GB2127333A - Tool and toolholder couplings in machine tools - Google Patents

Abstract

A coupling 46 has a portion with teeth 76 associated with a tool or tool holder 40 and a portion with teeth 70 associated with a spindle 42 of a machine tool 44. The coupling 46 provides for self-centering and has substantially zero backlash when utilised with the power driven spindle 42. Each coupling portion may be integrally formed with the machine tool and tool or tool holder, respectively, or formed as part of an adapter assembly. The spindle 42 may be replaced by a drive ram or multi-sided turret (not shown). The teeth 70 and 76 are curved and mirror images of one another. <IMAGE>

Description

SPECIFICATION Couplings facilitating releasable attachment of tools and tool holders to machine tools Machine tools are used for precision machining operations, and as is the tendency in many industries, are becoming more frequently computer controlled. The potential for high speed machining as well as high speed interchange of tools is a very important objective. To enable a plurality of machine tools each with a multiplicity of tools associated therewith to have high speed interchangeability, by enabling these same machine tools to utilise a common supply of tools and tool holders having standardised couplings, would provide substantial savings in time and money.

Most machine tools are of the kind in which the tools and tool holders are mounted on power driven spindles. However, it should be noted that it is known to mount tools and tool holders on power driven rams where the tool is non-rotatable. It is also known to mount tools and tool holders on multisided turrets wherein a single tool at a time is presented to a rotating workpiece for work thereon.

All of these kinds of machine tools are designed to accommodate shank-type tools or tool holders, i.e.

tools or tool holders including a shank of the kind commonly known as V-flange, Morris taper, straight shank, etc.

Tools and tool holders utilising a shank have the obvious disadvantage of being bulky as well as creating problems of interchangeability between machine tools which cannot all accept that particular configuration or size of shank. An example of this is where a power driven spindle of one machine tool has been adapted to accommodate a shank-type tool holder of a particular size while other machine tools positioned therearound have been adapted to accommodate tool holders of other configurations or sizes. Here it is evident that each machine tool in this situation would, of necessity, have its own supply of tools or tool holders that are of the particular configuration and size that each of the machine tools has been adapted to accommodate.

Accordingly, a numerically controlled machine tool with a storage caddy of tools and tool holders, usually ranging from 30 to 50 tools or tools with their tool holders which has a robot associated therewith for accommodating changing of the tools, will be precluded from sharing those tools with other machine tools which have been adapted to accommodate tools or tool holders with different shank sizes or configurations. Thus, it is seen that when a machine tool which accommodates shanks of a particular size is juxtaposed a machine tool which accommodates shanks of a different size it is readily apparent that they must have their own separate supplies of tools and tool holders.

Another distinct problem with machine tools hav ing a power driven spindle which is designed to accommodate a shank-type tool or tool holder is that the design of the spindle is compromised in order to be able to provide clearance for the shank. An example of such a compromise is seen in the oversizing of the bearing at the end of the spindle which must be made large enough to support the spindle and also permit the shank to pass therethrough. Thus any of the inherent problems of an oversized bearing will be found in a spindle of this type. A significant problem attributable to a very large bearing used with a power driven spindle is that the maximum speed at which the spindle can be driven for long periods of time using a predetermined amount of horse power is significantly less than for a spindle which employs a smaller bearing using the same predetermined amount of horsepower.

A common problem which has been attempted to be overcome in many ways by machine tool operators and manufacturers, is the inherent problem of a shank seizing within the bore in which it is fitted.

Normally some type of a blow or extreme amount of pressure is required to free the shank from within the accommodating bore. A tool or tool holder subjected to repeated seizing within an accommodating bore and the stresses created by the various methods of extraction often show excessive wear or damage.

Yet another problem with a shank-type tool holder is that when the associated tool is to be adjusted relatively to the tool holders a particular fixture is needed for supporting the tool holder in a manner such that a precise measurement of the extension of the tool therefrom can be made. Because of the need for a special fixture it is not unknown for the operator of the machine tool to attempt to make an adjustment by simply standing the shank-type tool holder on its smaller end and attempting the adjustment by measuring up from the surface on which the smaller end is resting. In so doing the tool holder may be knocked over resulting in chipping of the tool.

