U.S. patent application number 16/149205 was filed with the patent office on 2019-04-11 for bit holder.
The applicant listed for this patent is Wirtgen GmbH. Invention is credited to Karsten Buhr, Andreas Jost, Thomas Lehnert.
Application Number | 20190106988 16/149205 |
Document ID | / |
Family ID | 63708230 |
Filed Date | 2019-04-11 |
![](/patent/app/20190106988/US20190106988A1-20190411-D00000.png)
![](/patent/app/20190106988/US20190106988A1-20190411-D00001.png)
![](/patent/app/20190106988/US20190106988A1-20190411-D00002.png)
![](/patent/app/20190106988/US20190106988A1-20190411-D00003.png)
![](/patent/app/20190106988/US20190106988A1-20190411-D00004.png)
![](/patent/app/20190106988/US20190106988A1-20190411-D00005.png)
![](/patent/app/20190106988/US20190106988A1-20190411-D00006.png)
![](/patent/app/20190106988/US20190106988A1-20190411-D00007.png)
United States Patent
Application |
20190106988 |
Kind Code |
A1 |
Buhr; Karsten ; et
al. |
April 11, 2019 |
BIT HOLDER
Abstract
The invention relates to a bit holder for an earth working
machine, in particular a road milling machine, having a support
body onto which a holding portion having a bit receptacle, and
oppositely an insertion projection, are shaped. The holding portion
is terminated at the end by a wear surface, and the bit receptacle
by a centering receptacle opening in bevel fashion toward the wear
surface. A centering height, measured in the direction of the
longitudinal center axis, between an end of the centering
receptacle and the wear surface or a maximum point of a projection
projecting beyond the wear surface, is designed in such a way that
the ratio between the inside diameter D.sub.i of the bit receptacle
and the centering height is less than 8; and/or that the centering
height is greater than an axial play of a round-shank bit
installable in the bit holder; and that the support body comprises,
on its side facing away from the holding portion, at least two
bearing surfaces that are at an angle to one another and form a
bearing-surface pair. Reduced wear on the holding portion and a
reduced load on the insertion projection, and thus an extension of
the service life of the bit holder, are achieved.
Inventors: |
Buhr; Karsten; (Willroth,
DE) ; Jost; Andreas; (Konigswinter, DE) ;
Lehnert; Thomas; (Oberraden, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wirtgen GmbH |
Windhagen |
|
DE |
|
|
Family ID: |
63708230 |
Appl. No.: |
16/149205 |
Filed: |
October 2, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B28D 1/188 20130101;
E21C 35/19 20130101; E21C 35/197 20130101; E21C 35/1933 20130101;
E21C 35/18 20130101; E21C 35/191 20200501 |
International
Class: |
E21C 35/197 20060101
E21C035/197; E21C 35/193 20060101 E21C035/193 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 9, 2017 |
DE |
102017123368.7 |
Claims
1-11: (canceled)
12: A bit holder for an earth working machine, comprising: a
support body including a holding portion and an insertion
projection, the holding portion being located on a working side of
the support body, and the insertion projection extending from a
side of the support body opposite from the holding portion; the
holding portion including: a bit receptacle having a longitudinal
center axis and an inside diameter; a wear surface defined on an
end of the holding portion facing away from the support body, the
wear surface surrounding the bit receptacle and being configured
for abutment of a round-shank bit or of a support element for a
round-shank bit; a centering surface oriented obliquely to the
longitudinal center axis of the bit receptacle, the centering
surface connecting the bit receptacle and the wear surface and
defining a centering receptacle, the centering receptacle having a
centering height measured parallel to the longitudinal center axis,
the centering height extending between an end of the centering
receptacle facing away from the wear surface and a maximum point of
projection of the wear surface, a ratio of the inside diameter of
the bit receptacle to the centering height being less than 8.0;
wherein the support body includes at least one bearing surface on
the second side of the support body, the at least one bearing
surface extending on both sides of a center plane of the support
body including the longitudinal center axis of the bit
receptacle.
13: The bit holder of claim 12, wherein the ratio of the inside
diameter of the bit receptacle to the centering height is less than
7.5.
14: The bit holder of claim 12, wherein the ratio of the inside
diameter of the bit receptacle to the centering height is less than
7.0.
15: The bit holder of claim 12, wherein the ratio of the inside
diameter of the bit receptacle to the centering height is less than
6.5.
16: The bit holder of claim 12, wherein the maximum point of
projection surrounds the bit receptacle.
17: The bit holder of claim 12, wherein: the wear surface includes
a plurality of projections projecting beyond a lowest part of the
wear surface by the same or differing heights; and the centering
height is defined with reference to one of the projections having a
greatest height.
18: The bit holder of claim 12, wherein: the wear surface includes
a guidance groove defined in the wear surface and spaced away from
and surrounding the centering receptacle.
19: The bit holder of claim 18, wherein: the maximum point of
projection is located between the centering receptacle and the
guidance groove; and the centering receptacle has a greater depth
with respect to another portion of the wear surface adjacent the
guidance groove than does the guidance groove.
20: The bit holder of claim 12, wherein a transition between the
centering surface and the maximum point of projection is continuous
or rounded.
21: The bit holder of claim 12, wherein a height of the maximum
point of projection with respect to a lowest part of the wear
surface is greater than or equal to 0.3 mm.
22: The bit holder of claim 12, wherein the height of the maximum
point of projection with respect to a lowest part of the wear
surface is in a range of from 0.3 mm to 2.0 mm.
23: The bit holder of claim 12, wherein the height of the maximum
point of projection with respect to a lowest part of the wear
surface is in a range of from 0.5 mm to 1.5 mm.
24: The bit holder of claim 12, wherein the inside diameter of the
bit receptacle is equal to 20 mm and the centering height is
greater than 2.5 mm.
25: The bit holder of claim 12, wherein the inside diameter of the
bit receptacle is equal to 22 mm and the centering height is
greater than 2.75 mm.
26: The bit holder of claim 12, wherein the inside diameter of the
bit receptacle is equal to 25 mm and the centering height is
greater than 3.125 mm.
27: The bit holder of claim 12, wherein the inside diameter of the
bit receptacle is equal to 42 mm and the centering height is
greater than 5.25 mm.
28: The bit holder of claim 12, wherein the maximum point of
projection is formed on the wear surface by a material-removing
production method selected from the group consisting of turning,
sinking and milling.
29: The bit holder of claim 12, wherein the at least one bearing
surface comprises a bearing surface pair of two bearing surfaces on
opposite sides of the center plane.
30: The bit holder of claim 29, wherein the at least one bearing
surface further comprises at least one further bearing surface that
is at an angle to the two bearing surfaces of the bearing surface
pair.
31: The bit holder of claim 12, wherein the centering height is
greater than an axial play of a round-shank bit installed in the
bit holder.
