Rotatable cutting bit insert

A multi-portion carbide cutting insert which affixes to the forward end of a rotatable cutting bit. The cutting insert has an axially forward tip portion and a flange portion with at least four mediate portions between the tip portion and the flange portion. The first mediate portion has an included angle less than that of the second mediate portion. The second mediate portion has an included angle greater than that of the third mediate portion. The fourth mediate portion has the largest included angle.

BACKGROUND OF THE INVENTION 
The invention pertains to rotatable cutting bits wherein a block on a 
driven body, such as a drum or wheel or blade, rotatably contains the 
cutting bit having a hard cutting insert which affixes to the forward end 
of the cutting bit. More specifically, the invention pertains to the shape 
of the hard cutting insert which affixes to such rotatable cutting bit. 
Rotatable cutting bits are a consumable component of the overall apparatus 
used to break a substrate into a plurality pieces. For example, a road 
planing machine uses rotatable cutting bits which rotatably mount in 
blocks on a driven drum. An engine in the road planing apparatus drives 
the drum. The rotation of the drum causes the cutting bits to impinge upon 
a road surface, such as asphalt. The result is to break the asphalt into 
small pieces thereby preparing the roadway for resurfacing. 
The typical rotatable cutting bit comprises an elongate steel bit body with 
an axially forward end and an axially rearward end. The cutting bit 
contains a means for retaining the bit in the bore of the block such as a 
split sleeve retainer. The block mounts on a rotatable drum driven by the 
road planing machine. A hard cutting insert, typically made from a 
cemented tungsten carbide (WC-Co alloy) having a cobalt content ranging 
from about 5 to about 13 weight percent, affixes to the forward end of the 
cutting bit. Typically, one brazes the hard cutting insert to the steel 
bit body. 
The hard cutting insert is the component of the cutting bit that first 
impinges upon the substrate. Thus, there has been an interest in the shape 
of the hard cutting insert, and the influence the shape of the hard 
cutting insert has on the performance of the cutting bit. 
Because of the importance of conserving resources, it is desirable for a 
hard cutting insert to minimize the volume of cemented tungsten carbide 
necessary to manufacture the same, and thereby conserve tungsten and 
cobalt, without negatively impacting on its performance characteristics. 
One early cutting insert has a conical tip portion which joins to a 
cylindrical portion. The cylindrical portion mounts in a cylindrical bore 
at the axially forward end of the steel bit body. U.S. Pat. No. 3,830,546 
to Kniff shows one example of such a hard cutting insert. 
Another early cutting insert has coaxial and integral portions comprising a 
conical tip portion, a frusto-conical mediate portion which is axially 
rearward of the tip portion, a flange portion which is axially rearward of 
the mediate portion and a portion which mounts in a socket in the axially 
forward end of the steel bit body. One example of this style of cutting 
insert is found in German Offenlengungsshrift No 2846744. Another example 
of this basic style of cutting insert is the model C-1445-7 by 
Multi-Metals, a business unit of Vermont American, of Louisville, Ky., 
wherein there is small fillet and/or a manufacturing flat, between the 
cylindrical base portion and the frusto-conical inter-mediate portion. 
Another example of a cutting insert similar to the Multi-Metals insert, at 
least to the extent that there is a fillet between the frusto-conical 
section and the base section, is the T-104-76 cutting insert made by 
American Mine Tool, a division of GTE Valenite Corporation, having 
facilities in Bristol, Va. and Madisonville, Ky. 
Another early style of cutting insert has a conical tip portion, a 
frusto-conical portion axially rearward of the tip portion, an arcuate 
portion axially rearward of the frusto-conical portion, a flange portion 
axially rearward of the arcuate portion, and a valve seat portion axially 
rearward of the flange portion. The cutting insert mounts at the valve 
seat portion into a corresponding socket in the forward end of the steel 
bit body. One example of this style of cutting insert is the Kennametal 
tip style 921-01135 found at one time in Kennametal C-3MLR cutting bits. 
Another early style of cutting insert has a conical tip section, a 
frusto-conical section axially rearward of the tip section, an arcuate 
section axially rearward of the mediate section, and a cylindrical base 
section axially rearward of the mediate section. The cutting insert mounts 
via the base section into a socket in the forward end of the steel bit 
body. One example of this style of cutting insert is the T-104-13 cutting 
insert used in the AM722RF construction tool sold by American Mine Tool. 
General speaking, this cutting insert is the subject matter of U.S. Pat. 