Clearly this is an extreme economic waste when considering the substantial expense of tools used in virtually all machining operations.

Accordingly it was the general object of the inventors to provide a quick change coupling which avoids some if not all of the problems of the prior art.

In accordance with one aspect of the present invention, a combination comprises a machine tool, a tool or tool holder for use with said machine tool and coupling means for attaching said tool or tool holder to support means on said machine tool, said coupling means having a first portion associated with said tool or tool holder and a second portion associated with said support means, said first and second portions including generally radially disposed means capable of directly intermeshing in a disengageable manner for self-centering of said tool or tool holder relatively to said support means.

Other aspects of the present invention relate to the structure of preferred tools and tool holders as well as to methods of adapting machine tools and methods of changing tools or tool holders as set out in the accompanying claims.

The first portion of the coupling means may be integral with the tool or tool holder, and the second portion of the coupling means may be integral with the support means, but alternatively the coupling means may form part of an adapter assembly including means for attaching said first portion of said coupling means to said tool or tool holder and means for attaching said second portion of said coupling means to said support means.

Preferably, the generally radially disposed means includes a plurality of generally radially extending teeth, which in turn are preferably curved teeth, each of the teeth having an inner concave and and outer convex tooth face with each tooth on the first or second portion being so configured that any contact point along both its inner concave and outer convex faces has a spiral angle and a pressure angle which are equal to those of its corrsponding contact point along the respective outer convex and inner concave faces of the other portion.

The width of each curved tooth may vary from its innermost portion to its outermost portion, and the teeth may be arranged in one or more concentric bands, and a root may be formed between each adjacent pair of the teeth on the first and second portions for receiving debris.

Preferably, the support means is a power driven spindle, securing means are provided for drawing said first portion axially into engagement with said second portion associated with said spindle thereby substantially simultaneously self-centering said tool or tool holder relatively to said spindle and establishing a rigid drive for said tool ortool holder through said coupling means, and said securing means is in the form of a draw bar having a threaded end for engagement in a threaded bore formed in said tool or tool holder.

It will be appreciated that advantages of the present invention, particularly the preferred embodiments thereof, are that a quick change coupling is provided which is relatively simple and inexpensive both in manufacture and use, and yet is highly reliable over a long service life of multiple reuses.

The tool and tool holder may be readily engageable and disengageable from the support means without the necessity of external rather than internal forces being applied thereto. The tool or tool holder may accommodate mechanical means for drawing it proximate the support means, may have a provision for accommodating debris which may have accumulated in the coupling, and may accommodate torque applied in either direction.

Another advantage is the provision of a quick change coupling and a method of utilising the coupling to standardize machine tools and thereby enable a plurality of machine tools to be supplied with tools from a common storage facility wherein each of the tools stored therein includes a universal coupling portion. A further advantage is the provision of a coupling wherein each of the coupling portions is of a standardised configuration and wherein the radial extent of a coupling portion is insignificant as long as there are portions of the coupling which mate.

Yet another advantage is the provision of a tool or tool holder which may include means for accommodating the robotics of a quick change system such thatthetool ortool holder can be readily moved back and forth between a storage facility and the support means.

Important advantages of the present invention include providing a tool or tool holder which may be repeatedly coupled and uncoupled from support therefor without affecting the accuracy and efficacy of the coupling; ensuring that the accuracy of the alignment of the tool or tool holder be maintained during its multiple reuses; minimizing run out and precession of the tool relative to a spindle when the coupling is used with a rotating spindle; and ensur ing substantially zero backlash when torque is applied thereto.

