Note: Descriptions are shown in the official language in which they were submitted.
~7~33~
This invention relates to a Roof Drill Bit
and more specifically to a drill bit designed partic-
ularly for drilling coal, rock, concrete, mineral ore
and other hard substances.
The nearest state-of-the-art drill bit de-
sign to that of the improved drill bit of this inven-
tion is believed to be that which includes a tubular
head having an out-of-round (hexagonal) recess in one
end to receive a male hexagonal driver and having a
diametrical slot at the other end into which a flat, -
pointed cutting insert, such as ~ungsten carbide i9
secured.~ Quarter segments of the tube at the cutting
; end are removed to provide axial openings to the cen-
ter passage of the tube for fluid flow in connectian
with the removal of chips, particles and dust. This
device has an annular groove inside the driver recess
which is intended~ to cooperate with a retainer device
on a driver insert.
This drill bit above described has disadvan-
ZO tages in that the male driver insert must have a fluid
recess and thus has a wall thickness which is weak and
~- ~ subject to breakage. Also, chips and dust have a tend-
', ~ :
,,
,,:
--1--
1~9~3Z
ency to pile up at the juncture of the bit and the
driver rod. m is causes pile up in the hole being
drilled which causes a binding of the drill bit with
resultant increased strain on the drive juncture.
The present invention contemplates an im-
proved drill bit design which can be used for roof
drilling in mining areas where the roof areas are
to be reinforced by anchor bolting systems, i.e., a
system wherein a mechanical expansion and tensioning
bolt is inserted in a drilled hole, or by resin bolt-
ing wherein a drilled hole is charged with a setting
resin and activated by a core bolt which is inserted
to mix the resin and provide a core for the resin
which sets around it (Mining and Metallurgy, Bulletin
~o. 776, July 1971~. The bit may also be used in
drilling charge holes for blasting, for rock boring,
highway construction, light post base anchor holes,
anchorage railin~s and the like.
The holes used in mining applications are
sometimes quite deep and a dxill driver may have
several sections of drive shafts linked together
before thP hole is complete. It has been customary
to utilize a starter, a driver, a middle extension,
and a finish extension. With the present drill bit
-2-
, , , , , :
1~7332
construction, the starter and the finish extension
can be eliminated, and all that is needed is a driver
and such middle extensions as are required for the
desired depth of the hole.
By utilizing a bit with a male drive exten-
sion cooperating with a female driver element, a
stronger bit unit can be formed with the chip and
dust openings in the bit itself, thus eliminating the
need for side openings in the driver. By reason of
this construction, numerous additional advantageous
features can be incorporated into the bit. The in-
ternal passage on the bit shank can serve as a ven-
turi to increase the flow of fluid. Side and back
clearance can be provided in the bit to prevent the
,
:
~ 15 build-up of dust and chips which will cause resistive
;~ binding and chugging in the drilling operation.
The bit design also lends itself to the use
of a chevron-shaped insert which is self-centering,
,:
, ~.
assuring maximum concentricity, increased brazing
area, and more web strength at the centèr tip sec-
~ .
~: :
tion. An additional feature of the male shank bit
design is the adaptability to a variety of retaining
devices which are positive in action to avoid the
hang-up of the bit in a hole when the driver elements
are re~racted.
,
';~
, -3-
-
.
~g~3Z
It will be appreciated that in the type of
drilling under consideration in rock, coal and other
minerals, there are two systems for removing chips
and dust. One is the suction system wherein a vacuum
pump is connected up to the driving shafts and ulti-
matel~ to the bit so that the removed material is
sucked through the bit and the driving shafts into
a proper receptacle. With this system, the holes in
the bit are usually larger than the other system which
utilizes water under pressureO This water is passed
through the drive shafts and the bit and, in flowing
outwardly around the bit and the shafts, it carries
away the chips and cuttingsO A different extexnal
configuration is util1zed on the suction bit as con- -
trasted with the water pressure bit as will be seen
in the following description.
These and other features of the drill bit
will be evident in the following specification and
claims in which the invention is described together
with the principles of operation and a detailed pre-
sentation of th~ best mode presently contemplated
for the practice of the invention directed to per-
sons skilled in this art to enable them to utilize
the invention.
~7;~3Z
DRAWI~GS accompany the disclosure and the
various views thereof may be briefly described as: -
FIGURE l, a general view of a bit and the
driver mechanism.
FIGURE 2, a side view of a bit blank prior
to machining.
FIGURE 3, a side view of the bit blank 90
turned from the view of FIGURE 2.
FIGURE 4, an end view of the bit blank.
FIGURE 5, a side view of a drilled and ma-
chined blank for use in a suction system.
FIGURE 6, a side view of a drilled and ma-
chined blank 90 turned from the view of FIGURE 5.