Description
BACKGROUND OF THE INVENTION
1. Field of this Invention
[0001] The invention relates to a bit holder for an earth working
machine, in particular a road milling machine, having a support
body on which is shaped, in the region of a working side, a holding
portion into which a bit receptacle for reception of the shank of a
round-shank bit is shaped; the holding portion being terminated at
its end facing away from the support body by a wear surface,
enclosing the bit receptacle, for abutment of the round-shank bit
or of a support element; the bit receptacle being transitioned
indirectly or directly into the wear surface via a centering
surface, oriented obliquely to the longitudinal center axis of the
bit receptacle, of a centering receptacle; and an insertion
projection, for fastening the bit holder onto a base mount, being
shaped onto the support body on the side located oppositely from
the holding portion.
2. Description of the Prior Art
[0002] Earth working machines are used to carry out milling tasks
on hard substrates, for example on roads. Such machines each
comprise a rotating milling drum. Fastened on the milling drum are
a plurality of bits that, as a result of the rotation of the
milling drum, penetrate into the substrate and remove it. The bits
are subjected to considerable wear in this context. It is therefore
known to fasten the bits replaceably on a milling drum tube of the
milling drum. Base mounts can be mounted for that purpose fixedly,
for example by welding, on the milling drum tube. A bit holder can
then be detachably fastened on such a base mount. The bit holder
comprises a bit receptacle in which a bit can also be detachably
installed. Worn bits can thus easily be replaced. If the bit holder
is also worn down after several bit changes, it can be detached
from the base mount and replaced. It is known to mount the bits in
the bit holder rotatably around their longitudinal axis and in
axially immobilized fashion. The bits rotate around their
longitudinal axes during the milling process, with the result that
a bit tip or bit head engaging into the substrate becomes evenly
worn over its periphery. In order to absorb axially acting forces,
the bit head abuts against the bit holder directly or with
interposition of a support element. As a result of the rotation,
the bit holder is subjected to increased wear in the region where
the bit head or support element rests. In addition to the axial
forces, large transverse forces also act on the bit during earth
working. These result in uneven erosion of the bit holder in the
region where the bit head or support element rests. They also
result in large forces at the transition from the bit holder to the
base mount. If the bit holder wears unevenly, free rotatability of
the bit is then limited and in particular it then tends to jam. If
the rotatability of the bit is limited, however, it no longer wears
evenly along its periphery in the desired manner. What occurs
instead is one-sided wear, which leads to premature tool
failure.
[0003] DE 10 2014 104 040 A1 (US 2017/030191) discloses a bit, in
particular a round-shank bit, having a bit head and a bit shank.
The bit is held with its bit shank in a cylindrical bit receptacle
of a holding projection of a bit holder. For that purpose the bit
shank is fastened in the bit receptacle, by means of a fastening
sleeve, rotatably around its longitudinal center axis but in
axially immobilized fashion. The bit head, whose diameter is larger
as compared with the bit shank, rests, at the end and surroundingly
with respect to the bit receptacle, on a wear surface of the
holding projection via a disk-shaped support element. The holding
projection is of cylindrical configuration. Oppositely from the
bit, the holding projection is connected to a base part of the bit
holder. The base part extends transversely with respect to the
holding projection. Shaped onto the base part in laterally offset
fashion, and located oppositely from the holding projection, is an
insertion projection that serves to fasten the bit holder to an
above-described base mount of a milling drum. The bit receptacle is
embodied as a passthrough orifice that passes through the holding
projection.
[0004] The bit receptacle widens toward the bit into a centering
receptacle. The surface of the centering receptacle is oriented
obliquely to the longitudinal center axis of the bit receptacle. It
transitions via a ridge into the wear surface of the holding
projection. The ridge projects out beyond the wear surface. That
surface of the support element which faces toward the holding
projection is embodied complementarily to the end face of the
holding projection. The support element rests with a seating
surface on the wear surface of the holding projection. Shaped into
the support element in the region of the ridge is a surrounding
groove that receives the ridge. A centering projection of the
support element, projecting beyond the seating surface, engages
positively into the centering receptacle of the bit holder. The
support element is guided in a radial direction thanks to the
engagement of the centering projection into the centering
receptacle, and of the ridge into the groove.
[0005] Axial play of the bit in the bit mount is necessary in order
to ensure rotatability of the bit around its longitudinal center
axis. A larger axial play is provided for larger bits than for
smaller bits. If the axial play exceeds the height of the centering
receptacle, lateral guidance of the support element by the
centering projection is lost. This results in elevated and uneven
wear on the bit holder, thereby shortening its service life. This
is true especially in the context of the large transverse forces
that are transferred from the bit head via the support element to
the wear surface of the holding projection and result in uneven
abrasion there when the support element is not guided exactly. At
the same time, the large transverse forces result in heavy loads on
the insertion projection and on the fastening elements with which
the insertion projection is held in the base mount. Those forces
can result in fatigue breakages at the insertion projection or in
wear on or detachment of the fastening elements, and thus in damage
to or loss of the bit holder having the bit mounted thereon.
[0006] EP 1 427 913 B1 (U.S. Pat. No. 6,824,225) discloses a
subassembly having a rotatable cutting bit and a disk. The disk
comprises ribs on its front side facing toward the head of the
cutting bit, and recesses on its oppositely located rear side,
thereby improving the rotatability of the disk around its center
axis. Shaped onto its rear side, surroundingly and adjacently to a
central orifice, is a centering projection having a surface
oriented obliquely to the center axis. When the bit is installed,
the centering projection engages into a bevel mounted at the end on
a cylindrical bit receptacle of a bit holder. The disk is thereby
laterally guided. The bevel protrudes only slightly beyond the rear
side of the disk. As a result of the required axial play of the
cutting bit, the centering projection can be shifted out of
engagement with the bevel so that its lateral guidance is lost.
This results in elevated wear on both the disk and the bit holder,
especially when large transverse forces are acting on the bit.
SUMMARY OF THE INVENTION
[0007] The object of the invention is to furnish a bit holder for
an earth working machine, in particular a road milling machine,
which has a long service life.
[0008] The object of the invention is achieved in that a centering
height, measured in the direction of the longitudinal center axis,
which extends between an end of the centering receptacle facing
away from the wear surface and a maximum point of a projection
projecting beyond the wear surface, is designed in such a way that
the ratio between the inside diameter of the bit receptacle and the
centering height is less than 8; and/or that the centering height
is greater than an axial play of a round-shank bit installed in the
bit holder; and that the support body comprises one or several
bearing surfaces on its side facing away from the holding portion,
the one bearing surface extending on both sides of a center plane
that receives the center axis and extends in the advance direction,
or that at least one bearing surface respectively extends on both
sides of that center plane.