Several embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a partial sectional view of a portion of a prior art machine tool spindle and tool holder; Figure 2 is a partial sectional view of a portion of a machine tool spindle and a tool holder embodying the present invention; Figure 3 is a view taken in the direction of the arrows 3-3 in Figure 2 showing the coupling portion associated with the spindle; Figure 4 is a view taken in the direction of the arrows 4-4 in Figure 2 showing the coupling portion associated with the tool holder; Figure 5 is a side view of a cutting tool embodying the present invention; and Figure 6 is a partial view in cross-section showing the intermeshing of the teeth of the coupling portions shown in Figures 3 and 4.

Referring now to the drawings and initially to Figure 1 there is shown a common shank-type tool holder 12, in the industry referred to as a V-flange holder, and a power driven spindle 14 of a machine tool 16 which has been adapted to accommodate the shank-type tool holder 12. This is one of the preferred type tool holders in the industry and includes a flange 18 having a substantially V-shaped groove 20 therein for engagement by the robotics associated with the machine tool 16. The robotics are particularly adapted for extracting the tool holder 12 from the end of the power driven spindle 14 and moving the tool holder 12 back and forth between a storage position (not shown) and the end of the spindle. As seen in Figure 1 the prior art tool holder 12 includes an end 22 for accommodating a tool (not shown) and an end 24 including a tapered shank 26.

In the free end of the tapered shank 26 there is shown a threaded bore 28 which is engageable by a draw bar 30 of the machine tool 16 for axially drawing and retaining the tool holder 12 against the end of the spindle 14. The transmission of the torque from the power driven spindle 14 to the tool holder 12 is accomplished through a pair of keys (not shown) which mechanically engage the flange 20 of the tool holder 12 with the spindle 14. This type of engagement, i.e. keys and slots (not shown), which is the common type of interconnecting for this type of tool holder, permits substantial amounts of backlash of the tool holder 12 relative to the spindle 14. When a tool holder of the type shown in Figure 1 is to be utilised with a machine tool it is necessary for the spindle 14to be modified to include frustoconical bore 32 which is of a particular dimension to closely accommodate the particular dimension of the shank 26 of the shank-type tool holder 12. Due to the fact that the end of the power driven spindle 14 is adapted to accommodate the shank 26 of a shanktype tool holder 12, it should be noted, that the size of the bearing 34 and its positioning is compromised in that the bearing 34 must be of a diameter to permit the shank 26 of the tool holder 12 to pass therethrough. As will be discussed later, there are advantages to controlling the size and position of the bearing.

Referring now to Figure 2, there is depicted a tool holder 40 shown attached to a power driven spindle 42 of a machine tool 44 through a coupling 46 embodying concepts of the instant invention. The tool holder 40 has a longitudinal axis 48, at one end 50 of which there is a bore 52 which is shown for illustrative purposes only with the knowledge that any of the known type tool attaching mechanisms could be used in its stead, and at the other end of which there is a perpendicularly disposed first portion 54 of the coupling 46. The bore 52 includes locking screws (not shown) for securing the shank of a cutting tool (not shown) relative thereto. Extending coaxially with the longitudinal axis 48 of the tool holder 40 is a threaded bore 54 for receiving the threaded end 56 of the draw bar 58 of the machine tool 44, the necessity of which will be explained hereinafter.It should also be noted that the particular draw bar 58 and the means for attaching it to the tool holder 40, e.g. the threaded bore, is also shown for illustrative purposes only and it should be understood that any of the common attaching devices used for securing a draw bar to a tool or tool holder may be incorporated herein. Included in the tool holder 40 is a common flange 60 having a V-shaped groove 62 therein enabling engagement thereof by the robotics associated with the machine tool 44 for affecting movement of the tool holder 40 to and from a storage area (not shown) and the end of the spindle 42. As seen in Figure 2, the bearing 64 is substantially smaller in its overall diameter when compared to the bearing 34 of the prior art device 12.

The intention is to show how significantly the sizes of the bearings 34 and 64 may vary when there is a predetermined amount of horse power and an identical cutting tool (not shown) used as constants.