No. 4,497,520 to Ojanen. 
Another early cutting insert has a shape along the lines of the T-104-13 
cutting insert, but further includes a small cylindrical section between 
the tip section and the frusto-conical section. One example of this style 
of cutting insert is the T-104-14 cutting insert as used in the AM722RF 
construction tool sold by American Mine Tool. Generally speaking, this 
insert is the subject matter of U.S. Pat. Nos. 4,725,099 and 4,865,392 to 
Penkunas et al. 
Another early cutting insert has a conical tip section, a cylindrical 
section axially rearward of the tip portion, an arcuate section axially 
rearward of the cylindrical portion, a flange section axially rearward of 
the arcuate portion and a section by which the cutting insert mounts in a 
socket in the steel bit body. One example of this cutting insert is shown 
by U.S. Pat. No. 4,938,538 to Larsson et al. and European Patent No. 0 122 
893 to Larsson et al. 
Another example of an earlier cutting insert has a conical tip portion, a 
single arcuate mediate portion axially rearward of the tip portion, a 
flange portion axially rearward of the arcuate portion, and a valve seat 
portion axially rearward of the flange portion. The valve seat portion 
mounts in a socket found in the forward end of the steel bit body. 
Kennametal Drawing Nos. 921-01171 and 921-01173 each show this style of 
cutting insert which was at one time used in some Kennametal construction 
tools. 
U.S. Pat. Nos. 4,911,503 and 4,911,504 to Stiffler et al., assigned to the 
assignee of the present application, show a cutting insert with a conical 
tip portion and a cylindrical flange portion which join together via a 
bell-shaped intermediate portion. Three concave surfaces, each of a 
different radius, blend together to form the bell-shaped surface. 
Soviet Author's Certificate No 899,916 shows a hard carbide tip which 
mounts in a steel body. The hard insert has a conical tip section, a 
cylindrical mediate section integral with and axially rearward of the tip 
section. A large diameter cylindrical flange section is integral with and 
axially rearward of the mediate section. A radius joins the mediate 
section with the flange section. A second cylindrical section is integral 
with and axially rearward of the large diameter flange portion. A bore in 
the steel body receives the second cylindrical section so as to mount the 
carbide tip to the steel body. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved rotatable cutting 
bit with a hard cutting insert. 
It is another object of the invention to provide an improved cutting bit 
wherein the shape of the cutting insert contributes to the improved 
performance of the cutting bit. 
It is still another object of the invention to provide an improved cutting 
bit wherein the shape of the cutting insert helps conserve tungsten and 
cobalt, which are valuable resources. 
In one form thereof, the invention is a cutting insert made from a hard 
material wherein the insert comprises an axially forward tip portion of a 
general conical shape, a first mediate portion integral with and axially 
rearward of the tip portion, a second mediate portion integral with and 
axially rearward of the first mediate portion, a third mediate portion 
integral with and axially rearward of the second mediate portion, a fourth 
mediate portion integral with and axially rearward of the third mediate 
portion, and a flange portion integral with and axially rearward of the 
fourth mediate portion. 
Preferably, the first mediate portion has a transverse dimension at its 
joinder with the tip portion that is less than or equal to the transverse 
dimension at its joinder with the second mediate portion. The second 
mediate portion has a lesser transverse dimension at its joinder with the 
first mediate portion than at its joinder with the third mediate portion. 
The third mediate portion has a transverse dimension at its joinder with 
the second mediate portion that is less than or equal to the transverse 
dimension with its joinder with the fourth mediate portion. The fourth 
mediate portion has a lesser transverse dimension at its joinder with the 
third mediate portion than at its joinder with the flange portion. The 
flange portion is of a generally cylindrical shape. 
In another form thereof, the invention is a rotatable construction bit 
comprising an elongate bit body with opposite forward and rearward ends. A 
cutting insert of a hard material is affixed to the bit body at the 
forward end thereof. 
The cutting insert includes an axially forward tip portion of a general 
conical shape. The cutting insert further includes a first mediate portion 
integral with and axially rearward of the tip portion, and having a first 
included angle of taper greater than or equal to 0.degree.. A second 
frusto-conical portion is integral with and axially rearward of the first 
mediate portion, and has a second included angle of taper. The second 
included angle of taper is greater than the first included angle of taper. 
The cutting insert also includes a third mediate portion that is integral 
with and axially rearward of the second mediate portion. The third mediate 
portion has a third included angle of taper greater than or equal to 
0.degree.. The third angle of taper is less than the second included angle 
of taper. The cutting insert also includes a fourth frusto-conical portion 
that is integral with and axially rearward of the third mediate portion. 
