Apparatus for releasably coupling grinding tools to rotary spindles

Apparatus for coupling a rotary grinding tool to a rotary spindle has a long centering cone at the front end of the spindle for entry into a complementary conical hole in the main portion of a hub which separably holds the tool. The spindle transmits torque to the hub by means of two male torque transmitting elements provided on an axial extension of the hub and extending into complementary recesses provided on a ring-shaped member at the smaller-diameter end of the cone. The tool is held in a predetermined axial position by an end face of the extension which abuts an end face of the cone. A package of springs is installed in the cone to normally bias the extension of the hub axially of and away from the spindle so as to facilitate separation of the tool from the spindle by means of an automatic tool changer. The spring surrounds the shank of a screw or bolt which separably secures the extension of the hub to the cone of the spindle.

BACKGROUND OF THE INVENTION 
The invention relates to an apparatus for releasably coupling rotary 
material removing tools to rotary driving elements, particularly for 
separably securing grinding wheels or analogous tools to rotary spindles 
in grinding machines. More particularly, the invention relates to 
improvements in coupling apparatus of the type wherein the rotary driving 
element (hereinafter called spindle for short) includes or carries an 
elongated cone which is receivable in a complementary hole or bore of a 
flange or hub which is preferably separably connected to and carries the 
material removing tool. The apparatus of the present invention can be 
utilized to couple a variety of rotary material removing tools, especially 
grinding wheels, dressing wheels, profiling rolls and the like. 
It is customary to provide the spindle of a grinding machine with an 
elongated cone which can support and transmit torque to a material 
removing tool (hereinafter called grinding wheel or tool for short). As a 
rule, the cone is rather long so as to ensure that its external surface is 
held in self-locking engagement with the surface surrounding the conical 
hole or bore of the hub. A drawback of such conventional coupling 
apparatus is that the axial position of the hub relative to the cone 
cannot be selected and maintained with a desired degree of accuracy. 
Furthermore, the self-locking action between the cone and the hub for a 
grinding wheel or the like exhibits the drawback that the apparatus cannot 
be actuated by automatic grinding wheel changers. 
Attempts to overcome the drawbacks of such conventional apparatus include 
the utilization of so-called short cones of the type disclosed, for 
example, in commonly owned German published application No. 34 19 397 and 
in German Pat. No. 34 03 3661. The utilization of a relatively short cone 
reduces the likelihood of self-locking and thus simplifies and facilitates 
the mounting of the hub on as well as separation of the hub from the cone 
on the spindle. The cone takes up radial stresses, i.e. it serves to 
center the hub on the spindle. The means for transmitting torque from the 
spindle to the tool includes end faces at one axial end of the spindle, 
and such end faces further serve to ensure that the hub is held in a 
predetermined axial position with reference to the cone. A drawback of 
coupling apparatus which utilize relatively short cones is that they 
cannot be used in connection with the mounting of and transmission of 
torque to relatively large and heavy grinding and like material removing 
tools. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of the invention is to provide a coupling apparatus which employs 
a relatively long cone but is nevertheless suitable for actuation by 
automatic tool changing devices. 
Another object of the invention is to provide an apparatus which can be 
utilized to separably secure the hubs of existing grinding and like 
material removing tools to the relatively long cone of a spindle or a like 
driving element. 
A further object of the invention is to provide an apparatus which is 
simple, compact and relatively inexpensive and can be actuated by a 
variety of existing tool changing systems. 
Still another object of the invention is to provide an apparatus wherein 
the hub automatically moves axially of and in a direction away from the 
cone as soon as the positive locking connection between the hub and the 
cone is relaxed or terminated. 
The improved apparatus is used to releasably couple a material removing 
tool, particularly a grinding wheel, to a rotary spindle or a like driving 
element. The apparatus comprises means for centering the tool in the 
spindle, including a hub which is connectable with the tool or is an 
integral part of the tool and has a conical hole, and a complementary cone 
provided on the spindle and extending into the hole; means for locating 
the tool in a predetermined axial position with reference to the spindle 
including abutment means provided on the hub and on the cone; and means 
for transmitting torque from the spindle to the tool including 
complementary torque transmitting elements which are provided on the cone 
and on the hub at one axial end of the cone. 
The abutment means preferably comprises a first end face at one axial end 
of the cone and a second end face 4 adjacent to the first end face and 
provided on the hub. The hub preferably comprises a main portion which is 
connectable with the tool, an extension, and means for fastening the 
extension to the main portion. The second end face is preferably provided 
on the extension of the hub. The hub can further comprise a substantially 
ring-shaped shim of predetermined thickness which is interposed between 
the main portion and the extension. 
