Note: Descriptions are shown in the official language in which they were submitted.
This in~ention relates to cutter bits, and more
particularly to a cutter bit assembly of the type having a
cutter bit holder~
This is a division of copending Canadian Patent
Application Serial No. 336,238, filed September 24, 1979.
In mining operation a driven element or bit is used to
dislodge the bedded material such as for example coal. Because
of the ~orces on the bit and the abrasiveness of its contact
with the material, bits are subject to high wear and must be
replaced at periodic intervals in the mining operation. It is
therefore desirable to have a means for attaching the bit to the
mining equipment that is secure and whlch allows for easy
bit replacement. One solution has been to'have a two piece
means for attaching the bit, a base piece and a holder piece.
A base piece is securely attached to the mining apparatus,
! such as for example by w~lding such a base piece to the rotating
drum of a continuous miner. Such a base piece may have a
socket therein adapted to receive a holder piece. The holder
piece is adapted to receive the bit and to be readily replaceable
in the base piece as this holder piece is also subject to wear
during normal operation. Such a system of bit, holder, and base
allow each,component to be replaced independently and with an
ease of replacement generally proportionate to its expected life.
In the past two approaches to solving the problems
of durability and replaceability in cutter bit
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atta~hment have been developed. The first approach has
been to use large steel mounting blocks and heavy lug
type ~it holders. The heavy lug ifi either pinned or
bolted to the block to secure the two portions. While
this type of lu~ and block a~rangement solve some of
the problems inherent in bit attachment f the basic ap-
proach is strength through sheer physical size~ This
solution naturally results in a large block and lug with
corresponding high manufactur~ng costs and unnecessary
weight. Since this approach has placed paramount emphasis
on siæe to resist the primary cutting forces it has not
addressed itself to the problem of movement between the
lug and mounting block. Such vement between a bit
holder and a mounting base can cause unnecessary wear
.
life of the holder and mounting base. ~his wear results
in shortened ~ife of the mounting base and the mining
machine driving component, such as for example the cutting
drum on a continuous miner. U.S. Reissue patent 28,310
and U.S. patent 3,697,137 are representative of this
large lug and ~lock approach to the pro~lemD
An alternative approach to the problem has
been to use a mounting base or block having a central
- socket. A bit holder having a shank portion is inserted
into the socket and clamped in place. This socket type
approach generally results in a smaller more efficient
mab/;~
~L19L73~S~
., .
bit holder and base assembly. U.S. Patent 3,498,~77 and
3,992,061 are indicative of this approach. Such socket type
designs have concentrated on supporting the bit and bit holder
to resist the primary cutting forces b~ urging the shank
poxtion of the bit holder reaxwaxd and downwaxd in the socket.
By use of the holdex shank and efficiently design suppoxt
surfaces on the bit holdex this approach has resulted in a
smaller assembly that adequately resiststhe primary cutting
forces. The small size of the socket t~pe bit holder creates
another consideration ln that the moment arm fxom the load
beaxing surfaces to the axis of the shank has been reduced.
This reduction in moment arm lessens the effectiveness of the
holaex and base combination to resist rotation of the holder
about the axis of the shank. Rotational toxques about the
shank axis result in unnecessary weax to both the h~lder
and the bito This invention pxovides for resistlng these
rotational tor~ues and retarding rotational movement of the
holder about the centraI axis of the socket.
Because the base should have a long life~ it is
~0 usually welded to the mining machiner drum, or chain; and this
securing attachment represents little real pxoblems. This
invention xelates to the attachments of the bit to the holder,
and the holdex to the base. One
,
.
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L7355
such attachment has been the use of a base having a socket
therein and a holder having a shank which engages such socket.
A clamping means such as for example a bolt is used to secure
the shank in the socket. This inYention relates to the means
by which the bit transmits forces to the holder and the holder
in turn transmits forces to the base. Such a socket type base
and holder are disclosed in U.S. Patent 3,992,061.