The fourth frusto-conical portion has a fourth included angle of taper. 
The cutting insert further includes a flange portion integral with and 
axially rearward of the fourth frusto-conical portion. The flange is of a 
generally cylindrical shape. 
These and other aspects of the present invention will become more apparent 
upon review of the drawings, which are briefly described below in 
conjunction with the detailed description of specific embodiments of the 
invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
Referring to FIG. 1, wherein FIG. 1 illustrates one specific embodiment of 
the rotatable cutting bit 10 of the present invention. Cutting bit 10 
comprises three basic components; namely, an elongate steel body 12, a 
retainer sleeve 14 such as described in U.S. Pat. No. 4,201,421 to Den 
Besten et al., and a hard cutting insert 16. 
The material for the hard cutting insert is typically a cemented tungsten 
carbide which is an alloy of tungsten carbide and cobalt. The cemented 
carbide tip may be composed of anyone of the standard tungsten 
carbide-cobalt compositions conventionally used for construction 
applications. The specific grade of cemented carbide depends upon the 
particular application to which one puts the tool. The cobalt content 
ranges from about 5 to about 13 weight percent with the balance being 
tungsten carbide, except for impurities. For rotatable cutting tools used 
in road planing, it may be desirable to use a standard tungsten carbide 
grade containing between about 5.4 to about 6.0 weight percent cobalt 
(balance WC) and having a Rockwell A hardness between about 88.2 and about 
88.8. 
The steel bit body 12 has an axially forward end 18 and an axially rearward 
end 20. The forward end 18 preferably contains a socket 22 therein, and it 
is at this location that the hard cutting insert 16 affixes to the bit 
body 12. 
In regard to all of the specific embodiments, it is preferred that a high 
temperature braze material be used in joining the cemented carbide insert 
to the steel body so that braze joint strength is maintained over a wide 
temperature range. The preferred braze material is a HIGH TEMP 080 
manufactured and sold by Handy & Harman, Inc., 859 Third Avenue, New York, 
N.Y. 10022. The nominal composition (weight percent) and the physical 
properties of the Handy & Harman HIGH TEMP 080 braze alloy (according to 
the pertinent product literature from Handy & Harman, U.S. Pat. No. 
4,631,171 covers the HIGH TEMP 080 braze alloy) are set forth below: 
______________________________________ 
NOMINAL Copper 54.85% .+-.1.0 
COMPOSITION Zinc 25.0 .+-.2.0 
Nickel 8.0 .+-.0.5 
Manganese 12.0 .+-.0.5 
Silicon 0.15 .+-.0.5 
Other Elements 0.15 
PHYSICAL Color Light Yellow 
PROPERTIES: Solidus 1575.degree. F. (855.degree. C.) 
Liquidus (Flow Point) 
1675.degree. F. (915.degree. C.) 
Specific Gravity 
8.03 
Density (lbs/cu. in.) 
.290 
Electrical Conductivity 
6.0 
(% I.A.C.S.) 
Electrical Resistivity 
28.6 
(Microhm-cm.) 
Recommend Brazing 
1675-1875.degree. F. 
Temperature Range 
(915-1025.degree. C.) 
______________________________________ 
Another braze alloy which applicants consider to be acceptable is the HANDY 
HI-TEMP 548 braze alloy. HANDY HI-TEMP 548 alloy is composed of 55.+-.1.0 
w/o (weight percent) Cu, 6.+-.0.5 w/o Ni, 4.+-.0.5 w/o Mn, 0.15.+-.0.05 
w/o Si, with the balance zinc and 0.50 w/o maximum total impurities. 
Further, information on HANDY HI-TEMP 548 can be found in Handy & Harmon 
Technical Data Sheet No. D-74 available from Handy & Harmon, Inc. 
The bit body 12 has a reduced diameter section 24 near the rearward end 20 
thereof. The enlarged diameter portions 26, 28, which define the ends of 
the reduced diameter portion 24, maintain the retainer sleeve 14 captive 
on the bit body 12. Because the reduced diameter portion 24 is of a 
diameter smaller than the inside diameter of the retainer sleeve 14, the 
retainer sleeve 14 is free to rotate relative to the bit body 12. 
The bit body 12 mounts in the bore 30 of a block 32 which affixes to a 
driven member (not illustrated) such as a drum of a road planing machine. 
