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Патент USA US2403861

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July 9, 1946.
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w,- F, KLEMM
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CENTER
DRILL
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‘2,403,861
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Filed Dec. ,18, 1944
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INVENTOR.
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577721717575.
2,403,861
Patented July 9, i946
' UNITED ‘ STATE
sPArENT
oFFicET I
2,403,861
‘ CENTElftHDRILQL
William F. Kleinm, Detroit, Mich.
Application December 18, 1944, Serial No. 568,634 7
3 Claims.
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This invention relates to center drills and par
ticularly to a center drill in which the cutting
portion is formed on a continuous curve provid
ing vertical relief for the end cutting edge of the
pilot portion.
(01. ‘ii-66) '
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Heretofore center drills were provided with a
’ ‘abovethe end cutting edges and with side cutting
edges which are disposed onva continuous curve
.with the cutting edges on the countersinking por
tion of the drill; to construct a center drill by
grinding the side cutting edges on a true arc struck
from' a center disposed above the end cutting
edges of the pilot portion and providing radial re
countersinking portion and apilot portion on the
lief to the side cutting edges‘ and vertical relief,
end of the body. The pilot portion was of con
to the bottom cutting edges; andin general to
ventional drill construction extending from the
end of a frusto-conical countersinking portion 10 provide a center drill which is simple in con
struction and economical of manufacture.
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which machined the hole drilled by the pilot to a
desired taper. Difficulty was experienced when
employing this type of center drill due to the small
Other objects‘ and features of novelty of the
invention will be speci?cally pointed out or will
become apparent when referring, for a better
pilot portion becoming heated and expanding in
the hole causing it to become broken by the ap 15 understanding of the invention, to the following
plied torque.
When the break occurred across
the small pilot ‘portion, it was di?icult to remove ,
description taken in conjunction with the accom
panying drawing wherein the single figure dis
closes a center drill embodying features of this
the broken part because of its being wedged in
invention and a workpiece having a center drilled
the hole. Various attempts were made to con
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struct center drills in some manner to overcome 20 thereby.
A center jdrill I0 is illustrated having a body
this dif?culty and some improved center drills
portion II and a cutting portion I2. The cutting
have resulted from this effort.
portion is made up of a countersinking portion l3
In practicing the present invention, a center
and a pilot portion M which blend into each other.
drill is formed by constructing'the countersink
ing and pilot portions in smooth continuous sec 25 Cutting edges l5 are provided in the countersink
ing and pilot portions by the flutes l6 machined
tions which blend with each other to have the
side cutting edges disposed in smooth continuous
therein to project into the body portion.
curves. Preferably the curves are arcs of a
circle struck from a center disposed above the ‘
cutting edges l5 are struck from an are I‘! about
The
a center 18 which is disposed above the end cut
end of the pilot portion to have the cutting end’ 30 ting edges IQ of the drill section. The distance
2! above the bottom cutting edges IQ of the pilot
of the pilot portion of greater diameter than the
portion M is substantially equal to half the
portion directly thereabove. This not only pro
diameter 20 of the pilot portion, that is to say,
vides a simple curve upon, which the side cutting
substantially equal to its radius. The portion of
edges are ground and relieved, but vertical relief
the center drill disposed on the line 22 upon which
is provided to the bottom cutting edges .of the
the center [8 is located is of the smallest diam
pilot portion. When the center drill becomes
eter. The portions of the center drill above and
heated during the operation, the body portion of
below the line 22 are of increasingly larger
the pilot portion cannot expand suf?ciently to
diameters.
engage the side of the hole cut by the end cut
Relief is provided to the cutting edges I5 in
ting edges, and breakage from this cause is ~10
the regular manner by tilting the tool toward
eliminated. The relief above the end cutting
the grinding element rearwardly of the cutting
edge of the pilot portion is useful in providing
edges as the grinding element is oscillated across
chip clearance which permits the free movement
the countersinking and pilot portions about the
of the chips upwardly in the flutes of the portions.
center l8. Vertical relief will be provided in the
should the pilot portion become broken, the
hole 23 cut by the pilot portion the same dis
clearance above the bottom cutting edges permits
tance above the line 22 that the end cutting edges
the broken end to be easily removed from the
l9 are disposed below the line. This vertical
drilled hole.
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clearance above the end cutting edges is pre
Accordingly, the main objects of the invention
vents the heat generated in the. cutting portions
are: to provide a center drill with cutting por
of the center drill from expanding the pilot por
tions having the side cutting edges disposed in
smooth curves; to provide a center drill with
tion a sufficient amount to cause it to bind within
countersinking and pilot portions which blend
the hole. The ‘breakage which normally occurs
due to the expansion of the pilot portion is there
into each other on a smooth curve; to provide a
pilot portion for a center drill with vertical relief 55 by eliminated and should the pilot portion be
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2,403,861
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come broken the clearance above the end cutting
edges I9 will permit the operator to quickly re
2. A center drill having a body portion, a coun
tersinking portion extending from said body por
move the broken portion thereof. The clearance
tion, a pilot portion extending from said coun
is further useful in permitting free movement of
the chips from the hole upwardly in the ?utes
I6 in the body portion and in the countersinking
and pilot portions.
The arcuate countersinking portion of the hole
readily receives the tapered end 25 of a center
26 and the circular line of engagement therebe 10
tersinking portion having an end cutting portion,
and said pilot portion being joined on a smooth
tween will be coined into a band of a width con
curve.
said portions having at least one ?ute therein,
the section above said end cutting portion and
below said countersinking portion being of less
diameter than said end cutting portion to pro
vide relief therefor, said countersinking portion
forming to the amount of pressure applied be
3. A center drill having a body portion, a coun
tween the center 26 and the work. The band pre
tersinking portion extending from said body por
vents the drifting of the center and work rela
tion, a pilot portion extending from said coun
tive to each other and is available after a hard 15 tersinking portion having an end cutting portion,
ening operation to accurately center the work
said portions having at least one ?ute therein,
piece without the requirement of a separate
the section above said end cutting portion and
grinding operation which is employed to re-locate
below said countersinking portion being of less
the center after the hardening operation.
diameter than said endvcutting portion to pro
What is claimed is:
20 vide relief therefor, the form of said countersink
v 1. A center drill having a body portion, a coun
ing portion and said pilot portion being such that
tersinking portion extending from said body por
a plane in the longitudinal axis of said body por
tion, a pilot portion extending from said coun
tion intersects said portions on an arc of a circle
tersinking portion having an end cutting por
struck from a center located in said plane and
tion, said portions having at least one ?ute there 25 spaced from the end cutting portion toward said
in, the section above said end cutting portion and
countersinking portion.
below said countersinking portion being of less
diameter than said end cutting portion to provide
relief therefor.
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