During mining operation the cutter bit is subjected
to extremely large mechanical forces of varying magnitude and
direction. One such mining operation for example is the use
of cutter mounted on a rotating cutter drum of a continuous
miner for coal mining. The first of such forces or cutting
force on a single cutter bit is generally tangentlal and varies
during a single revolution of the drum from a high cutting
force during contact with the coal, to low or negative force
when not contacting the coal. The magnitude of this cutting
force also varies within a single cutting stroke as the con-
sistency of the coal and its structural arrangement varies.
In addition to the actual cutting force it is
necessary to apply a normal pressure against the coal to force
the cutter into contact with the face. The second or normal
force is quite high during sumping or shearing operations.
Again the normal force varies during the cutting stroke
depending up the consistency and structure of the coal. This
normal force on the bit is generally direct inward toward the
axis of the drum during the cutting stroke. On the second
half of drum rotation, after completing the cutting stroke
when the bit is not contacting the coal, an outward force
and a tangentlal centrifugal force results due to the drum
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~1~7355
rotation and the bit support structures.
A third significant force present during cutting
operations is a side or latexal thrust generally perpendicular
to the plane of the cutting and normal forces described above.
This side thrust results from imperfections in the coal,
misalignment of the cutter, or side movement of the driving
mechanism such as for example cutting clearance with the
continuous miner drum. This side force tends to produce
rotation of the holder in the socket resulting in assembly
failure br poor cutting.
While other forces may be exerted on the cutter
assembIy during operation such other forces can usually be
resolved into components which act similar to the three forces
described above. Because of the magnitude and rate of change
of these forces it is of prime importance that holder
assemblies be capable of supporting the force load and retarding
the oscillations and movement associated with such quickly
changing loads. When the holder to base connection is given
any degree of movement, about the socket a~is such movement
~o results in unnecessary wear and premature failure. This
invention relates to a cutter assembly that provides support,
inhibits movement, and allows for easy removal and replacement
of its component parts~
As more support surfaces are added to the bit
holder, it becomes increasingly difficult to achie~e a proper
seating between the bit holder and the ~it base. This improper
seating is due to a number of causes including manufacturing
tolerances, normal wear on the base, and the presence of foreign
matter such as, for example, coal dust during a field replacement
pc/, '~
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of a bit holder. The U.SO Patent 3,992,061 explains and
solves some of the seating problems. But, the problem existed
of how to add load support surfaces which support against
the lateral forces in a manner which does not impair the
proper seating of the bit holder and base.
Previous holder and base assem~ly designs
concentrated on the ability to sustain the primary cutting
force and the normal force~ Such designs resulted in holders
which through their material bulk restrained some of the side
forces; but when such designs are subjected to severe duty
having high side loadings the life expectancy is greatly reduced.
While cutter bits may take many shapes, they
generally have a conical tip poxtion that actually engages
the material to be mined, and a body portion that is attached
to the holder. This invention relates to securing the body
portion of the bit to the holder. One such type of bit is a
bit having a generally conical tip portion and a shank portion
for insertion into a bore in the holder. This invention relates
to a means for supporting the bit within the hblder~
It is well known that a conical type bit which is
relatively free to rotate about the axis of the shank will
have a longer bit life and be more effective for cutting
operations. For this reason it is desirable to have a bit
shank of generally circular cross section which freely rotates
within the bore of the bit holder. The problem has been to
adequately support the-bit against the forces present in the
cutting operation and still permit the bit to freely rotate.
One method for holding the bit and allowing rotation has included
a sloping shoulder on the forward portion of the bit shank
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which bears upon a recessed surface on the front of the holder.
Such a forward shoulder is shown in U.S. Patent 3,499,685. This
type of shoulder support requires that the shoulder area transmit
the complete axial component of the cutting forces. Such large
forces on a small limited area result in wear due to friction.
Another method of supporting the bit includes a
rear surface on the ~it s~ank which engages a surface on a portion
of the holder. This rear support method simplifies the bit and
holder engagement but the bearing
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surface is limited to the cross~sectional area of the bit
shaf~ of shank. U.S. patents 3,397,012 and 3,554,605 show this
method of rear bit contact.