The torque transmitting elements preferably comprise at least one male 
torque transmitting element on the end face of the extension and at least 
one complementary female torque transmitting element on the end face of 
the cone. The positions of the male and female torque transmitting 
elements can be interchanged. 
The apparatus preferably further comprises means for urging the hub axially 
of and away from the cone. The hub is releasably secured to the cone by a 
threaded fastener having a shank which is coaxial with the hub and with 
the cone. The urging means preferably comprises at least one resilient 
element which serves to bias the hub axially and away from the cone. The 
resilient element can include at least one annular spring (for example a 
package of annular dished springs) surrounding the shank. The urging means 
preferably further comprises an annular plunger which surrounds the shank 
and abuts the hub. The resilient element reacts against the cone and bears 
against the plunger. The plunger is preferably reciprocable in an axial 
passage of the main portion of the hub and bears against the extension 
under the bias of the resilient element. This renders it possible to move 
the hub axially of and away from the cone as soon as the threaded fastener 
which connects the hub to the cone is rotated in a direction to loosen the 
connection between the hub and the cone. 
The main portion of the hub is preferably provided with means (such as one 
or more facets, one or more threaded bores or the like) for facilitating 
the application to the main portion of a force which prevents rotation of 
the main portion relative to the cone during rotation of the fastener in a 
direction to secure the extension to or to allow for separation of the 
extension from the main portion of the hub. 
The novel features which are considered as characteristic of the invention 
are set forth in particular in the appended claims. The improved apparatus 
itself, however, both as to its construction and its mode of operation, 
together with additional features and advantages thereof, will be best 
understood upon perusal of the following detailed description of certain 
specific embodiments with reference to the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 show an apparatus which serves to separably couple a material 
removing tool 8 (herein shown as a rotary grinding wheel) to a driving 
element 1 in the form of a rotary spindle which is mounted in a spindle 
carrier 3 with the interposition of one or more antifriction ball, roller 
or needle bearings 2. The front end of the spindle carrier 3 is sealed by 
a ring-shaped sealing element 4. 
The means for centering the tool 8 on the spindle 1 comprises an elongated 
centering cone 6 which is provided at the front axial end of the spindle 3 
and is received in a complementary conical hole or bore 11 provided in the 
main portion of a hub 7 which separably carries the grinding tool 8. The 
main portion of the hub 7 comprises two coaxial ring-shaped sections 7a 
and 7b which are separably held together by threaded fasteners 9. The 
flanges of the sections 7a and 7b are disposed at opposite axial ends of 
the tool 8. The conical hole 11 is provided in the section 7b. The lengths 
of the cone 6 and of the hole 11 are preferably selected or can be 
selected in such a way that the external surface of the cone is in 
self-locking engagement with the surface surrounding the hole 11. This 
means that a relatively large force is necessary to separate the hub 7 
from the cone 6. 
In order to enable an automatic tool changing system to remove the tool 8 
from or to attach the tool to the spindle 1, the cone 6 and the surface 
surrounding the hole 11 merely perform a centering action rather than 
transmitting torque between the tool and the spindle and/or ensuring that 
the tool is held in an optimum axial position with reference to the 
spindle 1. 
The means for transmitting torque from the spindle 1 to the tool 8 
comprises a ring-shaped member 13 which projects beyond the end face 12 of 
the cone 6 and has two female torque transmitting elements in the forms of 
recesses 14a, 14b (FIG. 2) complementary to and receiving male torque 
transmitting elements 16a, 16b provided on an extension 18 of the hub 7. 
The extension 18 is coaxially but separably affixed to the section 7b of 
the main portion of the hub 7 by one or more threaded fasteners in the 
form of bolts or screws 17. 
The means for maintaining the tool 8 in a predetermined axial position with 
reference to the spindle 1 comprises an end face 19 which is provided on 
the member 13 of the cone 16 and an adjacent abutting end face 21 at the 
inner side of the extension 18. The end face 19 includes two arcuate 
sections provided on two arcuate portions 22a, 22b which form part of the 
member 13 and alternate with the female torque transmitting elements or 
recesses 14a, 14b. The end face 21 of the extension 18 has two arcuate 
sections which alternate with the male torque transmitting elements 16a 
and 16b. The two sections of the end face 21 are located at the right-hand 
axial ends of the elements 16a, 16b as seen in FIG. 1. The plane in which 
the end faces 19, 21 abut when the apparatus is properly assembled is 
indicated in FIG. 1 by a broken line. 
