Improvements in Drills.
Year: 1894

page_text: Date of Application, 25th Oct., 1894-Accepted, 1st Dec., 1894
COMPLETE SPECIFICATION.
Improvements in Drills.
J, MOSES CARLYLE JOHNSON, of No. 19 Congress Street, in the City of
Hartford, County of Hartford and State of Connecticut, United States of
America, Mechanical Engineer, 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:-
My invention relates particularly to the class of drilling tools known as twist
drills, and the object is to provide a drill which will embody all of the several
features of construction required to produce a proper working tool and one that
will have the maximum durability and efficiency in use.
To this end my invention consists in the details of the several features of con-
struction embodied and combined in the drill, as more particularly hereinafter
described and pointed out in the claims.
Referring to the drawing
Figure 1 is a view in side elevation of a twist drill embodying my improvements.
Figure 2 is a side view of a rod or drill blank showing in dotted lines the taper
of the web of the drill.
Figure 3 is a detail view in cross section of the drill (on enlarged scale) on a
plane at right angles to the axis as designated by the dotted line x-x in Fig. 1
and looking toward the point.
Figure 4 is a detail view in cross section of the drill, on enlarged scale, on plane
denoted by the dotted line y-y in Fig. 1.
Figure 5 is a detail view in cross section of the drill, on enlarged scale, on plane
denoted by the dotted line z-z in Fig. 1.
:
The principle of construction underlying my invention is not restricted to any
one special form of spiral or angle of twist of the groove used, as the pitch of the
groove will depend upon the material for use on which the drill is intended. For
example, when a drill is to be used on soft steel exclusively one pitch will give the
best results, while a different pitch is required for a drill to be used on cast-iron,
brass or other metals.
It is well known that the web of a drill should be comparatively thin at the
point in order to hold the drill central and cause it to produce a hole perfectly
round and true, and it would be desirable if that same comparative thinness of web
could be continued to the shank, but such a drill is too weak to stand the strain
put upon it and an increased thickness of the web has been resorted to to strengthen
it along its length.
A drill is made from a cylindrical rod of metal, and the groove (usually spiral)
extends from the point to the shank.
In order to secure the best practical results in use a twist drill should not be
weakened by the grooves, usually two in number, and which extend spirally along
the sides of the drill and run out at the point and shank; the cutting angle of the
lip should remain normal and the drill should readily clear itself of chips formed
in cutting.
In the accompanying drawing the letter a denotes the shank of a drill embodying
my improvements, 6 the point of the drill, c, c' the grooves and d the web. The
grooves are formed in a spiral about the axis of the drill and are of uniform pitch

page_text: so that a drill may be readily sharpened so as to present the proper angle for
cutting at any point along the length of the groove that may be reached by wear,
and by repeated sharpenings of the drill at the point.
The web d of the drill is made of gradually increasing thickness from point to
shank end of the groove in order to provide sufficient strength, and this thickening
of the web is produced by, or results in, a decrease in the depth of the groove from
point to shank end, as shown at d¹, d' and d³ in the drawings. Each groove is left
of substantially uniform width along its length, and experiment has shown that this,
is sufficient to provide for a proper discharge of chips from the drill under most
conditions of use. Such a drill has all of the advantages required in a drill of this
class, and they are obtained by features of construction as recited which do not
embody or result in any disadvantages.
The cutting lip of the drill is bounded by the conical surface of the end and by
the inclined surface of the groove where it runs out at the point, and one factor
of the two elements forming the angle of the cutting lip is the angle of inclination of
the groove across the axis which is determined by the pitch of the groove and
varies with the pitch.
My improvement includes the maintenance of a constant angle by the use of a
uniform twist of the spiral, and by this a form of cutting lip of maximum efficiency
is maintained in the drills until they are entirely worn out, such form ensuring a
proper cutting under of the chips at all times and avoiding the excessive
pressure
required to force a drill having too obtuse an angle of cutting edge into its work
and avoiding the consequent rapid wear of such misuse.
In the drill of the prior art which has a web of increased thickness the groove is
formed gradually shallower from the point toward the shank, but in such a drill
the chips will become clogged, and to avoid this an increased pitch of the grooves
has been given. This increase pitch causes a constantly varying angle of the
cutting lip as the drill is worn down and is a serious objection.
ID my constant angle drill a substantially uniform width of groove from point to
shank is obtained by a gradual variation of the angle of the cutters with reference
to the axis of the drill as the groove is milled, a uniform speed of rotation of the
drill being maintained to produce a groove of uniform pitch. This variation of the
angle of the cutters prevents the groove from becoming narrower toward the shank
of the drill, as would be the case if a fixed angular relation of the cutters to the
axis of the drill were maintained while they were being gradually moved away
from the axis of the drill to produce a gradually increasing thickness of the web,
and provides sufficient cross-sectional area of the groove at all parts of its
length for the proper clearing of the chips, and this without impairing the efficiency
of the cutting lip at any point by changing the pitch of the groove, or any
weakening of the drill by a thinning of the web.
In my improved constant angle drill the contour, angle and area of the grooves
at all parts of its length are proportioned to combine the maximum torsional
strength, the most effective chip clearance, and the best form of cutting lip.
My improved drill combines the several features of constant cutting angle,
constant pitch, uniform width of land, and web of increasing thickness from point
to shank whereby the maximum of strength and of cutting efficiency is obtained.
The drill is cleared or relieved by milling off the land or that portion of the
drill between the grooves so that there is an inclination of about one-half degree
from the cutting lip back to the opposite end of the land as is clearly shown
in the sectional views in the drawings, and this clearance is constant and uniform
along the length of the land.
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 :
,

page_text: uniform pitch and of substantially uniform width along their length from the point
to the shank of the drill, and having also a web of increasing thickness from point
to shank, all substantially as described.
MOSES CARLYLE JOHNSON.
D. Young & Co.,
11 & 12, Southampton Buildings, London, w.c.,
Agents for the Applicant.