According to one aspect of the present invention there
is provided a cutter bit holder for securing a cutter bit to a
socket type base mounted on a driven mechanism, the holder
including a body portion with a cutter bit receiving bore and
a shank portion, at least one rear load bearing surface disposed
on the rear of the shank portion and at least one front load
bearing surface dispos~d on the front of the shank portion.
A forward extension portion is provided on the front of the
holder extending forward of the shank portion.
According -to another aspect of the present invention
there is provided a conical cutter bit for attachment to a
driven mining mechanism, the bit including a shaft portion of
circular cross section and a generally conical shaped tip
portion extending from one end of the shaft portion. An
annular load bearing surface is provided intermediate the shaft
portion and the tip portion, the annular surface being concentric
about the axis of the shaft portion, and the inner diameter
of the annular surface being generally equal to the diameter
of the shaft portion with the annular surface lying in a plane
generally perpendicular to the axis of the shaft portion
and facing generally away from the tip portion. The shaft
portion has a second load bearing surface on the end of the shaft
portion opposite the tip portion. The second surface lies in
a plane generally perpendicular to the axis of the shaft
portion and faces generally away from the tip portion.
The forward extension of the holder is provided
. ,
~4~
to gain a maximum movement arm about the axls of the holder
shank. The forward extension arm is engaged by the base so as
to inhibit rotation of the holder within the base. The
engagement of the forward e~tension is such that the holder is
free to travel to the rear as the holder is clamped in the
- socket. Such a rear movement allows for full and complete contact
between the load bearing surfaces located on the holder and
; on the base.
In a speci-fic embodiment of the invention, the forward
extension has load bearing surfaces on both sides so as to fit
into an upwardly open channel. The sides of the channel engage
the sides of the forward extension to retard rotational movement
between the base and holder about the axis of the socket.
In addition, the forward extension may have other surfaces
that add support forces to counter the cutting and normal forces.
: .
The bottom of the forward extension engages the bottom of the
channel to provide upward support opposing the normal force on
the bit.
In addition to supporting the holder to the base,
this invention provides for a secure mounting of the bit in
the holder. Bits of the type having flanges are used with the
flange contacting the orward end of the holder. The invention
also provides or support of the bit at the rear of the holder,
or for distributing the bit forces on the holder between a
front shoulder and a rear support or anvil on the holder.
One object of this invention is to provide an apparatus
for securing a cutter bit to a mining apparatus which distributes
the mining forces between forward and rearward load bearing
su~faces on the bit holder.
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:
These and other advantages of the present invention
will become more apparent upon references to the following
detailed specification and drawings.
DESCRIPTION OF THE DRAWINGS
E'ig. 1 is an outline of a side view of a miner
drum showing the position of eight bit bases, with four base,
holder and bit assemblies shown in partial detail.
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Fig. 2 is a side elevational view of a bit, holder
and base assembly, with the holder and bolt shown in partial
phantom.
Fig. 3 is a front elevational view of the assembly
of Fig. 2 with the socket and holder shank portion shown in
partial phantom.
Fig. 4 is a partial cross-sectional view taken along
~he line IV in Fig. 3.
Fig. 5 is a side elevational view of the holder.
Fig. 6 is a rear elevational view of the holder
shown in Fig. 5.
Fig. 7a is a side elevational view in partial
cross-section of an embodiment of a base, bit holder and
base assemhly with a holder having a rear tongue
- 11 --
,
. .
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and with bit contacting only the front shoulder of the
holder~
Fig. 7b is partial cross section of a side
elevational view of an assembly having a base and holder
similar to that in Fig. 7a with a cutter bit contacting
the holder at forward and rearward positions~ ~
~ig. 7c is a cross section of an assembly
havîng a base and holder similar to that in Fi~, 7a with
a pencil type cutter ~it contacting the tongue portion
of the holder.
~ig. 8 is a front elevational view o~ a bit,
bit holder, and base assembly with a clearance between
the forward extension and the extension support surface
of the ~ase. ` -
Fig. 9 is a partial cross section of the assem-
bly shown in Fig. 8 taken on line IX~
Fig. 10 is a top plan view of the bit~ holder
and base assembly shown in ~ig. 2.