[0009] The centering receptacle serves to receive and guide a
centering projection of a support element that can be arranged
between a round-shank bit and the holding portion of the bit
holder, or a centering projection shaped directly onto the
round-shank bit if the latter abuts against the holding portion
with no interposed support element. The centering projection is
embodied complementarily in terms of shape with respect to the
centering receptacle, and projects beyond a surface (seating
surface or resting surface), facing toward the bit holder, of the
support element or of the bit head. The centering projection is
thus in engagement with the centering receptacle, and the support
element or the round-shank bit is thereby radially guided. If a
projection is shaped on in the region of the wear surface of the
bit holder, that projection engages into a corresponding recess in
the seating surface of the support element or in the resting
surface of the bit head. Additional lateral guidance of the support
element or of the bit head is thereby achieved. The result of the
feature that the ratio between the inside diameter D.sub.i of the
bit receptacle and the centering height is less than 8 is to ensure
sufficient immobilization, or reduction of a lateral motion, of the
support element or of the round-shank bit with respect to the bit
holder. The centering height can be selected to be greater than the
maximum axial play of the round-shank bit which is to be expected
over the life expectancy of the round-shank bit. For large
round-shank bits having correspondingly large bit shanks, the axial
play is greater than for comparatively small round-shank bits. This
is taken into account by specifying the numerical ratio between the
inside diameter D.sub.i of the bit receptacle and the centering
height. Good lateral guidance of the support element or of the
round-shank bit is thus ensured, for all bit sizes being used, when
a bit is withdrawn maximally out of the bit receptacle within the
axial play. Longitudinal wear on the holding portion of the bit
holder can be minimized thanks to the small lateral motion of the
support element and of the round-shank bit. This also applies in
particular in a context of large transverse forces acting on the
round-shank bit, which are transferred onto the wear surface of the
bit holder via the support element or directly from the bit head.
With insufficient lateral guidance of the support element or
round-shank bit, such uneven loads on the wear surface cause
asymmetrical and thus more intense wear on that surface. Wear on
the bit holder, in particular when large transverse forces occur,
is thus significantly reduced because of the embodiment according
to the present invention of the centering receptacle and, if
applicable, of the projection as a function of the diameter of the
bit receptacle. As a result thereof, the bit holder needs to be
replaced significantly less often.
[0010] As already stated earlier, large transverse forces also
result in heavy loading of the insertion projection and of the
fastening elements with which the insertion projection of the bit
holder is held in the base mount. In order to adapt the service
life of the fastening system for the bit holder to the extended
service life of the holding portion, provision is made according to
the present invention that the support body comprises, on its side
facing away from the holding portion, at least two bearing surfaces
(first or second bearing surfaces) constituting a bearing-surface
pair, which are at an angle to one another. When the bit holder is
installed, these bearing surfaces abut against corresponding
support surfaces of the base mount on which the bit holder is
fastened with its insertion projection. Forces transferred to the
round-shank bit and thus to the bit holder are discharged to the
base mount both via the insertion projection and via the bearing
surfaces. Stresses on the insertion projection and its fastening
elements are thereby reduced, with the result that premature wear
on or breakage of the insertion projection and the fastening
elements can be avoided. In particular, large transverse forces can
be transferred to the base mount by the bearing surfaces at an
angle to one another. The bearing surfaces are preferably oriented
in such a way that the forces to be transferred from the bearing
surfaces to the support surfaces are oriented substantially in the
direction of the surface normal line of one of the bearing surfaces
or support surfaces. Because the bearing surfaces are at an angle
to one another and constitute a bearing-surface pair, the support
body and thus the bit holder can preferably be embodied
symmetrically. The bit holder can thus be used at all positions on
the milling drum which, for example, are oriented in mirror-image
fashion with respect to one another on the opposite sides of the
milling drum.
[0011] The centering receptacle, in interaction with the centering
projection, also results in a labyrinth-like seal. Wear on the bit
is thereby reduced. The sealing effect can be further improved by
projections that are arranged on the wear surface and engage into
recesses corresponding thereto.
[0012] According to a preferred variant embodiment of the
invention, provision can be made that the ratio between the inside
diameter D.sub.i of the bit receptacle and the centering height is
less than 7.5, preferably less than 7.0, particularly preferably
less than 6.5. With a ratio of less than 7.5, good lateral guidance
is achieved even when transverse forces act directly on the support
element or on the round-shank bit, for example as a result of
impacts of removed material. A ratio of less than 7.0 again
improves lateral guidance, so that even the simultaneous action of
axially oriented forces unevenly distributed over the support
element and radially acting transverse forces does not result in a
tumbling motion of the support element with consequently severe
wear. With a ratio of less than 6.5, sufficient lateral guidance is
achieved even toward the end of the service life of the support
element and of the round-shank bit, when the axial play of the
round-shank bit may have become impermissibly large due to the wear
that has already occurred.
[0013] Radially acting guidance of the support element and/or of
the round-shank bit, along with good rotatability of the support
element and/or of the bit, can be achieved by the fact that the
projection is arranged surroundingly with respect to the bit
receptacle.
[0014] Lateral guidance of the support element can furthermore be
improved by the fact that several projections of the same or
different height can be shaped onto the wear surface of the holding
portion; and that the ratio between the inside diameter D.sub.i of
the bit receptacle and the centering height with respect to one of
the projections, preferably the ratio between the inside diameter
D.sub.i of the bit receptacle and the greatest centering height
determined with respect to a projection, is less than 8.
[0015] With several projections that are arranged radially next to
one another and engage into recesses corresponding thereto, the
projected area of the wear surface in an axial direction is
maintained but the contact surface between the bit holder and the
support element or the round-shank bit in a radial direction is
enlarged. Greater transverse forces can be absorbed as a result. At
the same time, the contact area between the bit holder and the
support element or round-shank bit is enlarged, which has a
positive effect on wear behavior. The sealing effect with regard to
penetration of removed material is furthermore considerably
improved thanks to the juxtaposition of the projections and the
recesses that receive the projections. As a result of the ratio of
less than 8 between the inside diameter D.sub.i of the bit
receptacle of the bit holder and the centering height, sufficient
radial guidance of the support element and of the round-shank bit
is achieved even when a support element or round-shank bit is
raised maximally off the wear surface in the context of the axial
play.
[0016] A further improvement in lateral guidance can be achieved in
that a guidance groove is shaped into the adjacent wear surface,
spaced away from and surroundingly with respect to the centering
receptacle. The guidance groove makes it possible for a guidance
land, shaped onto the support element or round-shank bit, to engage
thereinto. The rotatability of the support element or round-shank
bit is thereby improved, resulting in decreased longitudinal wear
on the holding portion of the bit holder.
[0017] Good rotatability of the support element or round-shank bit
can be achieved by the fact that the projection is embodied between
the centering receptacle and the guidance groove; and that the
centering receptacle has, with respect to the adjacent wear
surface, a greater depth than the guidance groove. Three-point
radial guidance of the support element or of the round-shank bit on
the bit holder is thereby achieved, namely in the region of the
centering receptacle, at the projection, and at the guidance
groove.