Thus, it will be appreciated that no special provisions within the spindle 42 are necessary other than for accommodating the draw bar 58. It should be noted that it is contemplated herein that a common bayonet-type mount as well as other mechanical mechanisms may be employed herein for securing the tool holder proximate the end of the spindle thereby eliminating the need for a draw bar. In this latter instance the bearing 64 may be even smaller.

As is known in the arts, a smaller bearing may be run at higher speeds than a larger bearing of the same material with less heat build-up, etc.

Referring now to Figures 3 and 4, the two complimentary portions 66,68 of the coupling 46 of the instant invention are shown therein. While it should be understood that a particular tooth form is disclosed and discussed herein, there are other tooth forms which will accomplish the objectives of the instant invention. As seen in Figure 3, the portion 66 of the coupling 46 associated with the face of the spindle 42 includes curved teeth 70 extending from the outer periphery inwardly. The teeth 70 are spaced equidistantly or in a pattern completely around (not shown) the circumference of the coupling portion 66. Each of the curved teeth 70 has two lateral faces, a concave or inward face 72 and a convex or outward face 74.For this particular tooth configuration there is contact point P1 on either of the faces, there is an associated spiral angle A1 and an associated pressure angle B1 (see Figure 6).

Referring to Figure 4, it is seen therein that the generated tooth pattern is a mirror image of the tooth pattern as depicted in Figure 3. Each tooth 76 of coupling portion 68 has a contact point P2 along each concave face 78 or convex face 80 thereof, and a spiral angle A2 and a pressure angle B2 (see Figure 6) that is equal to the angles Ar and B1 for the associated contact point P1 of each tooth 70 of the coupling portion 66 depicted in Figure 3. It should be noted at this point that while other tooth configurations are contemplated herein it is also contemplated that the generated pattern of teeth need not be continuous in its extent around the faces of the coupling portions.Again it should be noted that reference made to teeth are with the understanding that any radially disposed means which will accomplish the objectives of the instant invention are intended to be contemplated hereby.

Referring again to Figures 3 and 4, it will be seen that there are generally radially disposed teeth 70 and 76 which constantly increase in dimension as they radiate outwardly. Accordingly, a coupling portion (not shown) of a particular diameter may accommodate a second coupling portion (not shown) of a different diameter as long as they include tooth means which will engage at a diameter common to both portions. Thus a spindle having a first portion associated therewith, which is of a first diameter, may accommodate tools or tool holders to be driven thereby, which are of a different diameter.

Ideally, the diameter of a coupling portion associated with the spindle is larger than the diameter of the coupling portion associated with the cutting tool, in that it may be considered to be not necessarily advantageous to have a cutting tool driven by a coupling portion associated therewith which has a diameter substantially larger than the diameter of the coupling portion associated with the spindle. It should be understood that the torque being transmitted can be controlled by the speed of the spindle and the amount of engagement of the cutting tool with a substrate.

Referring to Figure 6, there is depicted the intermeshing of the teeth 70 and 76 of two coupling portions 66 and 68 and a showing of a clearance area 82 in the root of each tooth 70 and 76 to accommodate debris which may have accumulated on the face of the teeth. Bits of debris which may inhibit full engagement of the teeth 70 and 76 can thusly be wiped into the clearance area 82 by the teeth as they are intermeshed. It should be understood that the clearance area 82 is not critical to the concept of the coupling or uncoupling and may be omitted in certain applications. The inclusion of an open clearance area 82 as depicted in Figure 6 would not necessarily be desirable when a coolant flow problem would arise because of intercommunication of the clearance areas 82 with porting (not shown) within the spindle and tool or tool holder for the coolant flow.

