IMPROVEMENTS IN TWIST DRILLS
Year: 1884

page_text: I, ALBERT SÖDERSTRÖM, of Stockholm, Sweden, Engineer, do hereby declare the
nature of my said Invention for "IMPROVEMENTS IN 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 object of these improvements is to produce twist drills more advantageous
as regards the rapidity and precision of their action, as well as more easily
sharpened or kept in working order, than those hitherto in use.
In the accompanying Sheet of Drawings:
Fig. 1 is a longitudinal elevation of a twist drill, illustrating some of these
improvements.
Fig. 2 an end elevation of the same.
Fig. 3 a cross section through the line A A Fig. 1.
Fig. 4 an end elevation, and Fig. 5 a longitudinal elevation of a spiral tool
employed for their repair.
Fig. 6 an end view, and Fig. 7 a longitudinal elevation of a twist drill,
illustrating the balance of these improvements.
My twist drills are to be distinguished from those made use of actually by the
following characteristic features: first, they are provided with but one single'twist
or spiral 1 which is both deeper and wider and consequently has a larger area or
section for the passage of the borings; second, their cutting edges 2 radiate from
the center of the drill, see Fig. 2 & 6; I am aware that twist drills for wood
have been made, with a single spiral or twist, but in this case the cutting edge of
these boring drills has been made differently from that of my improved drills;
third the cutting edge at the bottom of the drill does not extend to the center, as is
the case with those in actual use, hence during its action, it leaves at 3 a small
central core unattacked by the drill, which core corresponds with the depth of the
hole bored, in certain cases when operating on certain metals the length of the said
core exceeds the depth of the hole bored; in the above mentioned figures, I have
shown a cutting edge which leaves a central core of a given diameter, but the
length of this cutting edge and consequently the diameter of the core thus formed
may either be diminished or increased according to circumstances, fourth, the
point 4 of the cutting edge is rounded off, as shown in Fig. 2 & 6, in view
of preventing its being so readily broken off, as with the drills as the actual make,
with a sharp angular edge, and also of making a cleaner cut.-Fifth. in order to

page_text: ensure the proper action of these new drills and also to prevent their being forced
in the hole being bored, as well as their sticking fast therein, from a certain point
at the bottom, say from 6, on the line 5 to 6, I diminish the diameter of the drill
upwards, say about one fiftieth of its diameter, see Fig. 1 and 7, for the purpose of
ensuring the latter to turn freely in the hole bored, and then I reduce to the same
diameter, either with a file, or in any other appropriate manner, the part of its
circumference extending from 7 to 4, see Fig. 4 and 6, the complementary untouched
of this circumference serves as a guide for the drill and determines the diameter
of the hole being bored. In practice, before performing this latter operation, I
consider it advantageous to cut out the twist or spiral, by means of a circular cutter
or any other appropriate tool, and. also to adjust the cutting edge to the required
angle. Sixth, in order to avoid the expense of making the larger kinds of drills
entirely of fine steel, I have recourse to an independent cutter 8 made of the best
steel, which I key on the end of the drill, see Fig. 6 & 7, and on the inner face of
which, I form a projection 9 for the purpose of maintaining the rigidity of the
cutting and of preventing its being broken, whilst at work, in this case, the stem
of the drill can be made of an inferior quality of steel or even of tough good iron.
In order to maintain in good working condition drills made in accordance with
the five first mentioned heads, (the cutting edges only of which are hardened and
tempered in the first case), when these cutting edges have been worn, they are
repaired or rendered efficient for work, by percuting their extremities with a small
hammer and especially. to their cutting edge and by readjusting in the lathe the
segmental part of larger diameter, extending from 7 to 4, see Fig. 4, & 6; in order
to ensure the proper accuracy of this latter operation; it is indispensable to make
use of a shell 10 in cast iron or other appropriate metal, corresponding exactly at
its two extremities with the external forin of the drill, and the surface of which is
*smeared with a coloured coating, such as red, and which when the drill is laid in
the shell shows clearly by deficient contact, the places that have to be rectified.
Having now particularly described and ascertained the nature of the said
Invention, and in what manner the same is to be performed, I declare that what
I claim is :
:
First. Twist drills constructed with one single spiral groove, with a right angle
cutting edge, that is to say, radiating from its center, with a free central space, that
is to say, forming or leaving a central core of untouched metal, with a rounded
cutting edge and with the end forming a seginental guide of a larger diameter
than the rest of the drill, as above described and illustrated in Fig. 1, 2. and 3 of
the accompanying Drawings.
Second. Especially for larger drills, a cutter keyed on the end of these tools, as
above described and illustrated in Fig. 6 and 7 of the accompanying Drawing, and,
Third. The cast iron shell 10 for repairing or readjusting drills after wear, as
above described and illustrated in Fig. 4 and 5 of the accompanying Drawing.
Dated thia Sixth day of May 1884