[0018] The rotatability of the support element or of the
round-shank bit can be further improved by the fact that
transitions between the centering surface, the wear surface, the
projection, and/or the guidance groove proceed in continuous or
rounded fashion. Sharp edges and rotation-blocking edges are
thereby avoided.
[0019] Good lateral guidance of the support element or of the
round-shank bit can result from the fact that the height of the
projection with respect to the wear surface is greater than or
equal to 0.3 mm, preferably between 0.3 mm and 2 mm, particularly
preferably between 0.5 mm and 1.5 mm. A sufficient improvement in
lateral guidance of the support element or round-shank bit cannot
be achieved with a projection smaller than 0.3 mm. Good lateral
guidance of the support element or round-shank bit can be attained
with a projection in the range between 0.3 mm and 2 mm. Projections
having a height of between 0.5 mm and 1.5 result in particular in
good rotatability of the support element or the round-shank
bit.
[0020] For usual bit sizes and associated bit holders, provision
can be made that the inside diameter D.sub.i is equal to 20 mm and
the centering height is greater than 2.5 mm; and/or that the inside
diameter D.sub.i is equal to 22 mm and the centering height is
greater than 2.75 mm; and/or that the inside diameter D.sub.i is
equal to 25 mm and the centering height is greater than 3.125 mm;
and/or that the inside diameter D.sub.i is equal to 42 mm and the
centering height is greater than 5.25 mm. For smaller bits, for
example for precision milling, bit receptacles having an inside
diameter D.sub.i of 20 mm or 22 mm and a centering height
respectively of at least 2.5 mm or 2.75 mm are suitable. For
medium-sized bits, bit receptacles having an inside diameter
D.sub.i of 25 mm and a centering height of 3.125 mm are suitable.
For large bits and associated bit holders, bit receptacles having
an inside diameter D.sub.i of 42 mm with a centering height of at
least 5.25 mm can be used. With a ratio of less than 8 between the
inside diameters D.sub.i of the bit receptacles and the respective
centering height, suitable centering projections are provided for
all usual sizes of the support elements or round-shank bits. This
ensures that sufficient lateral guidance of the support elements or
of the bit exists, for example, for larger bits with
correspondingly greater forces that occur, and for a larger axial
bit play.
[0021] Suitable projections or guidance grooves can be furnished by
the fact that the projection and/or the guidance groove is produced
on the wear surface by way of a material-removing production method
in the context of manufacture of the bit holder. When the
projection and/or guidance groove are already produced on the wear
surface during manufacture of the bit holder, the bit shank and the
bit receptacle are then protected by the resulting labyrinth-like
seal from the entry of dirt as soon as operation begins. Good
lateral guidance already exists when the bit holder is new, so that
less wear is present from the outset.
[0022] Discharge of transverse forces acting on the bit, via the
bit holder to the base mount, can be improved by the fact that the
support body comprises at least one further bearing surface that is
at an angle to the two bearing surfaces of the bearing-surface
pair. The at least three, particularly preferably four bearing
surfaces are preferably oriented in such a way that at least one of
the surface normal lines of the bearing surfaces proceeds at least
approximately in the direction of the force action in the context
of the transverse forces that can possibly occur. The force can
thus preferably be transferred from the bearing surfaces, oriented
transversely to it, to the base mount. Substantial relief of the
load on the insertion projection of the bit holder is thereby
achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention will be explained in further detail below with
reference to an exemplifying embodiment depicted in the drawings,
in which:
[0024] FIG. 1 is a perspective side view of a bit holder connected
detachably to a base mount;
[0025] FIG. 2 is an exploded view of the base mount with bit holder
shown in FIG. 1;
[0026] FIG. 3 is a front view of the bit holder shown in FIGS. 1
and 2;
[0027] FIG. 4 is a rear view of the bit holder shown in FIGS. 1, 2,
and 3;
[0028] FIG. 5 is a detail of a tool system with a respective detail
of a holding portion of the bit holder, a support element, and a
round-shank bit held in the bit holder;
[0029] FIG. 6 schematically depicts the wear on a wear surface of a
known bit holder; and
[0030] FIGS. 7 to 15 are respective schematic lateral section views
of a detail of a holding portion in the region of a centering
receptacle.
DETAILED DESCRIPTION
[0031] FIG. 1 is a perspective side view of a bit holder 20
detachably connected to a base mount 10. Oppositely from bit holder
20, base mount 10 is terminated by a concavely shaped lower
terminating side 11. With this terminating side 11, base mount 10
can be fastened onto a milling drum tube (not shown) of an earth
working machine, in the present case a road milling machine. Base
mount 10 is preferably welded onto the milling drum tube so that
large forces can be transferred. A base body 13 of base mount 10
has, at the front in a working direction, two inclined surfaces 15
arranged at an angle to one another and symmetrically with respect
to one another in terms of a longitudinal center plane of base
mount 10. Adjoining these at an angle are two oblique surfaces 14
arranged in mirror-image fashion with respect to the longitudinal
center plane of base mount 10, only one of which is evident from
the present perspective. Oblique surfaces 14 transition angularly
into lateral surfaces of base body 13. The lateral surfaces are
preferably oriented parallel to the working direction of base mount
10 during operation on a milling drum. The arrangement of inclined
surfaces 15, oblique surfaces 14, and the adjoining lateral
surfaces causes removed material to slide laterally past base mount
10.
[0032] Bit holder 20 comprises a support body 21 that is terminated
at the front by a skirt 22. A holding portion 30 is shaped onto
support body 21, facing away from base mount 10. Holding portion 30
is cylindrical in shape. Oppositely from support body 21, holding
portion 30 is terminated by a wear surface 31. Wear surface 31 is
arranged surroundingly with respect to a bit receptacle 32 of bit
holder. Bit receptacle 32 is constituted by a cylindrical orifice;
it is oriented along a longitudinal center axis M shown in FIGS. 6
to 15. Bit receptacle 32 widens in a beveled shape at its end
facing toward wear surface 31, in the region of a centering
receptacle 33. A projection 34, embodied in the present case in a
ridge shape, is shaped on wear surface 31 surroundingly with
respect to centering receptacle 33, and projects beyond the latter
parallel to longitudinal center axis M. Wear markings 30.1 are
provided on the outer surface of holding portion 30. Wear markings
30.1 are embodied in the present case as circumferential grooves.
They are arranged at different distances from wear surface 31.
