Note: Descriptions are shown in the official language in which they were submitted.
~ 3240 ~ ~
BACKGROUN~ OF THE INVENTION
The present invention relates to drills and more
particularly to a cutting tip which is useful in connection
with a masonry drill assembly including a fluted shaft to
receive t~le tip ann carry away the chips generated by
rotation of the cutting tip.
lt is known in the art that pointed cutting tips are
commonly utili2ed in connection with masonry drills where
the cutting tip is inserted into the end of a helically
fluted shaft which is utili~ed to pick up and carry away the
chips generated by the rotation of the tip.
The cutting is dccomplished by means of rotation of the
tip as previously described, in a selected direction of
rotation, where in tlle prior art a cutting edge is
established on each side of the chisel edge of the tip by
the intersection of d leading face of the tip as defined by
the direction of rotdtion dnd d Srontmost surface of the tip
as defined by the direction of penetration, and where a
flank edge pardllel to the axis of penetration of the drill
is established on each side of the point by the intersection
of d leading face of tl-e tip and a sidemost surface of the
tip pardllel to the axis of penetration of the tip, and
where the intersections of said cutting edges and said flank
edges establish poin~s of the tip on each side of the chisel
edge, said points being tl~e locus of the initiation of and
~he most rapid progress of the chipping and attrition which
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causes the wear of the cutting edges and flank edges during
cutting. '
Prior art drill tips of the foregoing configuration are
known and have been manufactured by the Vermont American
corporation as well as many others. Prior art drills are
~nown that incorporate a chamfer of the cutting edge for the
purpose of increasing resistance to gross chipping, but at
the exDense of increased reSiStdnCe to penetration. ~o one
skilled in tlle art the said chaInfer produces whdt is known
dS d "negative rake." ~here are no prior art devices that
have uti1i2ed a chamfer to produce a negative rake on a
-flank edge of a masonry drill tip as provided by present
invention.
One example of a prior art masonry drill bit is shown
in U.S. Patent number 4,026,327 wllere a rotary percussive
drill bit is illustrated. In U.S. Patent number 4,243,113 a
drill bit somewhat similar to one arrangement provided by
the present invention is shown but without the chamfered
edges.
Other features of drill bits are shown in U.S. Patents
3,106,972 and 3,555,937 as well as British Patent 1,062,158
but non show a straicht forward masonry drill.
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suMMARr OF THE INVENTlOh
The preSent invention provides new useful, and
- inexpensive arrangements for improving the characteristics
of drill bits for stone and masonry, and particularly for
increasing the wear life of a drill bit utili~ed for
drilling holes in hard britt1e materials such as masonry and
rock and reducing the force required to advance the drill
bit.
In accordance with one feat"re of the present invention
it has been found tl,at in the case of masonry drill bits
and in particular~ drill bits of planar configuration
having a point and flank edges where the cutting edges are
advanced into the mdterial to be cut as the drill advances,
drill bit failure initiateS most often at the intersectionS
of the cutting and flank edges. Normally the wear then
develops a10ng tl-e leading cutting edges and the flank edges
and causes a receeding of the points of intersection and a
rounding of the two edges. Progression of the wear pattern
progressively increases the force required for penetration
until the force required is greater than the force
available.
It llas been une~Dectedly found that structures withjn
the scope of t~le prese~llt invention direct the ~ear at the
intersections of tlle ClItting edges and the respective flank
edges away from said intersections so that the result is
more uniform wear over a grea~er length of edge and a
geometry that prcvides qreater structual resistance to
chipping aIld major fractule
. I
1 32401 3
Arrangements within the scope of the present invention
further provide dril1 bits with strengthened flank edges
which have been found to unexpectedly greatly increase
useful drill iife.
Further it has been unexpectedly found that by
chamfering the flank edges the effectiveness of the drill
bit is improved in masonry and stone drilling.
In summary the present invention provides a cutting tip
to be carried by a drill bit for rotation in a first
direction and useful in drilling holes in for example
masonry and rock mateIials where the tip is planar and has
a chisel edge defined by first and second cùtting edges
intersecting with tlle chisel edge and third and fourth flank
edges where tlle leading edge of at least one of the flank
cutting edges determined by the direction of rotation is
chamfered at the leading edge.