The illustrated coupling apparatus further comprises a ring-shaped shim 23 
which is disposed between the main portion 7a, 7b of the hub 7 and the 
extension 18. The thickness of the shim 23 depends upon the width of the 
clearance or gap between the extension 18 and the main portion of the hub 
7. The width of the gap depends on the manufacturing tolerances, 
particularly upon the tolerances of machining the cone 6 and the surface 
surrounding the conical hole 11 in the main portion of the hub 7. The 
means for releasably securing the extension 18 to the section 7b of the 
hub 7 comprises a threaded fastener 24 having an externally threaded shank 
29 which extends into a tapped axial bore of the cone 6. 
The apparatus further comprises means 26 for urging the hub 7 axially of 
and away from the cone 6 so as to facilitate separation of the tool 8 from 
the spindle 1 in response to rotation of the fastener 24 in a direction to 
permit the extension 18 to move axially of and away from the adjacent 
smaller-diameter end portion of the cone 6. Such tendency of the hub 7 to 
move axially of and away from the spindle 1 is particularly desirable when 
the apparatus is to be manipulated by an automatic tool changer. The 
urging means 26 is installed in an axial passage at the smaller-diameter 
end of the cone 6 and comprises a resilient element here shown as 
including a package of annular dished springs 28, and a plunger 27 which 
is an annulus surrounding the shank 29 and being reciprocable in the 
aforementioned axial passage of the cone 6. When the fastener 24 is 
rotated in a direction to permit a movement of the extension 18 axially of 
and away from the cone 6, the resilient element 28 dissipates energy and 
pushes the plunger 27 in a direction to the right, as seen in FIG. 1, so 
that the plunger 27 extends partially beyond the smaller-diameter end of 
the cone 6 and pushes the entire hub 7 axially of and away from the 
spindle 1. The means for preventing complete expulsion of the plunger 27 
from the passage in the cone 6 comprises a resilient ring 31 which is 
received in a circumferential groove 32 of the plunger 27 and is in 
frictional engagement with the surface surrounding the passage of the cone 
6. The frictional engagement between the ring 31 and the internal surface 
of the cone 6 is not sufficient to prevent the springs 28 from dissipating 
energy and moving the extension 18 axially of and away from the cone 6 in 
response to a loosening of the connection between the extension 18 and the 
cone, i.e., in response to rotation of the fastener 24 in a direction to 
permit a movement of the extension 18 and main portion 7a, 7b of the hub 7 
away from the spindle 1. When the fastener 24 is tightened so as to 
properly hold the tool 8 in a predetermined axial position with reference 
to the spindle 1, the urging means 26 acts not unlike a resilient washer 
for the fastener 24 and reduces the likelihood of accidental angular 
displacement of the fastener relative to the extension 18. 
The extension 18 is further provided with means for facilitating the 
application of a force in order to hold the hub 7 against rotation with 
the fastener 24 when the fastener is rotated in a direction to secure the 
hub 7 or to permit disengagement of the hub from the spindle 1. The 
facilitating means comprises one or more recesses 33 which are provided in 
the periphery of the extension 18 and can receive a locking bolt or a like 
element which holds the extension 18 (and hence the entire hub 7) against 
rotation with the fastener 24 when the latter is engaged by a wrench (not 
shown) to receive torque in a clockwise or in a counterclockwise 
direction. To this end, the exposed end portion of the fastener 24 
comprises a hexagonal component 37 which can be engaged by the 
aforementioned wrench. 
The extension 18 is further provided with one or more external facets 34 or 
like configurations which enable the aforementioned automatic tool changer 
to engage and move the extension (and hence the entire hub 7 and the tool 
8) axially of the spindle 1. The exposed end portion of the fastener 24 is 
provided with a circumferential groove 36 which is designed to receive a 
portion of the automatic tool changer. This enables the tool changer to 
simultaneously move the tool 8 and the hub 7 (inclusive of the extension 
18) axially of toward and away from the spindle 1. 
An important advantage of the improved coupling apparatus is that it 
enables an automatic tool changer to manipulate the tool 8 regardless of 
the fact that the spindle 1 is or can be provided with a so-called long 
cone 6. Long cones are particularly desirable when the spindle 1 is to 
carry one or more relatively large and heavy grinding or other material 
removing tools. 
The apparatus can be furnished with a full set of shims 23 of different 
thicknesses so as to make sure that a shim of proper thickness can be 
selected in order to account for the width of the gap between the main 
portion of the hub 7 and its extension 18. The dimensions of the gap can 
be readily ascertained prior to selection of the appropriate shim. 
A further important advantage of the improved apparatus is that the urging 
means 26 facilitates separation of the tool 8 from the spindle 1 which is 
especially important if the apparatus is to be manipulated by an automatic 
tool changer. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic and specific aspects of our contribution to 
the art and, therefore, such adaptations should and are intended to be 
comprehended within the meaning and range of equivalence of the appended 
claims.