Improvements in Twist Drills.
Year: 1892

page_text: Complete optrinitation p 1000 play
COMPLETE SPECIFICATION.
Improvements in Twist Drills.
I, AARON BURnside Shippee of the City of Providence in the State of
Rhode Island United States of America, Machinist, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
This improvement in twist drills, consists in an important variation in the form
of the spiral grooves, whereby the wings or parts between those grooves are made
stronger, and of a shape suitable to form cutting lips more advantageous for use.
The back of the wings or outer bearing surface of the drill, is lightly grooved to
improve the clearance and delivery of the chips made in drilling.
Fig. 1 is an elevation of the grooved portion of a drill.
Fig. 2 is a cross-section taken on line a, a, showing the shape of the main grooves
in section, and the shallow grooves on the outer surface.
The general form of the drill is the same as most of that class of drills; that is,
a cylindrical bar of steel c, having for about two-thirds of its length, two deep
spiral grooves or flutes a, a, made in opposite sides of it, forming between them two
wings d, d, connected together at the middle by a web; these wings constituting
the working part of the drill. The shank by which the drill is held in a chuck
or arbor, may be either straight with parallel sides, or tapering, as may be
preferred.
The shape of the grooves a, a, is made angular or V-shaped in cross section,
forming nearly straight radial sides, from near the centre of the drill to the outside.
The advantages of this shape, are that it gives straight cutting lips e, e, which can
easily be ground sharp, and an increase of substance and strength to the wings or
working part of the drill in cross section, which of course, makes the tool more
durable.
Another improvement consists in making two shallow, concave grooves n, n,
lengthways on the outside of the wings d, d, or outside of the drill, which grooves
have slight ridges s, 8, between them, running in the same direction. The drill is a
little smaller in diameter from the top of one ridge to the top of the opposite ridge,
than the diameter of the outer cutting edges of the wings, so that the top of the
ridges will clear the inner surface of the metal in boring a hole, as seen in Fig. 2,
in which the broken circle r, represents the hole being bored.
One advantage of the grooves n, n, is that being too shallow to carry the chips
made by the drill, they will form clear passages for the oil to reach the extreme
inner end of the drill, when the rush of chips back in the main grooves, would
prevent the oil from going in that way, especially in drilling deep holes, for in the
usual form where the back of the wing is sloped away from the cutting edge to the
other edge of the wing, the oil put on the wing is carried off into the main groove
to be carried back by the chips.
In very large drills, the number of grooves and ridges may be increased to avoid
making them so large as to weaken the drill or allow chips to enter.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
A twist drill having shallow grooves with ridges intervening between them, made
lengthways of the wings or parts of the drill between the delivery grooves, the tops
of said ridges being a little below or inside of the circle of the hole the drill will
make in use, substantially as set forth.
Dated this 26th day of February 1892.
AARON BURNSIDE SHIPPEE.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, Agents for the Applicant.