Once the bit 10 is within the volume of bore 30, the retainer sleeve 14 is 
resiliently compressed radially inwardly and thereby frictionally engages 
the wall of the bore 30. The bit 10 mounts to the block 32 in such a 
fashion so the it is free to rotate within the bore 30 relative to the 
block 32. 
Referring to FIGS. 2-4 the hard cutting insert 16 includes a plurality of 
integral portions in coaxial alignment. These portions include a tip 
portion 40 which is of a generally conical shape. The tip portion 40 
terminates at its axially forward end in a semi-spherical portion 42. The 
radius "x" of the semi-spherical portion 42 is equal to about 0.06 inches. 
Tip portion 40 increases in transverse diameter in a direction axially 
rearwardly from the termination point. In the specific embodiment, tip 
portion 40 has an axial length "a" of about 0.130 inches, a maximum 
diameter "b" of about 0.310 inches, and an included angle "c" of about 
90.degree.. 
The hard cutting insert 16 further includes a first mediate portion 44, 
which is integral with the tip portion 40. The first mediate portion 44 is 
axially rearward of the tip portion 40. First mediate portion 44 increases 
in transverse dimension in a direction axially rearwardly from the joinder 
with the tip portion 40. In the specific embodiment, the shape of the 
surface of the first mediate portion is generally frusto-conical. First 
mediate portion 44 has an axial length "d" of about 0.109 inches. First 
mediate portion 44 has a maximum diameter "f" of about 0.329 inches. The 
minimum diameter of the first mediate portion 44 is equal to the maximum 
diameter b of the tip portion 40. First mediate portion 44 has an included 
angle "g" of about 10.degree.. 
The hard cutting insert 16 further includes a second mediate portion 46, 
which is integral with the first mediate portion 44. The second mediate 
portion 46 increases in transverse dimension in a direction axially 
rearwardly from the joinder with the first mediate portion 44. In the 
specific embodiment, the shape of the second mediate portion 46 is 
generally frusto-conical. Second mediate portion 46 has an axial length 
"h" of about 0.113 inches. Second mediate portion 46 has a maximum 
diameter "j" of about 0.407 inches. The minimum diameter of the second 
mediate portion 46 is equal to the maximum diameter f of the first mediate 
portion 44. Second mediate portion 46 has an included angle "k" of about 
30.degree.. 
The hard cutting insert 16 further includes a third mediate portion 50, 
which is integral with the second mediate portion 46. The third mediate 
portion 50 is axially rearward of the second mediate portion 46. In this 
specific embodiment, the third mediate portion 50 increases in transverse 
dimension in a direction axially rearwardly from the joinder with the 
second mediate portion 46. In the specific embodiment, the shape of the 
surface of the third mediate portion 50 is generally frusto-conical. Third 
mediate portion 50 has an axial length "l" of about 0.109 inches. Third 
mediate portion 50 has a maximum diameter "n" of about 0.447 inches. The 
minimum diameter of the third mediate portion 50 is equal to the maximum 
diameter j of the second mediate portion 46. Third mediate portion 50 has 
an included angle "o" of about 21.degree.. 
The cutting insert 16 further includes a fourth mediate portion 54, which 
is integral With the third mediate portion 50. The fourth mediate portion 
54 increases in transverse dimension in a direction axially rearwardly 
from the joinder with the third mediate portion 50. In the specific 
embodiment, the shape of the fourth mediate portion 54 is generally 
frusto-conical. Fourth mediate portion 54 has an axial length "p" of about 
0.173 inches. Fourth mediate portion 54 has a maximum diameter "r" of 
about 0.625 inches. The minimum diameter of the fourth mediate portion 54 
is equal to the maximum diameter of the third mediate portion 50. Fourth 
mediate portion 56 has an included angle "s" of about 78.degree.. 
The cutting insert 16 further includes a flange portion 60 which is of a 
generally cylindrical shape. Flange portion 60 is integral with and 
axially rearward of fourth mediate portion 54. The axial length "t" of 
flange portion 60 is equal to about 0.070 inches. The diameter of the 
flange portion 60 is equal to the maximum diameter r of the fourth mediate 
portion 54. 
The cutting insert 16 also includes a valve seat portion 62. Valve seat 
portion 62 has an axially forward frusto-conical portion 64 which is 
integral with an axially rearward frusto-conical portion 66. Axially 
rearward frusto-conical portion 66 terminates in a flat surface 68. The 
axial length "u" of the valve seat portion 62 is about 0.154 inches. 