As seen in Figure 5, there is shown a cutting tool 84 having one portion 68 of the coupling 46 formed as an integral part thereof. Included as an integral part of the cutting tool are those features necessary to facilitate engagement by the robotics (not shown) associated with the machine tool for movement of the cutting tool 84 to and from a storage facility (not shown) and the spindle 42 of the machine tool 44. As indicated by the distance D, it should be readily apparent that the overall length dimension of this unitary device 84 may be substantially less than that of a tool holder and cutting tool combination which of necessity includes the structure for attachment of the cutting tool to a holder.Accordingly, by eliminating the bore portion of a holder and the structure attendant thereto and the portion of a cutting tool necessary to cooperate with the bore portion (not shown), the overall length dimension D of the integrally formed cutting tool may be substantially decreased. The apparent advantage of such a configuration is that a greater degree of flexibility in the size of articles being machined is increased when the area in which the cutting tool is being used is restricted. When reference is made herein to cutting tools it is to be understood that any of the common types of cutting tools is intended to be included, e.g., insertable blade type cutters, carbide tip cutters, etc.

As described, the coupling portions 66 and 68, depicted in Figure 3 and 4, may be formed integrally as part of the end of the power driven spindle 42 or tool support (not shown) and the tool 84 or tool holder 40, respectively. Also, it should be understood, that each of the portions 66 and 68 of the coupling 46 may be separately formed and subsequently attached to the spindle 42 or tool support (not shown) and tool 84 or tool holder 40, respectively. When forming the coupling portions 66 and 68 as separate pieces it is then incumbent that each of the portions be attached so as to be centered relative to the rotational axis of the spindle 42 or tool support (not shown) and the tool 84 or tool holder 40, respectively. As will be appreciated by those skilled in the art, the attachment of a separate pieces may be accomplished by any suitable means (not shown), e.g., bolts, welding, etc.Accordingly, it should be readily apparent that by forming the coupling portions as separate pieces an adaptor has been formulated.

While a ring of substantially radially disposed teeth has been shown on each of the coupling portions 66 and 68, it is contemplated that there may be a plurality of bands (not shown) of teeth on each portion of the coupling. Each of these bands may be disposed radially relative to the other bands. When bands of teeth of a generally arcuate configuration are utilized, each band may be formed so as to have the teeth therein curved in a predetermined direction. By including bands of teeth which extend in different predetermined directions at different radial distances, it can be seen that tool holders of different diameters may be selectively designed to engage, in a selective manner, a particular band.In the alternative, engagement of a particular tool or tool holder may be precluded due to an inability of the coupling portion thereon to engage with the coupling portion on the support or spindle. Thus, selectively as to which cutting tools may be accommodated by a particular spindle may be controlled. In a situation were right hand and left hand cutting tools are employed it is obviously undesirable for an incorrect cutting tool to be engaged due to the fact that when a cutter is run backward high stresses and friction are encountered and the cutter may be destroyed.

A distinct advantage to using a tool 84 or tool holder 40 of the type disclosed herein, is that the user may advantageously accomplish measurement of the axial extension of the cutting tool by simply setting the tool 84 or tool holder 40 on a planar surface with the teeth 76 of the coupling portion resting there against and measuring from the planar surface to that point of the cutting tool furthest from the support surface.

The coupling as disclosed as part of this invention has as one of its principal advantages the standardization of machine tools which have been particularly adapted to accommodate shanktype tool holders.

Commonly, machine tools which have been adapted for shank-type tools and tool holders are no longer universal due to their being adapted to receive a particular size of shank. A secondary advantage when using the coupling of the instant invention is that the machine tool and/or robotics which service the machine tool need no longer have the capability of applying the substantial amount of force necessary, either by hammering or otherwise, to uncouple a seized shank-type tool or tool holder When standardization of variously adapted machine tools is desired the modification of the end of the power driven spindle or support may be accomplished by either the machining of the complimentary coupling portion therein or the attachment of an adaptor having the complimentary tooth portion as part thereof.Thus, a common tool caddy having a multiplicity of tools or tool holders may be established which, in the case of numerically controlled robotically fed machine tools, will eliminate the need for separate tool caddies having tools or tool holders which are particularly adapted for each machine.

As is understood by those familiar with machine tools, the maximum speed with which a machine tool operates is limited by the maximum speed at which the bearing within the spindle may operate.