~hile several arrangements within the scope of the
preSent invention are shown in the accompanying figure it
will be understood that various other arrangements also
within the scope of the present invention will occur to
those skilled in the art in view of the reading of the
disclosure set forth hereinafter.
1 32401 3
BRIEF DESCRIPTION OF T~E DRAWINGS
Examples in accordance with the present invention and
the prior art are shown in the accompanying drawings where:
Figure I is a perspective view of an example of a drill
tip in accordance with the present invention located in a
drill shank;
Figure 2 is d plan view of a prior art cutting tip;
Figure 3 is an elevational view of ~he cutting tip
shown in Figure 2;
Figure 4 is a view taken along a plane passing through
line 4-4 of Figure 3;
Figure S is a view taken along a plane passing through
lines S-S of Figure 3;
Figure 6A-6B are plan views of other prior art drill
bits;
Figure 7 is a perspective view of another example of a
prior art drill tip;
Figu~es 8A and ~a are plan and elevational
illustrations of an example of one drill tip arrangement in
accordance with the present invention;
Figures 9A-98 are plan views of other drill tip
arrangment within the scope of the present invention; and
Figu~-e 10 is a graphic illustrating the comparison of
the characteristics of drill bits within the scope of the
present invention with prior art drill bits.
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¦ DETAlLEi) DESCRIPTION OF rHE DRAwlNGS
¦ Referring first to Figure 1 a perspective illustration
¦ of d cutting tip within the scope of the preSent invention
¦ located in a drill 5hank as generally well known in the art.
¦ In Figure I a tip 1 in this case a tip with;n the scope of
¦ the present invention as described hereinafter ;s 10cated in
¦ a fluted shank member 26 and can be of for example
¦ tungsten carbide.
l Flutes 27 helical1y encircle shaft 26 and are provided
¦ for the reIlloval of clliI)s generated by the cutting edges of
¦ the tip I dS the 5IIdrt 26 rotates while being thrust by a
¦ feed force F into the nateridl being drilled.
l Figures 2-6B illustrdte drill tips dS known in the
¦ prior art. Figu e 2 is plan view of an example of one prior
¦ art tip~ and Figule 3 is ar elevational view of the same tip
hich is a solid defined Iy seveI- surfaces. Surfaces SA and
7A are symmetrically disposed on each side of a centerline
of rotation of the tiV so that the intersection creates a
l chisel edge 3 where the surfaces 5A 7A intersect at an
¦ angle less thall 180. Likewise the intersection of surface
SA with surface 4 defines cutting edge S while the
intersection of surface 7A with surface 4 defines cutting
edge 7. In tl-e arrangement shown in Figures 2 and 3
surfaces SA and 7A extend between surfaces 4 and 6 at an
angle B for example 15 to 30~ as illustrated in Figures
4 and S to define the clearances behind the cutting edges S
and 7 defined by tlle intersection of surface SA 7A and
lateral surfaces 6 and 4 respectively as shown.
1 32401 3
In the prior art arrangement il1ustrat~d in Figure I
and 2 flank surfaces IOA and llA which may be planar 3s
shown in Figure 2 are provided and flank edges IO and II are
provlded by the intersectlon of surfaces IOA, llA bnd
surfaces 6 and 4 respectively. Surfaces lOA and IIA may be
located at an ang1e C wit~ respect to surfaces 6 and 4 to
provide clearance bellind the flank tips IO and II as shown.
It is obvious that the extensions of cutting edges S
and 7 terminate at their intersection with flank edges IO
and Il to create points I3 and I4. In the case of a new
drill tip or dril1 tip with no wear, the cutting action is
performed by the cutting edges S and 7 and the diameter of
the hole is determined hy tlle distance between points I3 and
I4 where flank edges IO and II merely follow points I3 and
14. The cutting tip is of a hard material for example a
conglomerate of smdll hard partic1es appropriately bonded
together, for example, cemellted carbide which is cùrrently
; used.