Longitudinal wear on holding portion 30 can be recognized and
evaluated on the basis of wear markings 30.1. Bit holder 20 is
embodied symmetrically with respect to a transverse center plane MQ
shown in FIGS. 3 and 4. That transverse center plane MQ receives
longitudinal center axis M of bit receptacle 32 and extends in
advance direction V, as is evident from FIGS. 3 and 4. Those
surfaces of support body 21 and of skirt 22 which face away from
base mount 10 constitute deflection surfaces for the removed
material. They are oriented obliquely to transverse center plane MQ
so that a land 26 oriented in the direction of transverse center
plane MQ is formed in front of holding portion 30 in a working
direction.
[0033] FIG. 2 is an exploded view of base mount 10, with bit holder
20, shown in FIG. 1. An insertion projection 40 is shaped onto
support body 21 on that side of support body 21 which is located
oppositely from holding portion 30 of bit holder 20. Insertion
projection 40 is connected to support body 21 with an offset, in
working direction V of bit holder 20, from holding portion 30. Said
projection is oriented in its longitudinal extent toward base mount
10. Two abutment surfaces 41, only one of which is evident in the
selected perspective, preferably project beyond the surface of
insertion projection 40 in the working direction. In the context of
the invention, a compression bolt receptacle 42 in the form of a
recess is shaped into the insertion projection oppositely from the
working direction. Compression bolt receptacle 42 is preferably
terminated in a direction toward base mount 10 by a compression
surface 42.1 proceeding obliquely to the longitudinal dimension of
insertion projection 40.
[0034] Base mount 10 is penetrated by an insertion receptacle 16.7.
Insertion receptacle 16.7 is oriented toward insertion projection
40 of bit holder 20. It serves to receive insertion projection 40.
A threaded receptacle 18 is shaped into base mount 10, proceeding
obliquely to insertion receptacle 16.7. It opens at the end into
insertion receptacle 16.7. A compression bolt 50 is associated with
threaded receptacle 18. Compression bolt 50 comprises a threaded
portion 51, a tool receptacle 53, and a compression projection 52
located oppositely from tool receptacle 53. Said bolt can be
screwed into threaded receptacle 18 of base mount 10 in such a way
that compression projection 52 projects into insertion receptacle
16.7.
[0035] Laterally and frontwardly in the working direction,
insertion receptacle 16.7 transitions into first support surfaces
16.1. The latter are oriented obliquely slopingly toward insertion
receptacle 16.7, and symmetrically with respect to a center plane
of base mount 10.
[0036] A surface 17 is embodied surroundingly with respect to
threaded receptacle 18. Said surface is delimited laterally by
protrusions projecting beyond surface 17. Toward insertion
receptacle 16.7, the projections form two support surfaces 16.2.
The latter are oriented at an angle to one another and obliquely
slopingly with respect to insertion receptacle 16.7 and the center
plane of base mount 10. They are furthermore arranged at an angle
to first support surfaces 16.1. First and second support surfaces
16.1, 16.2 thus each constitute abutment surfaces, oriented in
prism-shaped fashion toward one another, for support body 21 of bit
holder 20. First and second support surfaces 16.1, 16.2 are
oriented at an angle toward one another and are inclined slopingly
toward insertion receptacle 16.2. Resetting spaces 16.3, 16.4,
16.5, in the form of depressions, are embodied along the angular
transitions between support surfaces 16.1, 16.2. Resetting space
16.5 embodied between the two support surfaces 16.2 transitions via
a cutout 16.6 into surface 17 that delimits threaded receptacle
18.
[0037] Insertion receptacle 16.7 and the delimiting support
surfaces 16.1, 16.2 constitute a bit holder receptacle 16.
[0038] Bit holder 20 shown in FIGS. 1 and 2 is depicted in a front
view in FIG. 3 and in a rear view in FIG. 4. Advance direction V,
and thus the working direction of bit holder 20, are labeled in
FIGS. 3 and 4 with the usual arrow depiction. Transverse center
plane MQ proceeding in advance direction V forms a plane of
symmetry of bit holder 20. As shown in FIG. 3, skirt 22 of support
body 21, facing in advance direction V, forms on its side facing
toward insertion projection 40 two first bearing surfaces 23
oriented at an angle to one another. First bearing surfaces 23 are
preferably arranged mirror-symmetrically with respect to transverse
center plane MQ. An asymmetrical arrangement is also conceivable.
Bearing surfaces 23 are oriented to proceed obliquely to transverse
center plane MQ. First bearing surfaces 23 form a first
bearing-surface pair. A transition portion 23.1 can be provided
between first bearing surfaces 23. First bearing surfaces 23
transition into insertion projection 40, preferably via a fillet
transition 23.2. Insertion projection 40 comprises, in advance
direction V, the two abutment surfaces 41 arranged
mirror-symmetrically with respect to transverse center plane MQ.
They can be separated from one another by a recess 43.
[0039] As depicted in FIG. 4, support body 21 forms second bearing
surfaces 24 on its rear portion with respect to advance direction
V, on its surface facing toward insertion projection 40. Second
bearing surfaces 24 are oriented angularly and, with respect to
transverse center plane MQ, preferably in mirror-image fashion with
respect to one another. Second bearing surfaces 24 can of course
also be located on both sides of transverse center plane MQ and do
not need to be mirror images of one another. They can transition
into insertion projection 40 via a fillet transition 24.2 or in
sharp-edged fashion. An indirect transition is also conceivable.
Second bearing surfaces 24 form a second bearing-surface pair. They
can be separated from one another, for example, via a transition
portion 24.1 embodied in throat-shaped fashion. Transition portion
24.1 can preferably proceed along transverse center plane MQ of bit
holder 20. Bit receptacle 32, embodied as a passthrough orifice,
opens into transition portion 24.1. A throat-shaped flushing
channel 25 is guided to bit receptacle 32 oppositely to advance
direction V. Flushing channel 25 forms a radially oriented opening
in bit receptacle 32. Through it, removed material introduced into
bit receptacle 32 during a milling process can be discharged
outward.
[0040] For purposes of the present invention, for example, first
bearing surfaces 23 can be interpreted as bearing surfaces of the
bearing-surface pair, and one or both of second bearing surfaces 24
as (a) further bearing surface(s). Conversely, the two second
bearing surfaces 24 can also form the bearing surfaces of the
bearing-surface pair, and one or both first bearing surfaces 23
then form the further bearing surface(s). The "first/second bearing
surfaces 23/24" terminology will continue to be used
hereinafter.
[0041] For installation of bit holder 20 on base mount 10 shown in
FIG. 2, insertion projection 40 is inserted into insertion
receptacle 16.7 until support body 21 abuts with its first bearing
surfaces 23 against first support surfaces 16.1, and with its
second bearing surfaces 24 against second support surfaces 16.2, of
base mount 10. Bearing surfaces 23, 24 and the associated support
surfaces 16.1, 16.2 are each correspondingly oriented identically
for that purpose. When bit holder 20 is completely inserted,
compression bolt 50 is screwed into threaded receptacle 18 on base
mount 10, in which context compression projection 52 engages into
compression bolt receptacle 42 of insertion projection 40 and abuts
at the end against compression surface 42.1. Bit holder 20 is
thereby axially immobilized by compression bolt 50. Because of its
orientation proceeding obliquely to the longitudinal dimension of
insertion projection 40, compression bolt 50 presses the latter
with its abutment surfaces 41 against the wall of insertion
receptacle 16.7. At the same time, compression bolt 50 secures
first and second bearing surfaces 23, 24 with respect to the
associated first and second support surfaces 16.1, 16.2.