The surface of the axially forward frusto-conical section 64 presents a 
trio of circumferentially equi-spaced bumps 70. These bumps 70 provide for 
the correct centering of the hard cutting insert 16 in the socket 22 and 
for a substantially uniform thickness of the braze joint therebetween. In 
this regard, the cutting insert affixes into the socket via brazing by 
known techniques whereby there is a braze joint between the surface of the 
axially forward frusto-conical section 64 and the corresponding surface of 
the socket. U.S. Pat. No. 4,981,328 to Stiffler et al., assigned to the 
assignee of the present application, describes the function and advantages 
of the bumps 70 in more detail. 
Referring to FIGS. 5 and 6, the second specific embodiment of the hard 
cutting insert 76 includes a plurality of integral portions in coaxial 
alignment. These portions include a tip portion 78 which is of a generally 
conical shape. The tip portion 78 terminates at its axially forward end in 
a semi-spherical portion 80. The radius "xx" of the semi-spherical portion 
80 is equal to about 0.125 inches. Tip portion 78 increases in transverse 
diameter in a direction axially rearwardly from the termination point. In 
the specific embodiment, the shape of the surface of the tip portion 78 is 
generally conical. Tip portion 78 has an axial length "aa" of about 0.193 
inches, a maximum diameter "bb" of about 0.440 inches, and an included 
angle "cc" of about 80.degree.. 
The cutting insert 76 further includes a first mediate portion 82, which is 
integral with the tip portion 78. The first mediate portion 82 is axially 
rearward of the tip portion 78. First mediate portion 82 is of cylindrical 
shape. First mediate portion 82 has an axial length "dd" of about 0.115 
inches. The diameter of the first mediate portion 82 is equal to the 
maximum diameter of the tip portion 78. 
The hard cutting insert 76 further includes a second mediate portion 84, 
which is integral with the first mediate portion 82. The second mediate 
portion 84 increases in transverse dimension in a direction axially 
rearwardly from the joinder with the first mediate portion 82. In the 
specific embodiment, the shape of the second mediate portion 84 is 
generally frusto-conical. Second mediate portion 84 has an axial length 
"hh" of about 0.116 inches. Second mediate portion 84 has a maximum 
diameter "jj" of about 0.515 inches. The minimum diameter of the second 
mediate portion 84 is equal to the diameter of the first mediate portion 
82. Second mediate portion 84 has an included angle "kk" of about 
36.degree.. 
The hard cutting insert 76 further includes a third mediate portion 88, 
which is integral with the second mediate portion 84. The third mediate 
portion 88 is axially rearward of the second mediate portion 84. In this 
specific embodiment, the third mediate portion 88 increases in transverse 
dimension in a direction axially rearwardly from the joinder with the 
second mediate portion 84. In the specific embodiment, the shape of the 
surface of the third mediate portion 84 is generally frusto-conical. Third 
mediate portion 84 has an axial length "ll" of about 0.111 inches. Third 
mediate portion 84 has a maximum diameter "nn" of about 0.578 inches. The 
minimum diameter of the third mediate portion 88 is equal to the maximum 
diameter of the second mediate portion. Third mediate portion 84 has an 
included angle "oo" of about 32.degree.. 
The hard cutting insert 76 further includes a fourth mediate portion 90, 
which is integral with the third mediate portion 88. The fourth mediate 
portion 90 increases in transverse dimension in a direction axially 
rearwardly from the joinder with the third mediate portion 88. In the 
specific embodiment, the shape of the fourth mediate portion 90 is 
generally frusto-conical. Fourth mediate portion 90 has an axial length 
"pp" of about 0.089 inches. Fourth mediate portion 90 has a maximum 
diameter "rr" of about 0.750 inches. The minimum diameter of the fourth 
mediate portion is equal to the maximum diameter of the third mediate 
portion. Fourth mediate portion 90 has an included angle "ss" of about 
88.degree.. 
The hard cutting insert 76 further includes a flange portion 92 which is of 
a generally cylindrical shape. Flange portion 92 is integral with and 
axially rearward of fourth mediate portion 90. The axial length "tt" of 
flange portion 92 is about 0.070 inches. 
The hard cutting insert 76 also includes a valve seat portion 94. Valve 
seat portion 94 has an axially forward frusto-conical portion 96 which is 
integral with an axially rearward frusto-conical portion 98. Axially 
rearward frusto-conical portion 98 terminates in a flat surface 100. The 
axial length "uu" of the valve seat portion 94 is about 0.188 inches. 