Fig. 11 is a perspective view of the assembly
shown in Fig~ 2.
DESCRIPTION OF_PREFER~ED EMBODIMENTS
In the process~o~ mining a metal cutter ~it
.
is secured to apparatus which is advanced into contact
with a surface to dislodge earth, ore, or other beddea
materials. Fi~ure 1 shows a cross section of a mining
drum 11 with a number of cutter bits 2 attached to the
~ 12 -
mab/~,~fl
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periphery. The cutter bit 2 is part of an assem~ly 1
which is placed in spaced relationship around the drumO
The cutter drum.ll shows four bit assemblies 1 and our
positions 1' for attachment of additional bit assemblies.
It is to be understood that additional bit assemblies
can be attached to the drum in varying spaced relation-
ship, and as in the case of a continuous miner additional
bit assemblies are attached to khe drum along its longi-
tudinal axis. While the bit assemblies shown in Figure
1 are attached to the drum 11 in a symmetrical relation-
sh~p it is to be understood that the bit assemblies may
be angled or staggered with respect to one another so
that the bits engage the mined material at ~arying angles.
Each bit assembly 1 includes a conical bit 2, a bit
.
holder 3, and a. base 6. The base 6 is secured to the
drum 11 ~y a known means such as for example welding~
The base 6 has a threaded bolt 9 associated with it that
provides clamping support -to the bit holdex 3.. The bolt
9 is locked in place by nut 10~ The holder 3 has pro~
~ 20 vision for mounting and securing the bit 2. While the
: b~t assemblies 1 are shown mounted on a drum in Figure
1, it is to be understood that such bit assemblies may .
be mounted on other mining machines such as for example
cutter chains, conical head cutters, shearing machines,
or mining heads,
~ 13 -
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~473S~
As the drum 11 is rotated in the direction as shown
the bit 2 contacts the material to be mined and two primary
cutting forces Fl and F2 are exerted on the bit 2. Force Fl is
generally parallel to the direction of movement of the bit assembly
1, and as shown in Figure 1 this movement is tangential to the
arc inscribed by the bit during the rotation of thè drum 11.
The force F2 results from the drum being advanced into the
~aterial. F2 is generally acting perpendicular to Fl and generally
normal to the surface being mined. ~hile it is shown that forces
Fl and F2 act on the uppermost portion of the bit it is to be
understood that forces F1 and F2 are representative of similarly
directed forces acting upon the complete bit.
The forces Fl and F2 can be considered as a resulting
single force F5, as shown in Figure 2 which acts generally along
the axis of the bit 2 and in a direction tending to force the bit
2 into engagement wlth the holder 3.
As shown in Figure 2 the bit 2 has a tip 21 at its
uppermost portion and a cone portion 22 extending rearward from
the tipo The bit as shown in Figure 4 has a shaft portion 24
extending from the cone portion 220 To retain the bit within the
holder~ an annular groove 27 is pro~ided on the rear end of the
bit shaft 24. A retaining spring 8 is fitted into the groove 27
so that when the retaining spring 8 is expanded the bit shaft 24
can be inserted or removed from the bit holder 3.
The bit holder 3 includes a holding portion 30, a
shank portion 31 and a forward extension portion 32. The holding
portion 30 has a bore 33 extending through the holding portion 30.
The bit shaft ~4 has a circular cross section and is rotatably
fitted within the bore 33. As can be seen in Figure 4 the bit
- 14 -
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is retained within the bore 33 by the retaining spring 9 on oneend of shaft ~4 and b~ the engagement.of the flanged area 23 with
the holder portion 30. A rearward facing annular surface 25
on the bit flange 23 engages a corresponding annular load bearing
surface 45 on the holding portion 30. The engagement of these
two surfaces results in :~orces on the bit directed along the axis
B being transmitted to the bit holder.
In the embodiment shown in Figure 2 it is the
engagement of the annular suraces 45 and 25 that transmits force
~o F5 from the bit to the holder.