Clearly, a machine tool which is numerically controlled and capable of operating for many hours and sometimes days at a time without operator assistance, can potentially have a heat build-up within the bearing if the spindle were to be driven at too high a speed. Knowing that the bearing is the limiting factor in the speed with which a machine tool can operate, it is then understood that a particular machine tool which is adapted to accommodate a large shanktype tool holder will have a much slower maximum speed than a machine tool which has been adapted for a shank-type tool holder which is much smaller.

Accordingly, when a cutting tool which may be operated at high speed is used with a machine tool adapted to accommodate large size shanks, it is understood that the cutter cannot be operated at a greater speed than the maximum permitted by the machine tool. Clearly an inefficient situation arises which may be overcome by the incorporation in the machine tool of the concepts of this invention. By permitting the use of a smaller bearing thereby enabling higher rotational speeds of the spindle, it will be seen that the machine tool has greater versatility in using cutters which are designed to operate at high RPM.

To accomplish the changing of a tool or tool holder, of the type disclosed herein, the robotics associated with the machine tool may engage the means provided on the tool or tool holder and grip the same. Thus, to change a cutting tool on a moving spindle or support, the machine tool is typically slowed or stopped permitting the robotics to grip and move the tool or tool holder as the draw bar releases. Once the draw bar is released, movement is then permitted of the tool or tool holder to its position in the storage facility. Thereafter, the robotics may position the next cutting tool to be used proximate the end of the spindle wherein the draw bar will engage and securely fix the tool or tool holder relative thereto.It should be noted that as the draw bar draws the tool or tool holder towards the end of the spindle, the teeth of the two portions of the coupling will intermesh and will self center the tool or tool holder thereby bringing the rotational axis of the cutting tool into line with the rotational axis of the spindle. Thus, it can be seen that a single tool caddy with robotics can control movement of cutting tools to and from the tool caddy and can supply a multiplicity of machine tools because of the interchangeability facilitated by the unique universal coupling of this invention.

In use, a machine tool having a spindle or support with a coupling of this invention associated therewith can engage and support, and in the case of the spindle, drivingly engage, a tool holder or cutting tool having a complimentary portion of the coupling thereon. To accomplish the engagement of the tool or tool holder, the coupling portions are juxtaposed with the teeth intermeshed and a draw bar, or other means, is engaged in such a manner as to positively intermesh the teeth of the coupling portions. The principal advantage of the instant invention is accomplished when the coupling portions are secured together. Coupling very precisely locates the rotational axis of the tool relative to the rotational axis of the spindle or support and due to the increased surface area found in the curvature of the teeth there is a better load distribution and a high torque load capacity.It should be understood that the coupling portions can be used as a self clutching coupling by utilizing a spring or the like having a predetermined biasing force such that the coupling portions will disengage under a predetermined torque loading. The inherent ease of the uncoupling of a tool or tool holder from a spindle or support should be readily apparent in that when the means for holding the two coupling portions together is realised the coupling will essentially fall apart.

While a particular tooth configuration has been disclosed, and it should be noted that the tooth configuration was disclosed in U.S. Patent 4,307,797 and the corresponding U.K. patent 2.059,014 obtained by Illinois Tool Works Inc., and for purposes of this disclosure the teeth are referred to as generally radially extending and generally radially disposed, other forms such as directly radially extending teeth as well as radially disposed means providng a positive engagement and self-centering are intended to be contemplated herein.

Claims (41)

1. A combination comprising a machine tool, a tool or tool holder for use with said machine tool and coupling means for attaching said tool ortool holder to support means on said machine tool, said coupling means having a first portion associated with said tool or tool holder and a second portion associated with said support means, said first and second portions including generally radially disposed means capable of directly intermeshing in a disengageable manner for self-centering of said tool or tool holder relatively to said support means.

2. A combination as set forth in claim 1 wherein there is a tool and said first portion is integral with said tool.

3. A combination as set forth in claim 1 wherein there is a tool holder and said first portion is integral with said tool holder.