[0042] Bearing surfaces 23, 24 that proceed inclinedly with respect
to insertion projection 40 make possible an optimized transfer of
force to base mount 10 in a context of transverse forces acting
from different directions on bit holder 20 and varying forces
acting oppositely to advance direction V, since at least one of
bearing surfaces 23, 24 is oriented with its surface normal line
approximately in the direction of the resulting applied force.
Force transfer from bit holder 20 to base mount 10 is thus
accomplished in large part from bearing surfaces 23, 24 onto the
corresponding support surfaces 16.1, 16.2. Loads on insertion
projection 40 are thereby relieved, in particular in its transition
region to support body 21. Premature fatigue breakage of insertion
projection 40 can thus be avoided.
[0043] FIG. 5 shows a detail of a tool system with a respective
detail of holding portion 30 of bit holder 20, a support element
70, and a round-shank bit 60 held in bit holder 20.
[0044] A bit head 61 of round-shank bit 60 is terminated, toward
holding portion 30 of bit holder 20, by a collar 62. Collar 62
constitutes a resting surface 62.1 in a direction toward holding
portion 30. That surface rests on a support surface 72 of support
element 70. Support surface 72 is constituted inside a receptacle
71 on the upper side of support element 70, and is correspondingly
delimited externally by a rim 71.1. On the sides located opposite
support surface 72, support element 70 comprises a seating surface
73 with which it rests on wear surface 31 of holding portion 30 of
bit holder 20. Support element 70 is constructed substantially
rotationally symmetrically with respect to a longitudinal center
axis of round-shank bit 60. Seating surface 73 transitions via a
surrounding recess 75 into a counterpart centering surface 74.1,
proceeding inclinedly with respect to the longitudinal center axis
of support element 70, of a centering projection 74. As is clearly
illustrated by FIG. 5, centering projection 74 of support element
70 is inserted into the correspondingly shaped centering receptacle
33 of bit holder 20. Counterpart centering surface 74.1 thus abuts
against a corresponding centering surface 33.1 of centering
receptacle 33. Projection 34 of holding portion 30 engages into
recess 75.
[0045] Support element 70 has, along the longitudinal center axis,
a receiving orifice 77 by which a guidance region 76 is constituted
for guidance of round-shank bit 60. In the installed position
shown, a centering portion 63 of a bit shank of round-shank bit 60
is associated with guidance region 76. A pivot bearing mount is
thereby produced between guidance region 76 and centering portion
63. Care should be taken here that the outside diameter of the
cylindrical centering portion 63 is coordinated with the inside
diameter of receiving orifice 77 in guidance region 76 in such a
way that free rotatability between support element 70 and centering
portion 63 is maintained. The play between those two components
should be selected so that the least possible lateral offset
(transversely to the longitudinal center axis of round-shank bit
60) occurs. Centering portion 63 transitions, after a taper region
63.1, into the cylindrical bit shank that is concealed in the
present case by a fastening sleeve 64.
[0046] The bit shank is retained axially by means of fastening
sleeve 64 in bit receptacle 32 on holding portion 30 of bit holder
20. The retention permits an axial play 80. Fastening sleeve 64
comprises a bevel at its upper end.
[0047] During operation, round-shank bit 60 can rotate around its
longitudinal center axis. The free rotatability ensures that
round-shank bit 60 wears evenly over its entire circumference.
Support element 70, which is loosely placed on and held by
centering portion 63 of the bit shank, also rotates in this
context, with the result that the overall rotatability of
round-shank bit 60 is further improved. The rotation and the high
mechanical loading of round-shank bit 60 cause wear to occur on bit
holder 20, principally in the upper portion of holding portion 30.
The load causes wear surface 31 to be worn away. The wear existing
on holding portion 30 can be evaluated by way of wear markings
30.1.
[0048] The engagement of centering projection 74 into centering
receptacle 33, and of projection 34 into recess 75, results in
lateral guidance of support element 70, which has a positive effect
on the rotatability of support element 70 and thus of round-shank
bit 60. Centering surface 33.1 transitions tangentially into the
surface of projection 34. Farther on, the surface of projection 34
is transitioned in rounded fashion into wear surface 31.
Correspondingly, counterpart centering surface 74.1 of centering
projection 74 of support element 70 transitions tangentially into
recess 75, and the surface of recess 75 transitions in rounded
fashion into seating surface 73 of support element 70. Edges that
impede the rotatability of support element 70 and thus of
round-shank bit 60 are thereby avoided. With its radial outer
surface portion, projection 34 counteracts forces that act radially
inward on support element 70. Forces directed radially outward are
counteracted by the radially inner surface portion of projection
34. The force that must be absorbed by centering surface 33.1 of
holding portion 30 is thereby reduced, resulting in decreased
surface pressure, and correspondingly decreased wear, in this
region. Guidance by projection 34 furthermore counteracts a
tumbling motion in the disk plane of support element 70, producing
a further reduction in wear at bit holder 20.
[0049] FIG. 6 schematically depicts the wear on wear surface 31 of
a known bit holder 30 in the context of an asymmetrical load on
support element 70 that is shaped complementarily to wear surface
31 and to centering receptacle 33. In the embodiment shown, the
disk-shaped support element 70 is delimited by a flat support
surface 72 and by an oppositely located, likewise flat, seating
surface 73. Centering projection 74 is shaped on seating surface 73
with its counterpart centering surface 74.1 surrounding the central
receiving orifice 77. Receiving orifice 77 has, on the side of
support surface 72, an introduction chamfer 76.1 that facilitates
insertion of the bit shank.
[0050] The asymmetrical load is depicted by way of two arrows of
different lengths which symbolize a first force 83.1 and a second
force 83.2 greater compared thereto. The asymmetrical force
introduction can be brought about, for example, by the position of
bit holder 20 with respect to the rotation direction of the milling
drum. An uneven axial load of this kind results, in the context of
a larger lateral motion (radial motion 82) of support element 70,
in asymmetrical wear on wear surface 31 of bit holder 20. This is
indicated by an orientation of wear surface 31 which is inclined at
a wear angle 84 with respect to a plane proceeding perpendicularly
to longitudinal center axis M. Radial motion 82 is made possible in
a context of insufficient lateral guidance of support element 70.