Examining the fine structure at the points I3 and I4 it
will be recognized t~lat the outermost hard particle at each
is bonded to t~le body of the tip over less of its surface
than are the next adjacent particles and that the proportion
of the particle bonded to the body of the tip is a direct
function of the solid angle bounded by surfaces 7A 6, IOA
and similarly by SA, 4, llA. For example, as shown in
Figure 7 particle IS of which point I4 is one corner is
bonded to the body by three (3) surfaces whereas particle I6
is bonded by four (4) surfaces. Obviously particle IS at
point I4 5holI1d be more easily dislodged. -
~ 1 324~1 3
¦ The partic1es 15 and I6 can represent single hard
¦ partic1es or they can represent an aggregate of partic1es.
¦ During wear ùoth sing1e partic1es and aggregates of
¦ partic1es are dis10dged. Whether it is a single partic1e or
¦ the aggregate of partic1es that is dis10dged in a spec,ific
¦ event is dependent Dn a mu1ip1icity of conditions and events
¦ inc1uding constant fo~ces, impact forces, direction of
¦ forces, inhomogeneities in the material being cut,
¦ inhomogeneities in the cutting tip material, size and
¦ hardness of the cuttings from the workpiece relative to the
¦ size and hardIless of the hard particles and to the thickness
¦ and hardness of the borlding material in the cutting tip.
¦ Whatever the preciSe combination of wear mechanisms the
¦ resultant wear initiates at points I3 and 14 and growS.
¦ Ultimately, cutting edges S and 7 are blunted and flank
¦ edges I0 and lI become tapered so that the cutting tip
¦ becomes wedge shaped when seen in the elevation view. These
¦ changes cause an increased thrust required to penetrate the
¦ workpiece unti1 furtl,er use of the drill tip is no longer
l practical.
In accordance with one feature of the present invention
it has been unexpectedly found that the physical strength of
the cu~ting edges S and 7 at their extremities iS a 1arger
l than expected proportion of the total wear mechanism and
¦ that strengtIlening the extreme portions of cutting edges S
and 7 significantly increases the useful life o- the drill.
Other prior art configuration are also known as shown
in Figures 6A and 6B. In Figure 6A the 'flank surfaces are
l composed of two semicirclIldr surfaces 17 and I8 having a
1324013
diameter D2 equal to the diameter of the hole to be drilled
as the drill is rotated in direction F so the drill bit
flank edge is congruent to the surface of revolution caused
by drill rotation. Chamfered surfaces 19 and 20 are
angularly disposed so that their trailing edges clear the
surface of revolution. Figure 6B illustrates an
arrangement where semicircular flank surfaces 21, 22 are
provided with diameter D2 which is the diameter of the
drill bit, so the total flank surface are congruent to the
surface of revolution of the bit.
Referring now to Figure 1 which shows an assembly
using a drill bit within the scope of the present invention
shown in enlarged view in Figures 8A, 8B a principal
feature of drill tips within the scope of the present
invention as shown in Figure 8A, 8B is that the flank edges
lOA and llA, shown in Figure 2, and surfaces 17, and 18
shown in Figure 6A and surfaces 21, 22 shown in Figure 6
are replaced by chamfer surfaces 43, 44.
In accordance with a principal feature of the
present invention, the flank surfaces lOA, llA of the
example in the prior art shown in Figure 3 are modified by
chamfers 43 and 44 as shown to create new edges 46, 47 and
new edges 52 and 53 and a new set of cutting points 57, 58,
59, and 60 as shown in the Figures where points
corresponding to the points 59, 60 were not provided by the
prior art. As shown in Figure 8A, the chamfered surfaces
43 and 44 respectively form an included angle I with the
plane of their adjacent flank surface 62 or 61 of from 7.5
132~ol3
degrees to 70 degrees. Preferably, the angle I is 45
degrees.
~ S~
Similarly the ~n~ angles having apexes at 57,
58, 59, 60 are larger than those having apexes at 13 or 14
of the prior art example and are bonded to the body of the
cutting tip over a larger proportion of their surface than
are the corresponding extreme elements at points 13 and 14
in the cutting tip shown in Figures 2 and 3. It has been
found that this change in geometry results in stronger
physical structures at the locations of maximum wear due to
chipping in a micro or micro form.