The base 6 has an upwardly open socket 63 into which
the bit shank portion 31 is inserted. The.socket 63 and shank
portion 31 provide means for.generally aligning and supporting
the holder within the base. The primar.y cutting forces are
transmitted from the holder 3 to the base 6 by means of load
. bearing surfaces on holder engaging. corresponding load bearing
surfaces on the base 6. The portion 30 of the holder has two
rearward extending legs 35a and 35b. Each of these legs has a
corresponding upper surface 36a and 36b respectiveIy, and a lower
surface 37a and 37b respectivelyO These load bearing surfaces
on the holder legs engage corresponding load bearing surfaces
on the base 6. The upper right leg surface 36a engages the upper
surface 66a on the base, and the upper surface 36b on the leg
engages the upper surface 66b on the base 6. The lower surface
37a on the holder engages the lo~er surface 57a on base 6, and
the lower surface 37b on the holder engages the lower surface 67b
on the base 6. These surfaces on the holder legs and their
respective surfaces on the base 6 transmit forces resulting from
the primary cutting surfaces preYiously described from the holder
- 15 -
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73~i5
3 to the base 6. It is apparent from the geometry as shown in
Figure 2 that these surfaces eEfectively transmit forces directed
parallel to the axis of the bit, which coincides with the axis
of the bore B as shown in Figure 4.
Referring to Figure 4 it can be seen that the
centerline or axis A of the soc~et 63 generally coincides to the
centerline or axis of the bit holder shank 31. When the bit
holder 3 is mounted in the base 6 the rear of the base 6 bears
upon the holder in three general locations. The three locations
include the leg 35a, leg 35b, and the rear shank surface 41.
The rear shank surface 41 bears upon the base 6 at the lower
rear base surface 61. Referring to Figure 4 shows that the
engagement between surfaces 41 and 61 does not restrict vertical
travel of the holder within the base 6 during clamping. The
threaded bolt 9 engages corresponding threaded portions of the
bore 71 as a means for providing a rearward clamping force on
the holder shank front load bearing surface ~2. As the clamping
bolt g is forceably rotated inward within bore 71 -the pressure
exerted on surface 42 causes the holder 3 to move rearward until
all three of the previously mentioned supporting locations have
been engaged. The parallel arrangement of surfaces 41 and ~2 allow
the legs 35a and 35b to properly seat within the notches formed
by surfaces 66a and 67a, and 66b and 67b respectively. When the
holder is firml~ secured within the base 6 the clamping holt 9
can be locked in place by nut 1~.
The clamping force exerted by the bolt 9 is directed
along a line which passes through the triangulation formed by the
three positions of rear support of the holder, namely leg 35a,
leg 35b, and the rear shank support surface 61. The clamping bolt
- 16 -
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73~
9 is positioned so that the clamping force transmitted by the
bolt 9 lies in a plane which passes between the holder legs 35a
and 35b. Figure 3 shows that the clamping bolt 9 is positioned
above the rear shank surface 41l and below the load bearing
surPaces on legs 35a and 35b.
Referring to Figure 5 a forward extension portion
32 of the holder 3 extends intermediate from and forward of
the holding portion 30 and the shank portion 31. This forward
extension portion provides for transmitting forces ~etween the
base 6 and the holder 3 at a further dis~ance from the centerline
A of the holder shank portion 31, than is available in a
conventional bit holder system. Support forces may be exerted
upon the side surfaces 3-8a and 38b of the forward extension 32
so as to inhibit rotation of the holder about the axis A of the
socket 63. Referring to Figure 3 shows the forward extension
32 having a right side surface 38a and a left side surface 38b
which are mated to contact corresponding load bearing surfaces
68a, 68b on the holder 6o Surface 38a contacts surface 68a and
surface 38b contacts load bearing surface 68b. In manufacturing
the tolerances between the surfaces 38 and surfaces 68 are held
to a minimum, such as for example .~lQ or less. When these
tolerances are so minimized, the surfaces in effect retard
rotation of the holder about its axis. As can be seen a portion
of the forward extension 32 resides within a channel 62 extending
forward from the socket in the ~ase 6. This upwardly open
channel 62 is formed by surfaces 68a, 68b, and 69 on the base 6.