As a result of this kind of asymmetrical erosion of wear surface
31, support element 70 that guides round-shank bit 60 rests on wear
surface 31 obliquely to longitudinal center axis M. Receiving
orifice 77 is thus not aligned exactly with longitudinal center
axis M of bit receptacle 32. Smooth rotatability of round-shank bit
60 can be impeded or suppressed by this misalignment. Uneven
erosion of wear surface 31 also results in severe longitudinal wear
on holding portion 30.
[0051] FIGS. 7 to 15 are schematic lateral section views each
depicting a detail of a holding portion 30 of bit holder 20 in the
region of centering receptacle 33. Only half of the rotationally
symmetrically embodied holding portions 30, up to longitudinal
center axis M of holding portion 30, is depicted in each case. The
schematic depictions are not accurately to scale.
[0052] In the embodiment shown in FIG. 7, centering surface 33.1 of
centering receptacle 33, oriented obliquely to longitudinal center
axis M, transitions tangentially into the surface of projection 34.
Projection 34 is transitioned at its outer termination in rounded
fashion into wear surface 31 of holding portion 30. Projection 34
is embodied in the form of a ridge. It is arranged surroundingly
with respect to centering receptacle 33. Projection 34 protrudes
beyond wear surface 31. Projection 34 constitutes, at its highest
point with respect to wear surface 31, a maximum point 37. The
transition from centering surface 33.1 into the cylindrical
enveloping surface of bit receptacle 32 forms one end 36 of
centering receptacle 33. A centering height 81 labeled with a
double arrow indicates in the present case the distance, measured
in the direction of longitudinal center axis M, between end 36 of
centering receptacle 33 and maximum point 37 of projection 34.
[0053] Projection 34 has a first radius 86 in a range between 0.5
mm and 6 mm, in the present case of 1.5 mm. The height of
projection 34 with respect to wear surface 31 is preferably in a
range between 0.3 mm and 2 mm, preferably between 0.5 mm and 1.5
mm, in the present case is 1.0 mm. Projection 34 transitions into
wear surface 31 via the rounded region having a second radius 87.
The transition from projection 34 to centering surface 33.1 of
centering receptacle 33 proceeds continuously. Edges between
centering surface 33.1, projection 34, and wear surface 31 are thus
avoided. thereby improving free rotatability of an installed
support element 70 around longitudinal center axis M.
[0054] Projection 34 is shaped onto holding portion 30 in the
context of the manufacture of bit holder 20. When the tool system
is installed, said projection engages into receptacle 75 of support
element 70 as shown in FIG. 5. Inside diameter D.sub.i 85 of bit
receptacle 32 is marked with an arrow.
[0055] According to the present invention, centering height 81 is
designed in such a way that the ratio between inside diameter
D.sub.i 85 of bit receptacle 32 and centering height 81 assumes a
value of less than 8. Centering height 81 is defined by the axial
dimensioning of centering receptacle 33 and of projection 34.
[0056] A ratio of less than 8 between inside diameter D.sub.i 85 of
bit receptacle 32 of bit holder 20 and centering height 81 ensures
good lateral guidance of support element 70 and thus of round-shank
bit 60. In particular, centering height 81 is designed in such a
way that it is greater than axial play 80 of round-shank bit 60 and
thus of support element 70. The dimensioning of centering height 81
as a function of inside diameter D.sub.i 85 of bit receptacle 32
takes into account the greater permissible axial play 80 for larger
tool systems. Sufficient lateral guidance of support element 70,
and thus of round-shank bit 60, is thus ensured regardless of tool
size.
[0057] Good radial guidance of support element 70 is also achieved,
even with a maximum deflection of round-shank bit 60 out of bit
receptacle 32 within the permissible axial play 80, by counterpart
centering surface 74.1, abutting against centering surface 33.1 of
centering receptacle 33, of centering projection 74 of support
element 70. Further lateral guidance of support element 70 is
achieved by way of recess 75 shown in FIG. 5 and projection 34,
engaging thereinto, of bit holder 20. Lateral motions or tumbling
motions of support element 70 can thereby reliably be avoided.
Longitudinal wear on holding portion 30 of bit holder 20 can thus
be considerably reduced. Asymmetrical wear on wear surface 31 in a
context of uneven loading of support element 70, as described with
reference to FIG. 6, can be avoided or at least considerably
minimized. Consistently good rotation of round-shank bit 60 and of
support element 70 is achieved by the absence of an angular offset,
with reference to longitudinal center axis M, of wear surface 31
constituting an abutment surface for support element 70 and thus
for round-shank bit 60.
[0058] Easy rotatability of support element 70 and of round-shank
bit 60 is furthermore obtained by way of the rounded or continuous,
and thus edge-free, transitions between centering surface 33.1,
projection 34, and wear surface 31. Sharp transitions can easily
cause support element 70 to tilt with respect to bit holder 20, and
thereby prevent rotation. This can be avoided by the rounded or
continuous transitions.
[0059] In the exemplifying embodiment of a holding portion 30 shown
in FIG. 8, a guidance groove 35 is shaped into wear surface 31.
Guidance groove 35 surrounds centering receptacle 33 at a distance.
It has a trapezoidal contour having lateral surfaces proceeding
inclinedly with respect to wear surface 31. Projection 34 is
embodied between centering receptacle 33 and guidance groove 35. It
too has a trapezoidal contour. In the exemplifying embodiment
shown, projection 34 terminates in the same plane as wear surface
31 alongside guidance groove 35. Toward longitudinal center axis M,
projection 34 transitions directly into the inclinedly proceeding
centering surface 33.1 of centering receptacle 33. Here and in all
the further embodiments described below, centering receptacle 33 is
terminated by end 36 formed in the transition from centering
surface 33.1 to the enveloping surface of bit receptacle 32.
[0060] A guidance land is shaped onto seating surface 73,
surroundingly with respect to centering projection 74, onto seating
surface 73 of a support element 70 that is not shown in FIG. 8 and
is adapted to the end-face contour of holding portion 30. The
guidance land has a contour complementary to guidance groove 35.
The guidance land therefore engages into the corresponding guidance
groove when the tool system is installed. Further lateral guidance
of support element 70 is thereby achieved. Tumbling motions of
support element 70 can thereby be very largely avoided.
Longitudinal wear on holding portion 30 can be further reduced by
way of guidance groove 35 and a guidance land engaging
thereinto.
[0061] Centering height 81 is measured in the direction of
longitudinal center axis M between end 36 of centering receptacle
33 and the upper surface of projection 34, as depicted by a double
arrow. The ratio between inside diameter D.sub.i 85 of bit
receptacle 32 and centering height 81 is selected to be less than
8, in the present case less than 6.5. Good lateral guidance of the
support element is thereby achieved. With a ratio of less than 6.5,
sufficient lateral guidance is achieved even toward the end of the
service life of support element 70 and of round-shank bit 60, when
axial play 80 of round-shank bit 60 may have become greater as a
result of wear that has already occurred.