The surface of the axially forward frusto-conical portion 96 presents a 
trio of circumferentially equi-spaced bumps 102. These bumps 102 provide 
for the correct centering of the hard cutting insert 76 in the socket 22 
and for a substantially uniform thickness of the braze joint. In this 
regard, the cutting insert 76 affixes into the socket 22 via brazing 
whereby there is a braze joint between the surface of the axially forward 
frusto-conical section and the corresponding surface of the socket. U.S. 
Pat. No. 4,981,328 to Stiffler et al. describes the function of bumps like 
bumps 102 in more detail. 
Referring to FIGS. 7 and 8, a third specific embodiment of the hard cutting 
insert 76' is shown by these drawings. The third specific embodiment of 
the hard cutting insert 76' includes a plurality of integral portions in 
coaxial alignment. These portions include a tip portion 78' which is of a 
generally conical shape. The tip portion 78' terminates at its axially 
forward end in a semi-spherical portion 80'. The radius "xxx" of the 
semi-spherical portion 80' is equal to about 0.125 inches. Tip portion 78' 
increases in transverse diameter in a direction axially rearwardly from 
the termination point. In the specific embodiment, the shape of the 
surface of the tip portion 78' is generally conical. Tip portion 78 has an 
axial length "aaa" of about 0.160 inches, a maximum diameter "bbb" of 
about 0.385 inches, and an included angle "ccc" of about 80.degree.. 
The cutting insert 76' further includes a first mediate portion 82', which 
is integral with the tip portion 78'. The first mediate portion 82' is 
axially rearward of the tip portion 78'. First mediate portion 82' is of 
cylindrical shape. First mediate portion 82' has an axial length "ddd" of 
about 0.116 inches. The diameter of the first mediate portion 82' is equal 
to the maximum diameter of the tip portion 78'. 
The hard cutting insert 76' further includes a second mediate portion 84', 
which is integral with the first mediate portion 82'. The second mediate 
portion 84' increases in transverse dimension in a direction axially 
rearwardly from the joinder with the first mediate portion 82'. In the 
specific embodiment, the shape of the second mediate portion 84' is 
generally frusto-conical. Second mediate portion 84 has an axial length 
"hhh" of about 0.115 inches. Second mediate portion 84' has a maximum 
diameter "jjj" of about 0.460 inches. The minimum diameter of the second 
mediate portion 84' is equal to the diameter of the first mediate portion 
82'. Second mediate portion 84' has an included angle "kkk" of about 
36.degree.. 
The hard cutting insert 76' further includes a third mediate portion 88', 
which is integral with the second mediate portion 84'. The third mediate 
portion 88' is axially rearward of the second mediate portion 84'. In this 
specific embodiment, the third mediate portion 88' increases in transverse 
dimension in a direction axially rearwardly from the joinder with the 
second mediate portion 84'. In the specific embodiment, the shape of the 
surface of the third mediate portion 88' is generally frusto-conical. 
Third mediate portion 88' has an axial length "lll" of about 0.116 inches. 
Third mediate portion 88' has a maximum diameter "nnn" of about 0.527 
inches. The minimum diameter of the third mediate portion 88' is equal to 
the maximum diameter of the second mediate portion. Third mediate portion 
84' has an included angle "ooo" of about 32.degree.. 
The hard cutting insert 76' further includes a fourth mediate portion 90', 
which is integral with the third mediate portion 88'. The fourth mediate 
portion 90' increases in transverse dimension in a direction axially 
rearwardly from the joinder with the third mediate portion 88'. In the 
specific embodiment, the shape of the fourth mediate portion 90' is 
generally frusto-conical. Fourth mediate portion 90' has an axial length 
"ppp" of about 0.116 inches. Fourth mediate portion 90' has a maximum 
diameter "rrr" of about 0.750 inches. The minimum diameter of the fourth 
mediate portion is equal to the maximum diameter of the third mediate 
portion. Fourth mediate portion 90' has an included angle "sss" of about 
88.degree.. 
The hard cutting insert 76' includes an axially rearward cylindrical 
portion 108 that is integral with and axially rearward of the fourth 
mediate portion 90'. The axial length "ttt" of cylindrical portion 108 is 
equal to about 0.070 inches. Cylindrical portion 108 has a bottom surface 
110. A recess 112 is in the bottom surface 110 of the hard cutting insert 
76'. 