FIGURE 7, a sectional view of the drilled
and machined blank.
FIGURE 8, an end view of the machined blank.
FIGURE 9, an assembly view of a finished bit.
FIGURE lO, an end view of the bit assembly.
FIGURE ll, an assembly view of a bit with a
modified cutter insert.
FIGunE 12, a side view of a bit blank modi-
fied for pressure flow chip removal.
FIGURE 13, a side view 90 turned from the
view of FIGURE 12.
--5--
r
~7~3Z
FIGURE 14, a shank end view of the blank o
FIGURES 12 and 13.
FIGURE 15, an end view of the drill bit from
the cutting end.
FIGURE 16, a sectional view of the pressure
flow bit.
FIGURE 17, an assembly view of the pressure
flow bit.
; FIGURE 18~ an end assembly view of the pressure
flow bit.
FIGURE 19, a side view of a pressure flow bit
with a modified chevron type insert.
FIGVRE 20, a view of a retainer device.
WIT~ REFERENCÆ TO THE DRAWINGS, in FIGURE 1,
there is illustrated, in a perspeckive view, a drill-
ing system which includes a drill bit 30, a driver shaft
or tube 32 having a drive coupling 34, and an interme-
diate or middle extension shaft 36~ The bit has a male
drive shank 38, hexagonal in cross-section, which inter-
fits with a female socket end 40 on one end of middle
extension 36. m e other end of extension 36 has a male
shank 42 similar to that on the bit which will in~erfit
with a female socket end 44 on driver 32. It will be
noted that there is a hole 46 in socket 40 which will
--6--
~9~3~:
register with a hole 48 in bit shank 38. A retainer
plug 50, as illustrated in FIGURE 20, formed of a ma-
terial such as Teflon (Trademark)~ to resist heat,
can be driven into the registering holes 46, 48 to
lock the bit to the extension. This plug 50 can be
readily driven from its working location by a drift
pin when the bit is to be removed. A similar reten-
-tion system can be utilized between driver 32 and
extension 36 if desired. Other retainers such as
roll pins and blind rivats may also be utilized. -
-
We turn now to the details of the drill-bIt.
; A bit blank is shown in FIGURES 2 and 3 having an en-
larged head portion 70 on the shank portion 380 This
blank is preferably a steel forging although it may
also be an inves~ment casting or even formed by powder
metallurgy methods. The shank 38 has a hexagonal cross-
section and there is a radius 72 formed at the juncture
~;
, -
: ~ ,
~ 7-
: "
~L~9733~
of the shank with the shoulder 73 of the head having
a minimum radius of 1/16" but preferably in a range
of 3/32" + 1/64", As illustrated in FIGURES 2, 3
and 4, there are segmental cavities 74, 76 formed
axially inward from the outer end o~ the head 70
terminating in a curved sweep 77 to the outside of
the head leaving head stock in the form of prongs
; 78, 80 which extend diametrically over the center
line to form ~rests 82 angled away from the tip cen-
ter.
In FIGURES 5 to 8, the blank 38 in the form
of the original forging is shown after it has been ma-
chined and drilled for use in a suction system of drill-
ing. This machining involved providing the axial open-
ing 84 in the shank 38 which projects up to the headportion 70, and holes 86 are drilled from the bottom
of the segmental cavities 74 and 76 into the axial
recess 84. These holes 86 are about as large as they
can be while leading a reasonable amount of stock on
the outside of the drill body~ All junctions of in-
; ~ ternal holes in the body of the bit, of this embodiment
and that shown ln FIGURES 12 to 19, should have smooth
radii to achieve maximum strength in the part and the
best flow for cuttings in the case of suction type
.
733Z
drills and for water when that is used as the fluid.
Such smooth radii help to avoid build-up of cuttings
in the tool and hence reduce any tendency for it to
plug during operation. To complet.e the machining,
there is a slot 88 milled diametrically across the
cutting end of the body 70 to receive a cutting
blade 90 as illustrated in FIGURES 9 and lO. ~-
The insert 90 is preferably silver brazed
into the slot, the silver brazing alloy lying along
the juncture line 92 where the opposite ends and
sides of the insert 90 are flat against the spaced
prongs 78 and 80 formed when the slot for the insert
is cut through the body 70.
It will be noted that the body 70 retains
its full round circumfexence in ~his embodiment which
: ~ is directed to the suction system. It will be noted
also that the prongs 78 and 80 overlap each other in
~: spaced relation at the center of the tool, as shown in
-~ FIGURES 8 and 10, so that there is a maximum amount of
the prong surfaces in contact with the blade insert,
~: and also a strengthening of the center of the unit by
reason of this overlap and the mass of metal at the
tool tip.