The forward extension 32 in addition to pro~iding load bearing
surfaces -for engagement with corresponding base surfaces which
provide forces to retard or inhibit rotation of the holder within
- 17 -
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~ ~73~i~
the base 6, also provides additional upward support to the
holder by the corresponding engagement between the lower forward
extension surface 39 and the channel lower surface 69. The
engagement of surfaces 39 and 69 permit the base 6 to provide
upward support forces to the holder 3. The upward support forces
on the forward extension 32 counter the normal force F2. In
referring to Figure 4 it can be seen the engagement between
surfaces 39. and 69 provide upward support forces which are
directly below.forward portion of the bit formed by the bit cone
22 or bit tip 21. The forward positioning of the extension 32
provide for directly balancing force F2 without introducing any
additional toxque resulting. from the force couple of F2 and the
upward support forces on surface 39.
In the embodiment shown in Figures 8 and 9 the base
6 and the holder 3 have been-.configurated so that when the legs
t 35a and 35b are properly-seated in their respective.base positions
and the surfaces 41 and 61 are contacting each other, a minimal
space.16 is formed between the forward extension 32 and the
channel 62~ The sides of the channel 68a and 68b.are contacting
the respective sides of the forward extension 38a and 38b~ By
allowing the space 16 between surfaces 69 and 39 proper seating
at the legs 35a/ 35b and rear surface 41 are ensured because
:the holder is free to move both. rearward and in a vertical
direction as the clamping bolt is tightenedO In practice it is
found that if the vertical spacing between surfaces 39 and 69
is equal to or less than .02 inches this gap will quickly fill
with particles of the mined material such as for example coal
dust, and therefore provide a means of upward support to the
forward extension 32. By intentionally maintaining a small
- 18 -
P / ~) ,,,~
73~i~
tolerance between surfaces 62 and 42 the advantages of a tight
initial contact between the legs 35a and 35b in the base are
realized, and in addition after a short period of operation the
space 16 becomes compacted ~ith coal dust and functions as a
solid support between surfaces 62 and 42. As can be seen from
the drawings the axes of the bore, the shank portion, the bit
shaft and the socket all generally lie in a vertical plane that
bisects the mounting assemblyO
While the primary cutting forces Fl and F2 have
previously been described other forces are exerted on the cutter
bit during mining operationsO Figure 8 shows side forces F4 and
F3. These side forces are present during lateral movement of
the bito Such lateral forces are present during cutting or cross
cutting with the miner drum. Additional side forces are present
when the cutter bit assembly is mounted on a drum with the axis
of the bit extending at an angle from the plane which passes
through the bit tip and intersects the axis of the drum
perpendicularly. During normal operation of the cutting bit one
cause of the side forces F3 and F4 is due to varying consistency
of the mined material. The magnitudes of forces F3 and F4 can
vary rapidly over a wide range. Such rapidly varying would tend
to cause oscillation or chattering of the bit holder within the
bit blockD Such sus~ained oscillatory movement cause excessive
wear or premature breakage of the holder. As can be seen in
Figures 3 and 8 the engagement of ~he side surfaces 38a and 38b
on extension 32 by the inner surfaces 68a and 68b of the channel
62 in the base 6 provide substantial resisting forces at a
forward position or moment from the axis A. As can be seen in
Figure 4 the forward extension portion 32 provides the longest
:- -- 19 --
pc/~
735~
moment about a~is A of any surface on the holder which resists
rotation about the axis A. While the open socket 63 is of
rectangular horizontal cross sectional and the shank portion 31
of the holder 3 is of generally congruent rectangular horizontal
cross section it is not necessary that the lateral surfaces of
the holder shank 31 engage the.inner side surfaces of the socket
63. By maintaining a tolerance between the side surfaces of
the holder shank portion 31 and the.inner side portions of the
soc~et 63, holders 3 and base units 6.are readily interchangeable.
Such interchangeability is highly desirable because during the
life of a given base 6 many holders wilI be worn and require
replacement.