A further strengthening consequence of the
invention derives from the changed angle of attack of
cutting edges 63 and 64 as opposed to that of edges 5 and
7 of Figures 2 and 3.
Arrangements also within the scope of the present
invention are also shown in Figures 9A-9B. In Figure 9A a
tip is provided having a lateral surfaces 70, 71 with flank
edges 72, 73 which have a diameter D3 corresponding to the
diameter of the drill bit. Chamfers 74, 75 at angles F and
G provide the advantages of the present invention by
defining cutting points 76-81 similar to the cutting point
illustrated in Figures 8A, 8B. The chamfered surfaces 74
and 75 respectively form an included angle F or G with the
25 plane of their adjacent flank surface 70 or 71 of from 7.5
degrees to 70 degrees. Preferably, each of the angles F
and G is 45 degrees.
11
l324nl3
Figure 9B illustrates another possible
arrangement within the scope of the present invention where
lateral edges 92, 93 are provided along with a semicircular
flank edges 82, 83 having a diameter D4 equal to the drill
bit diameter and where the edges are chamfered at 84, 85 in
an arc pattern with the length of the chamfer less than the
length of the whole flank edge to define points 86 91.
In general the chamfer surfaces within the scope
of the present invention which define the cutting tip faces
and points can be symmetrical relative to the center of
rotation or they can be nonsymmetrical, they can be the
full length of the flanks or they can extend only for a
part of the
lla
.~
1 3240 1 3
L~
. C ~r~yt~ of the flanks as shown or they can be tilted relative
, to the axis of rotation of tlle drill to produce a triangular
chamfer surface. The chamfers can be 'ncorporated in a
design of the cutting tip wherein the flanks are disposed to
provide clearance relative to the cylindrical surface of
rotation of the drill or in tl,e design of cutting tip
wherein tl,e f1anks coincide with the cylindrica1 surface of
rotatio" of the drill or in t~le design of cutting tip
wherein tl,e flanks are a combination of clearance and
coincidence relative to the surface of rotation of the
drill
Drill bits incorporating features of devices within the
scope of the present invention were tested in comparison
with cutting tips of various prior art configurations but
uniformly without tl,e chamfered leading edges of the flank
surfaces provided by devices within the scope of the present
invention as described hereinbefore. The dril1 bits
incorporating cemented carbide tips having configurations
within the scope of the present invention were compared with
the dril1 bits manufactured by other manufacturers providing
a somewhat similar tip configuration but in no case
providing the additiona1 points as described hereinbefore.
From the testing it WdS conc1uded that as the angle is
increased from 7,5D improvement is noted and that the depth
of the chamfer can be between 1/5 and 3/4 of the de~th of
the tip preferably about l/3.
Tests were cond,lcted with three materials, namely,
pressure c~st concrete with crushed aggregate, concrete with
gravel aggregate anll granite at various feed forces. It
I 1 32401 3
waS found that drill tips in accordance with the present
invention provide superior results illustrated by superior
rate of decrease in penetration rate over that of comparison
drills and the rdte of wear was diminished with the result
that the useful life of the drill was substantially
improved, all as shown in Figure lO which is an illustration
of comparison of the penetration rate of a drill point
referenced to the tota1 depth of drilled holes. The
superiority of devices within the scope of the present
invention is clearly illustrated.
while all of the reasons for the superiority of drill
bits within the scope of the present invention are not fully
understood it is believed that dt least a portion of the
improvement arises because the cutting forces are divided
dmong several points ~hich because of the configuration
are stronger dS previously described. Some improvement also
arises because tl-e cutting edges are oriented to direct the
cutting forces into the body of the tip rather than
tdngentidlly to the arc of the cutting path as is the case
with prior art tips. Furti~er, by redirecting the cutting
forces the strength of the cutting edges are greatly
enhanced. Some improvement may also be achieved because the
overall lengths of the cutting edges are increased reducing
the cutting force per unit length of cutting edge.
l It wil1 be understood tl~dt the foregoing are but a few
examples o~ arrangements within the scope of the present
invention and other drrangements also within the scope of
the present iI~ventioll will occur to those skilled in of the
art upon reading tI,is disclosule set forth hereinbefore.