:;
_g_
~97;~3;~ :
The insert support prongs are provided with
a flat secondary clearance angle surface 81 disposed
at about 30 in order to allow easier passage of cut-
tings and less impediment of water flow up and out of
the insert to fully cover the insert and allow easy
return ~low dowrlward along the tool and drive shaft.
The crests 82 of the prongs are also illus-
trated in FIGURES 8 and 10 wherein the prong reaches
a crest at 82 and starts tapering toward the recesses
74 and 76 now containing the holes 86.
This structure results from the overlap of
~ the prongs. The amount of overlap depends on the
; tool size and can be increased proportionately as
the tool diameter increases. This feature increases
the mechanical support for the carbide insert, thus
improving the resistance to chipping and breaking.
This also increases the brazed area on the sides of
the insert which substantially lncreases the strength
of the brazed bond. ~he transverse insert seat of the
insert prongs should have a width approximately the -
same as the thickness or width of the carbide insert
plus the brazing alloy~ This provides maximum strength
in the brazed bond, maximum support to the insert, and
:~ .
--10-
, ~
.
. ., ,, , , , , ~
.. . . . .
10~7:~3Z
minimum impediment to upward or downward flow o~ the
water or cuttings. The flow passageways on either
side of the support prongs are shown parallel to the
axis of the tool to provide maximum flow clearance,
but these passageways might be angled with respect
to the tool axis should there be a reason to direct
the flow in a different direction for some applica-
tion. Thus, the assembled unit with the blade in-
sert brazed in place shown in FIGURES 9 and 10 is
ready for use by inserting the male shan~ 38 into
the female recess in the socket 44 of shaft 32 to
start a hole. Subsequently, if the hole i5 deep
enough, the middle extension 36 can be placed be-
tween the shaft 32 and the bit 30~ The suction source
will be connected, of course, to the coupling 34 as
well as the drive mechanism to obtain the rotary mo-
tion.
In FIGURE 11, a modiied unit is shown in
all respects similar to the previously described em-
bodiment with the exception that the cutting bit in-
sert blade illustrated at 100 has a chevron shape
with a base angle that approximates the outer angle.
The slot then that is cut in the body 70 will also
have this type of base so that the insert 100 will be
self-centering during the brazing operation and also
--11--
~D9~33Z
have an increased resistance to side thrust by reason
of the angled base portions 102. This embodiment pro-
vides somewhat greater contact surface for the brazing
and thus a stronger joint and it facilitates the braz-
ing operation as well as the effectiveness of the unitin operation since it will be centered and prevent out-
of-round holes or greater pressure on one side than the
other due to a variation in side clearance.
This chevron design allows more regrinds and
a truer, more concentric tool. There is, at the same
time, a reduction in the amount of carbide needed for
the insert, yet the life of the tool is not reduced
since the carbide is reduced in the center area where
there is no wear. ~hus, the design provides increased
tool life, reduces wobble during drilling resulting in --
uniform wear characteristics in the tool instead of
wear predominantly on one side as can occur if the
base of the insert is flat and the position during
brazing adjusted visually and manually as is most
often the case. Not only does this design improve the
life of the bit,but the steel drill rods used to drive
the bit will have an lmproved life because o reduced
fatigue stresses resulting from a wobble action.
-12-
~ 97 :~ 3~J
In FIGURES 12 to 19, a modified cutting in-
sert is shown designed especially for the pressure
fluid system of operation which usually includes the
directing of water through the interior of the drive
shafts and the bit to force chips and particles back
along the sides of the hole being drilled. In each
case, the function of the operating fluid is to cool
the cutting bit and reduce dusting as well as to re-
move the debris. Reduction in the dust in a drilling
operation provides improved working conditions in the
drilling area and also reduces the possibility of
fire or explosion. The same blanks that are illus-
trated in FIGURES 2 to 4 are utilized to create the
second embodiment although different forgings which
might reduce the necessary machining could be used.
~ As shown in FIGURE 12, the machining has
; been accomplished to pro~ide the hexagonal drive
shank 38 with the axial opening 84 and the central
body of the unit having a shank end and a cutting
end has been reduced in diameter at the shank end 104
on opposite sides of th~ body to leave the cylindrical
:, :
and circular lands 106 as contact and guide surfaces
while creating side passages for the flow of coolant
fluid. The shank end joins with the cutting end at a
shoulder 107. The segmental pockets in the bit are
drilled at the base to provide the holes 108 connected
;~ to the interior passage 84.
;
:
-13-
3L~397;~32
It will be noted that the holes 108 are
smaller in diameter than those utilized in the embo-
diment of FIGURES 2 to 10, leaving more body stock.