Recess 112 has a configuration which receives a protrusion 114 at the 
axially forward end 18' of the steel body 12'. The hard cutting insert 76' 
mounts to the protrusion 114 via brazing. U.S. Pat. Nos. 4,911,503 and 
4,911,504 to Stiffler et al. describe in more detail the attachment of a 
hard cutting insert with a recess to a bit body with a protrusion. These 
descriptions are incorporated by reference herein. 
Although the third mediate portion in each of the three specific 
embodiments is of a frusto-conical shape, it is within the scope of the 
invention for the third mediate portion to be of a generally cylindrical 
shape. 
In regard to the manufacture of the hard cutting insert, all three specific 
embodiments of the hard cutting insert are made in essentially the same 
way. For exemplary purposes, the written description describes the 
manufacture of hard cutting insert 76. 
One makes the hard cutting insert 76 through powder metallurgical 
techniques wherein loose powders of tungsten carbide cobalt, and a 
pressing lubricant are in a die cavity. The punch-die arrangement then 
presses the loose powder into a selected configuration which those skilled 
in the art call a green compact. The green compact undergoes sintering to 
remove the lubricant and consolidate the tungsten carbide and cobalt to 
form the as-sintered part which comprises a dense tungsten carbide-cobalt 
alloy of a particular shape. 
Referring to the manufacture of the second specific embodiment of the hard 
insert 76, FIG. 9A shows the die case 120 which has a top end 122 and a 
bottom end 124 which is opposite from the top end 122. The die case 120 
includes a central die cavity which has a cylindrical configuration 126 
near the top end 122. The die cavity further includes three frusto-conical 
configurations 128, 130, and 132 which correspond to form the fourth 
mediate portion 90, the third mediate portion 88 and the second mediate 
portion 84 of the hard cutting insert 76, respectively. A cylindrical 
configuration 134 is below the frusto-conical configurations, and forms 
the cylindrical portion 82 of the hard cutting insert 76. 
The top punch 136 includes a recess therein which has two frusto-conical 
configurations 138 and 140 which form the frusto-conical portions 98 and 
96, respectively, of the valve seat 94. The bottom punch 142 has a conical 
recess 144 which forms the conical tip portion 78 of the cutting insert 
76. The outside edge of the lower punch 142 includes a small manufacturing 
flat 146 so that the punch does not terminate in a feather edge. The same 
is true for the upper punch 136 which has a manufacturing flat 148 at the 
outside edge thereof. 
To form a green compact of the cutting insert, loose powder of tungsten 
carbide, cobalt and a pressing lubricant is deposited within the die 
cavity. At this point in the process, the punches 136 and 142 are apart as 
shown in FIG. 9A. Once the correct volume of loose powder is within the 
die cavity, the punches move toward each other so as to press the loose 
powder into a green compact. FIG. 9B shows the point at which the punches 
form the green compact. Because of the fact that the punches move toward 
each other to compact the loose powder, the green compact achieves a 
relatively uniform density. The existence of a green compact of a 
relatively uniform density facilitates the reduction of cracks in the 
as-sintered hard cutting insert, which is a highly desirable result. 
In operation, the cutting bit 10 rotates about its central longitudinal 
axis while the drum rotates to drive the cutting bit 12 into a substrate 
such as an asphalt road surface. The longitudinal axis of the drum is 
transverse to the longitudinal axis of the cutting bit. The hard cutting 
insert (16, 76, 76') is the component of the cutting bit 10 which actually 
first impinges upon the substrate. Applicants now provide a description of 
the operation of the specific embodiments of the hard cutting inserts 
below. 
Referring to the first specific embodiment of the hard cutting insert 16, 
the tip portion 40 first impinges upon the substrate. As the cutting bit 
drives further into the substrate, the first mediate portion 44, the 
second mediate portion 46, the third mediate portion 50, the fourth 
mediate portion 54 and the flange 60 each interact with the substrate or 
pieces thereof. 
As the hard cutting insert 16 of each cutting bit continues to impact the 
substrate upon each rotation of the drum, the cutting insert 16 
experiences wear. The nature of the wear is such that the tip portion 40 
will wear away so that the part of the hard cutting insert 16 which first 
impacts the substrate becomes the first mediate portion 44. The first 
mediate portion 44 has an included angle g equal to about 10.degree.. The 
second mediate portion 46 increases in its transverse dimension at an 
angle k of 30.degree.. This angle is greater than the included angle g, 
and therefore, provides a continual increase in the volume of carbide 
which functions to strengthen and support the first mediate portion 44 
during the cutting operation. 