4. A combination as set forth in claim 3 wherein said tool holder includes means to permit adjust ment of a tool supported thereby to adjust the distance of the outermost portion of the tool from the support means whereby precise adjustment may be accomplished by resting the tool holder with its integral first portion against a flat surface and measuring therefrom to the outermost portion of the tool.

5. A combination as set forth in any preceding claim wherein said second portion is integral with said support means.

6. A combination as set forth in claim 1 wherein said coupling means forms part of an adapter assembly including means for attaching said first portion of said coupling means to said tool or tool holder and means for attaching said second portion of said coupling means to said support means.

7. A combination as set forth in any preceding claim wherein said generally radially disposed means includes a plurality of generally radially extending teeth.

8. A combination as set forth in claim 7 wherein said generally radially extending teeth are curved teeth, each of the teeth having an inner concave and an outer convex tooth face with each tooth on the first or second portion being so configured that any contact point along both its inner concave and outer convex faces has a spiral angle and a pressure angle which are equal to those of its corresponding contact point along the respective outer convex and inner concave faces of the other portion.

9. A combination as set forth in claim 8 wherein the width of each curved tooth varies from its innermost portion to its outermost portion.

10. A combination as set forth in claim 8 or claim 9 wherein a root is formed between each adjacent pair of the teeth on the first and second portions for receiving debris.

11. A combination as set forth in any preceding claim wherein said support means is a power driven spindle.

12. A combination as set forth in claim 11 wherein securing means are provided for drawing said first portion axially into engagement with said second portion associated with said spindle thereby substantially simultaneously self-centering said tool or tool holder relatively to said spindle and establishing a rigid drive for said tool or tool holder through said coupling means.

13. A combination as set forth in claim 12 wherein said securing means is in the form of a draw bar having a threaded end for engagement in a threaded bore formed in said tool ortool holder.

14. A combination as set forth in claim 12 or claim 13 wherein said spindle is supported by a bearing, said bearing having an inner diameter sufficient to permit passage of said securing means.

15. A combination as set forth in any of claims 11 to 14 wherein said coupling means lies substantially perpendicularly to the axis of rotation of said spindle.

16. A combination as set forth in any preceding claim wherein the maximum extent of said generally radially disposed means associated with said first portion is equal to or less than the maximum extent of said generally radially disposed means associated with said second portion.

17. A combination as set forth in any preceding claim wherein means associated with the tool or tool holder are provided for permitting engagement by handling means for moving the tool or tool holder proximate to and away from the support means.

18. A combination substantially as hereinbefore described with reference to Figures 2 to 4 and 6 or Figure 5 of the accompanying drawings.

19. A tool, for use with support means, comprising a tool body having first means for performing work on a workpiece, second means spaced in an axial direction relatively to said first means for engagement by securing means associated with said support means for drawing said tool in said axial direction towards said support means, and third means concentrically disposed relatively to said second means for engagement by concentrically disposed complementary means associated with said support means, said third means including generally radially disposed means enabling selfcentering coupling of said tool to said complementary means, whereby an axial drawing force sustained by said second means causes said third means to engage and self-center said tool relatively to said complementary means on said support means.

20. A tool as set forth in claim 19 wherein attaching means are provided which fixedly secure said third means to said tool body.

21. A tool as set forth in claim 19 or claim 20 wherein said third means is disposed proximate a plant substantially perpendicular to said axial direction.

22. A tool as set forth in any of claims 19 to 21 wherein said second means includes a threaded bore extending coaxially with said axial direction.

23. A tool as set forth in any of claims 19 to 22 wherein said third means and said complementary means each includes a plurality of curved teeth.

24. A tool as set forth in claim 23 wherein each of said teeth of each plurality has an inner concave and an outer convex tooth face which are so configured that any contact point along both its inner concave and outer convex faces has a spiral angle and a pressure angle which are equal to those of its corresponding contact point along the respective outer convex and inner concave faces of the other of said third means and said complementary means.