It will be noted also that the axial passage 84 has
a bell mouth flare 110 which is also found in FIG-
URES 2 to 11 for the purpose of creating venturi
effect as the fluid enters the passage 84. This is
most significant in the water system presently being
;~ described. The provision of a slot 112 for receiving
10the cutting insert creates the two prongs 114 and 116
at the cutting end of the bit. ~hese prongs are pref-
erably flattened on the respective sides at 118 to pro-
vide additional fluid~passages for the outflowing water
and enabling a flushing of~the particles back along the
; ~ : :
sides of the hole. This flattening and removal of
stock is shown most clearly in~FIGURES 15~through l9o
The working ends of the prongs are also formed or ma-
chined~ to have a 30 secondary clearance angle as
shown at 81, as previously described in connection
,,; :~ ~ ,
0 with the embodiment of FIGURES 2 to 11, to improve the
flow characteristics of the moving fluid used, in this
. :
~ case, water.
, :
-14-
' ' '
9L~9733Z
In FIGURES 17 and 18, the machined bit is
shown with the blade insert 120 brazed in place. In
each case, the cutting insert has a leading cutting
edge 122 with a relieved portion behind it to create
the necessary cutting action on the sides of the de-
vice. A similar configuration is provided on the
cutting edges which face the bottom of a hole being
: drilled as shown at 124.
In the operation of the water system bit as
illustrated in FI&UXES 12 to 18, the water is directed
through the drill shafts 32 and 36 into th~ axial pass-
age 84 of the drill shank 38 past the ensmalling radius
~:
110 which creates a venturi effect to increase the velo-
city of the fluid as it passes out of the openings 108
to the cutting edges:of the bit and thence rebounds from
~: ~ the bottorn of the hole being drilled to pass outwardly
; of the hole around the clearance areas o the bit and
the driving shaftsO
In FIGURE 19, a bit substantially as shown
in FIGURES 12 to 18, -is provided with a chevron type
: cutting insert 130. This structure would have the
~, :
same advantages as described in connection with the
~ er~bodiment shown in FIGURE 11.
:
~ '
-15-
. ~ .
~733Z
In FIGURE 20, a retainer plug is shown which
could be utilized in connection with the holes 46 in
the drive shafts 32 or 36 and the hole 48 in the shank
38 which would be in registration in assembly. It will
be appreciated that the mouth of the recesses in the
socket ends 40 and 44 o~ shafts 32 and 36 would be flared
to receive the fillet 72 joining the shanks 38 with the
body 70. The retainer plug 50 illustrated in FIGURE 20
is one example of a plug formed with Teflon (Trademark)
which can be driven in to the registering holes to lock
the parts together. As previously indicated, other types
of retainers, such as roll pins and spring clips, would
also be used. In addition to the plug-snap retainer such
as Teflon (Trademark) or any other suitable non-flammable
plastic, a deformable metal may be used such as copper or
aluminum which is soft enough to drive into and through
holes in the steel drill rod and the shank of the bit.
These retainers may be installed and removed with the use
of a punch or by hand~
The change of dimension from the shank 38 to
the head 70, in addition to permitting a drive shaft
with a female socket, provides a stronger drill bit
shank with a venturi central passage especially effec-
tive in the pressure system. However, another advantage
.,~
,,
~97332
derives from this configuration in that a shoulder 73
is formed on the head 70 outside the radius 72. This
shoulder cooperates with the end 41 of socket 40 so
that a thxust surface is developed which assists in
the application of the drilling feed forces. In cases
where the bit is used for rotary percussion drilling,
this is especially important.
It will be appreciated that the male shank
38 can be hexagonal, as shown, in cross-section, rec-
tangular, square, oval, or any other out-of-round
configuration which allows the features of the pre-
sent bit construction to be retained. The preferred
embodiment is hexagonal with square as a second pref-
erence.
The shank and body of the tool bit are pref-
erably formed of forged steel, but any metal may be
used which will have the necessary shock resistance
and strength for the rugged conditions to be met in
the mining field. The cutting insert is preferably
formed of a cemented tungsten carbide having a quality
which adapts it to rock boring or coal mining. There
are many types and grades of carbide which may be
selected for particular applications and other compar-
able cutting metals or powdered metallurgical combina-
-17-
~73~2
, .
tions can be utilized. The cutting inserts are
shown with a sharp corner on the outer facing sur-
faces, but a land may be provided if rotary per-
cussion type drilling is to be done~
While the inserts have been shown as brazed
into the provided slots, mechanical means might be
used to hold them in the head. However, the brazed
inserts are preferred since this provides a rein-
forcement to the entire structure and also enhances
the heat conduction from insert to shank to prevent
undue build-up in the insert itse}f.
:'
`:
.
,
-18-