[0062] In a departure from the embodiment depicted, the transition
from centering surface 33.1 to projection 34, and/or the transition
from projection 34 to the adjoining lateral surface of guidance
groove 35, and/or the transition from the oppositely located
lateral surface of guidance groove 35 to the adjacent wear surface
31, can be rounded. The transitions from the lateral surfaces to
the groove bottom can also be embodied in rounded fashion. Sharp
edges can thereby be avoided, resulting in improved rotatability of
support element 70.
[0063] With bit holder 20 shown in FIG. 9, a trapezoidal guidance
groove 35 is once again shaped into wear surface 31. A projection
34 shaped on between guidance groove 35 and centering receptacle 33
has a ridge-shaped contour. The radius of projection 34 is selected
so that its surface transitions tangentially into centering surface
33.1 of centering receptacle 33, and oppositely into the adjoining
lateral surface of guidance groove 35. Centering height 81
corresponds to the distance, measured in the direction of
longitudinal center axis M, between end 36 of centering receptacle
33 and maximum point 37 of projection 34. Good lateral guidance of
support element 70 is achieved thanks to the immediately successive
combination of centering recess 33, projection 34, and guidance
groove 35 in conjunction with a seating surface 73, shaped
correspondingly thereto, of a support element 70.
[0064] Wear surface 31 of holding portion 30 shown in FIG. 10
transitions directly into centering surface 33.1 of centering
receptacle 33. In the outer region of wear surface 31, a
ridge-shaped projection 34 is shaped thereonto. Centering height 81
is measured along longitudinal center axis M between end 36 of
centering receptacle 33 and maximum point 37 of projection 34. The
arrangement of projection 34 comparatively far outward on holding
portion 30 results in particularly good stabilization of the
rotational motion of an abutting support element 70 embodied
correspondingly thereto.
[0065] FIG. 11 shows a holding projection 30 having a surface that
faces toward a support element 70 (not shown) and is embodied in
multiple steps. Centering surface 33.1 transitions into an abutment
surface 38 arranged transversely to longitudinal center axis M, in
particular perpendicularly to longitudinal center axis M. Adjoining
abutment surface 38 is a projection 34 that protrudes beyond
abutment surface 38. The surface of the ridge-shaped projection 34
transitions tangentially into the adjoining lateral surface of a
trapezoidally embodied guidance groove 35. Wear surface 31 is
arranged surroundingly with respect to the guidance groove.
Abutment surface 38, maximum point 37 of projection 34, the groove
bottom of guidance groove 35, and wear surface 31 are arranged on
different planes along longitudinal center axis M. Measured
parallel to longitudinal center axis M, maximum point 37 is spaced
the farthest from end 36 of centering receptacle 33, followed by
abutment surface 38, wear surface 31, and the groove bottom of
guidance groove 35. Thanks to this profile, implemented over
different planes, of the end surface of holding portion 30, very
good lateral guidance of a support element 70 embodied
correspondingly thereto is achieved. Both result in decreased wear
on holding portion 30 and thus on bit holder 20.
[0066] In the exemplifying embodiment of bit holder 20 shown in
FIG. 12, projections 34 arranged concentrically with one another
are shaped onto holding portion 30 around centering receptacle 33.
A wave-shaped contour, whose surface represents wear surface 31, is
thereby formed. Centering height 81 is measured between end 36 of
centering receptacle 33 and maximum point 37 of the innermost
projection 34. When neighboring projections 34 have different
heights, centering height 81 is preferably determined at maximum
point 37 of the highest projection 34. Good rotatability of a
corresponding support element 70 is ensured by projections 34
arranged surroundingly with respect to centering receptacle 33. As
a result of the wave-shaped contour, the surface of holding portion
30 projected in an axial direction remains equivalent to a flat
plane, so that the axial supporting effect is maintained. The
radially effective area is considerably enlarged by the lateral
flanks of projections 34. Transverse forces can thereby be better
absorbed. The contact area between a support element 70 and holding
portion 30 of bit holder 20 is enlarged by the wave shape. This
leads to reduced wear on bit holder 20 and improved rotatability of
support element 70 and thus of round-shank bit 60.
[0067] FIG. 13 shows a detail of a bit holder 20 having a flat wear
surface 31 onto which two ridge-shaped projections 34, proceeding
concentrically with one another, are shaped. Good rotatability and
good lateral stabilization are achieved with this arrangement as
well.
[0068] Bit holder 20 depicted in FIG. 14 has a wear surface 31 that
proceeds linearly but is oriented obliquely to longitudinal center
axis M. Maximum point 37 is embodied in the rounded transition
region from centering surface 33.1 into wear surface 31. Because of
their orientation obliquely to longitudinal center axis M, both
centering surface 33.1 and wear surface 31 have a radially
stabilizing effect on the position of a support element 70 that is
adapted to wear surface 31 in terms of the contour of its seating
surface 73. Centering height 81 is measured, in the direction of
longitudinal center axis M, from end 36 of centering receptacle 33
to maximum point 37 at the transition from centering surface 33.1
to wear surface 31.
[0069] With bit holder 20 shown in FIG. 15, wear surface 31
proceeds obliquely to longitudinal center axis M of holding portion
30. The greatest distance, measured in the direction of
longitudinal center axis M, between end 36 of centering receptacle
33 and wear surface 31 is obtained at the outer rim of holding
portion 30, so that that distance constitutes centering height 81.
In this exemplifying embodiment as well, both centering surface
33.1 and wear surface 31 oriented obliquely to longitudinal center
axis M have a radially stabilizing effect on a correspondingly
shaped abutting support element 70.
[0070] In summary, it can be stated that thanks to the embodiment
according to the present invention of holding portion 30 of bit
holder 20, in which the ratio between inside diameter D.sub.i 85 of
bit receptacle 32 and centering height 81 is less than 8, and/or in
which centering height 81 is greater than an axial play 80 of a
round-shank bit 60 installed in bit holder 20, longitudinal wear on
holding portion 30 in relation to the operating time of the tool
system can be considerably reduced. Tilting of round-shank bit 60
upon initial operation can be almost avoided thanks to the improved
and more-stable engagement of projection(s) 34 into recesses 75 of
a support element 70 which correspond thereto. Longitudinal wear on
holding portion 30 is thereby evened out. The bit shank, and bit
receptacle 32, are better protected from contaminants by the
enhanced sealing effect of the resting surface between support
element 70 and holding portion 30. This too results in considerably
reduced wear on bit holder 20 in the region of its holding portion
30. Premature wear on or fatigue breakage of insertion projection
40 of bit holder 20 can be avoided by embodying bearing surfaces
23, 24 to abut against correspondingly embodied support surfaces
16.1, 16.2 of base mount 10. The life expectancy of bit holder 20
as an assembly can thus be considerably extended by the features.
This results in reduced costs for maintenance and replacement
parts.
* * * * *