25. A tool as set forth in any of claims 19 to 24 wherein fourth means are provided for permitting engagement by handling means for moving the tool proximate to and away from the support means.

26. A tool holder, for use with support means, comprising a tool holder body having first means for receiving a portion of a tool therein, second means for releasably securing said portion of said tool within said first means, third means spaced in an axial direction relatively to said tool holder body for engagement by securing means associated with said support means for drawing said tool holder in said axial direction towards said support means, and fourth means concentrically disposed relatively to said third means for engagement by concentrically disposed complementary means associated with said support means, said fourth means including generally radially disposed means enabling selfcentering coupling of said tool holder to said complementary means, whereby an axial drawing force sustained by said third means causes said forth means to engage and self-center said tool holder relatively to said complementary means on said support means.

27. A tool holder as set forth in claim 26 wherein said second means permits adjustment of a tool supported by said tool holder whereby precise adjustment of the axial extension of the tool from the tool holder may be accomplished by resting said fourth means on a planar surface and measuring from said surface to the outermost point of said tool.

28. A tool holder as set forth in claim 26 or claim 27 wherein attaching means are provided which fixedly secure said fourth means to said tool holder.

29. A tool holder as set forth in any of claims 26 to 28 wherein said first means includes a bore extending coaxially with said axial direction for receiving said portion of the tool.

30. A tool holder as set forth in claim 29 wherein said second means includes at least one screw means extending towards and intersecting the periphery of said bore.

31. A tool holder as set forth in any of claims 26 to 30 wherein said third means includes a threaded bore extending coaxially with said axial direction.

32. A tool holder as set forth in any of claims 26 to 31 wherein said fourth means is disposed proxi mate a plane substantially perpendicular to said axial direction.

33. A tool holder as set forth in any of claims 26 to 32 wherein said fourth means and said complementary means each includes a plurality of curved teeth.

34. A tool holder as set forth in claim 33 wherein each of said teeth of each plurality has an inner concave and an outer convex tooth face which are so configured that any contact point along both its inner concave and outer convex faces has a spiral angle and a pressure angle which are equal to those of its corresponding contact point along the respective outer convex and inner concave faces of the other of said fourth means and said complementary means.

35. A tool holder as set forth in any of claims 26 to 34 wherein fifth means are provided for permitting engagement by handling means for moving the tool holder proximate to and away from the support means.

36. A method of adapting a machine tool to engage and drive a tool or tool holder comprising the step of adapting a spindle, ram or turret of the machine tool to include a coupling portion capable of intermeshing in a disengageable and selfcentering manner directly with a cooperative coupling portion on a tool or tool holder.

37. A method as set forth in claim 36 wherein the step of adapting is accomplished by machining the face of the spindle, ram or turret to have a toothed coupling portion formed thereon.

38. A method as set forth in claim 36 wherein the step of adapting is accomplished by securing a separate annular coupling portion in a concentric manner to the face of the spindle, ram or turret.

39. A method as set forth in claim 38 wherein the step of securing is accomplished by bolting of said coupling portion to said spindle, ram or turret.

40. A method as set forth in any of claims 36 to 39 wherein each of said coupling portions includes a plurality of curved teeth which have generally equal spiral and pressure angles for inner concave and outer convex faces of each tooth.

41. A method of changing tools or tool holders used with a machine tool comprising the steps of engaging a tool or tool holder to be replaced by a movable means, releasing said tool or tool holder from the machine tool, moving the tool or tool holder to be replaced from its in use position, bringing a replacement tool or tool holder to its in use position, positioning said replacement tool or tool holder to permit engagement of a means for drawing said tool or tool holder towards said machine tool, engaging said means for drawing said tool or tool holder towards said machine tool, drawing said tool or tool holder towards said machine tool to establish a rigid drive for said tool or tool holder having substantially zero backlash via cooperable radially extending teeth, which are also responsive to said means for drawing said tool or tool holder towards said machine tool to centre said tool or tool holder.