Figures 5 and 6 show the holder 3 with forward
extension 32 and bore 33. Figure 7a, b and c show an embodiment
of a holder 3' having a forward extension 32 and a support tongue
40. The tongue 40 extends up~ard and rearward from the holder
shank portion 31~ The upwardly .forward facing tongue surface 46
is a load bearing surface wh.ich contacts the rear surface 26 of
the bit to provide additional support for the bit in an axial
direction. Surface 46 is a planar surface lying within a circular
area having a radius equal~to the radius of the bore 33 and having
a center lying along the extension of the axis of the bore 33.
This additional support from surface 46 acts against F5. As
can be seen in Figure 7a bits having a shaft 24 of a shaft length
less than the distance from the holder annular surface 45 to the
tongue surface ~6 may be used. As shown-in Figure 7a, bit flange
23 is used to transmit the downward.axial forces from the ~it 2
to the bit holder 3. In the emb.odiment shown in Figure 7a a
rear clearance 17 is shown between the rear surface on the bit
- 20 -
pc/~,",/
~4~3~
26 and the tongue surface 46. For some specific mining appli-
cations where bit shaft rotation is a problem this method
is desirableO
Figure 7b shows a bit 2' having a shaft 24'
aligned within bore 33 of the holder 3'. The geometry between
shaft 24i and the holder 3l is such that simultaneous contact
between the bit annular suxface 25 and the holder annular
surface 45, and the bit rear surface 26' and the tongue surface
46 respectively. As can be seen the bearing surfaces on the
bit and the holder which provide support to forces directed
parallel to the axis of the bit shaft 24 and the bore 33,
namely surfaces 25, 45, 46 and 26 lie in planes which are
generally perpendicular to the axis of said shaft. Surfaces
lying in such perpendicular planes efficiently transmit the
primary cutting forces from the bit to the holder. Having
! the holder contact the bit at both the flange 23 and the rear
surface 26 increases the area of contact between the two
pieces and thereby reduce the frictional wear during rotation
of the bit.
Referring to-Figure 7c shows a pencil type bit
13 ~in a bit holder 3'. This bit has a bit shaft portion 14
which is of generally uniform circular cross sectional area.
The bit shaft 14 is free to rotate within the bore 33. The
primary cutting forces are transmitted along the axis of the
bit 13 to the interface between the rear bit surface 26' and
the tongue surface 46. The engagement between surface 26'
and 46 support the bit 13 against rear~ard axial movement
within the bore 33.
As can be seen by referring to Figures 7a, b and
pc/
c when a bit holder of the type 3' is used cutting bits of
various types may be used interchangeably with the same bit
holder 3'0 This interchangeability is important in mine
operation as different cutting bits may be used in the
mining machine for different operations without changing the
bit bases or bit holders. In addition,
- 22 -
~ ,, ,
pc/ ~j ,.
73~
if a mine operation is using a specific type of bit which
is temporarily unavailable he may substitute a variety of cutter
bits in his e~isting bit holders, thereby avoiding the necessity
to change bit holders or bases.
Figure 10 shows à top view of the bit..
holder and base assembly similar to that shown in Figure 2.
The axis A' of the holder shank portion is indicated at
its intersection ~ith the axis of the bit. The axis'A and
the axis A' generally coincide. It can be seen that the
forward extension 32 is fitted within the channel 62. The
support forces provided by the engagement of the forward extension
32 and the channel 62 can be seen to be acting at a considerable
distance or moment from the axis ~l., In addition, it can be
seen that the forward extension 32 is positioned beneath the
bit tip 21 and theforward portion of the bit cone 22; which
results in the upward support provided by the engagement of
surfaces 39 and 69 to be directed along the same line as but
opposing.the normal force F2.
The ahove-described base member and the overall assembly
are also described and are claimed in above-identified parent
Application Serial No. 336,238.
While the invention has been described in conjunction
with specific embodiments thereof it is evident that there are
many alternatives, modifications, and variations apparent to
those skilled in the art in view of the foregoing descriptions.
Accordingly, this application is intended to embrace all such
alternatives, modifications and variations as fall within the
spirit and scope of the appended claims.
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