be done vertically or in any other direction or convenient way. The room for the
bar in the mould is regulated by the size of the grooves so that when they are
finished the bar shall practically fill the mould.
The making of grooves in steel bars hereinbefore described by drawing rolling-
or forging for the purpose of making drills whether with or without shanks is
entirely new and the bars so treated may be sized and finished without being
twisted and used as straight drills.
There is another method which may be employed in the manufacture of twist
drills. I take a straight bar of round steel and cut straight grooves in it with
suitable cutting or grinding tools and then having twisted it I cut it into any
suitable lengths for use as twist drills as herein before described.
There may be many other ways devised to make grooves in straight bars of
round steel so that they can be twisted sized and finished into twist drills as
herein before described with or without shanks without interfering with the
objects of my Invention which are to groove straight bars of steel and then to
twist size and finish them (the twisting and sizing operations being done either
of them first) of course the twisting may be effected when the steel is either
hot or cold.
Having now particularly described and ascertained the nature my said
Invention and in what manner the same is to be performed I declare that what
I claim is, The manufacture of twist drills by first obtaining straight grooved
bars of suitable sections and then twisting them to the desired pitch, substantially
as above described.