Once the first mediate portion wears away, the second mediate portion first 
impinges upon the substrate. 
Once the second mediate portion has worn away and the third mediate portion 
first impinges the substrate. 
The fourth mediate portion 54 increases at an angle s equal to about 
78.degree., which is significantly greater than angle o of the third 
mediate portion. The fourth mediate portion 54 functions to support and 
strengthen the third mediate portion 52. At the point in time where the 
hard cutting insert 16 wears down to the fourth mediate portion 54, the 
cutting insert reaches a point where its effectiveness is substantially 
reduced. 
Referring now to FIGS. 5 and 6, in the operation of the second specific 
embodiment of the hard cutting insert 76, the tip portion 78 first 
impinges upon the substrate. As the cutting bit 10 drives further into the 
substrate, the first mediate portion 82, the second mediate portion 84, 
the third mediate portion 88, the fourth mediate portion 90 and the flange 
92 each interact with the substrate or pieces thereof. 
As the hard cutting insert 76 of each cutting bit continues to impact the 
substrate upon each rotation of the drum, the cutting insert 76 
experiences wear. The nature of the wear is such that the tip portion 78 
will wear away so that the part of the hard cutting insert 76 which first 
impacts the substrate becomes the first mediate portion 82. 
The first mediate portion 82 has a cylindrical shape. The second mediate 
portion 84 increases in its transverse dimension at an angle kk of 
36.degree.. This angle provides a continual increase in the volume of 
carbide. This continual increase in carbide functions to support and 
strengthen the first mediate portion during the cutting operation. 
Once the first mediate portion wears away, the second mediate portion first 
impinges upon the substrate. 
Once the second mediate portion has worn away, the third mediate portion 
first impinges upon the substrate. The third mediate portion 88 increases 
in its transverse dimension at an angle oo equal to 32.degree., which is 
less than included angle kk (36.degree.). 
The fourth mediate portion 90 increases at an angle ss, which is about 
88.degree., which is significantly greater than angle oo (32.degree.) of 
the third mediate portion. The fourth mediate portion 90 functions to 
support and strengthen the third mediate portion 88. At the point in time 
where the hard cutting insert 76 wears down to the fourth mediate portion 
90, the cutting insert reaches a point where its effectiveness is 
substantially reduced. 
The operation of the third specific embodiment is essentially the same as 
that of the second specific embodiment. Thus, a description of the third 
specific embodiment is not set forth herein since the description of the 
operation of the second specific embodiment will suffice for that of the 
third specific embodiment. 
It can be seen that the present invention presents a rotatable cutting bit 
with a cutting insert that provides certain advantages. 
The second mediate portion has an included angle greater than that of the 
first mediate portion, and thus, provides support and strength for the 
first mediate portion. 
The fourth mediate portion has the largest included angle and provides 
support and strength for the third mediate portion, as well as the entire 
cutting insert during its operation. 
Each one of the specific embodiments of the hard cutting insert presents a 
shape that conserves the volume of cemented tungsten carbide necessary to 
make the hard cutting insert. Thus, this invention helps conserve the 
valuable resources of tungsten and cobalt. 
In each one of the specific embodiments, the tip portion is axially forward 
of and has a larger included angle than that of the first mediate portion. 
During operation, the tip portion with the larger included angle functions 
to help divert, and direct to some extent, debris away from the surface of 
the first mediate portion. By directing such debris away from the first 
mediate portion, the integrity of the first mediate portion is better 
maintained than in the absence of such diversion. 
In each specific embodiment, the second mediate portion is axially forward 
of and has a larger included angle than that of the third mediate portion. 
During operation, the second mediate portion with the larger included 
angle functions to help divert, and direct to some extent, debris away 
from the surface of the third mediate portion. By directing such debris 
away from the third mediate portion, the integrity of the third mediate 
portion is better maintained than in the absence of such diversion. 
As is well known to those of ordinary skill in the art, at the junctures of 
the various surfaces described on the carbide tip, rounds, chamfers, 
fillets and/or pressing flats may be provided, where appropriate, to 
assist in manufacturing and/or provide added strength to the structure. 
Other specific embodiments of the invention will be apparent to those 
skilled in the art from a consideration of this specification or practice 
of the invention disclosed herein. It is intended that the specification 
and specific embodiments be considered as exemplary only, with the true 
scope and spirit of the invention being indicated by the following claims.