WO2018086801A1

WO2018086801A1 - A disc milling cutter and a kit comprising such a disc milling cutter

Info

Publication number: WO2018086801A1
Application number: PCT/EP2017/075167
Authority: WO
Inventors: Ralf Lehto
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2016-11-09
Filing date: 2017-10-04
Publication date: 2018-05-17
Anticipated expiration: 2019-05-09
Also published as: EP3321018A1; CN109789498A; EP3321018B1; JP2019536643A; KR102362020B1; JP7157053B2; KR20190084029A; US20200055128A1; CN109789498B

Abstract

A milling tool for metal cutting machining has a tool holder (2) with a shaft (3). At least one disc milling cutter (6) having a central through-hole (12) is mounted on the shaft (3). The disc milling cutter has internal coolant channels extending radially withi n the disc milling cutter and connected to a coolant source through axial through-holes (18) alig ned with axial through-holes (24) of one or more spacer rings (5) also mounted on the shaft (3) so as to provide for feeding of coolant to the disc milling cutter (6) when placed in different positions along the extension of the shaft (3).

Description

A disc milling cutter and a kit comprising such a disc milling cutter

TECHN ICAL FI ELD OF TH E I NVENTION

The present invention relates to a disc milli ng cutter according to the preamble of appended claim 1 and a kit comprising such a disc milling cutter.

The invention relates to disc milling cutters of different designs, such as disc milling cutters designed purely for slot milling or disc milli ng cutters also desig ned for side and face milling . The invention is however particularly useful in so called gang milling having a plurality of disc milling cutters mou nted to the same shaft.

When milling a metal work piece by means of a rotating disc milling cutter, it is often advantageous or even necessary to flush the work piece and/or the disc milling cutter with a coolant/flushing fluid in the form of a gas or a liquid or a mixture of gas and liquid. Hence, such cooling/flushing can be performed for different reasons, e.g . for cooling and/or lubricati ng purpose or for flushi ng away/evacuating chips from the work piece during machini ng . Accordi ngly, the present invention is directed to the problems of cooling the disc milling cutter and flushi ng away the chips from the work piece du ring machining with the disc milling cutter. BACKG ROUN D ART

A known way to achieve a cooli ng/flushing of a disc milling cutter is to simply direct a stream of liquid and/or gas from the outside towards the disc milling cutter and the work piece at a dis- tance from where the actual machining takes place. However, such external cooling/flushing is inefficient. I n particular, flush- ing with a coolant/flushing fluid for purpose of flushing away/chips by means of one or more external coolant/flushing fluid jets directed towards the disc milling cutter and the work piece from the outside will be very ineffective as most of the coolant/flushing fluid will not reach the machi ning area (inside a machined slot/groove) where it could be used for flushi ng away/evacuating the chips. I n case of a liquid coolant this inefficient cooling/flushing will also result in a formation of a large amount of waste liquid , which has to be collected and filtered or disposed of .

EP 2 929 967 A1 discloses a disc milling cutter to be used for milling relatively deep and narrow slots. This known disc milling cutter is provided with i nternal coolant/flushing fluid channels extending radially within the disc milling cutter from a radially inner (inlet) openi ng located i n an inner central portion of the disc milling cutter to an outlet openi ng in the outer peripheral portion of the disc milling cutter. The internal coolant/flushing fluid channels are supplied with coolant/flushing fluid through a tool holder shaft opening on an end surface on which the disc milling cutter is bearing . Although this known disc milling cutter provides efficient cooling/flushing , while avoiding the above disadvantages of external cooling/flushing , it exhibits some restrictions. One such restriction is that the use thereof requires a tool holder specifically designed for this disc milli ng cutter. Accordingly, a standard tool holder shaft having a central coolant/flushing fluid outlet openi ng may not be used for such a disc milling cutter. Fu rthermore, such a known disc milling cutter can only be used for metal cutting machining while rotating in one predetermined direction . Another restriction is that more than one such disc milling cutter may not be connected to the same tool holder for enabling so called gang milling . SU MMARY OF TH E I NVENTION

The object of the present invention is to provide a disc milling cutter according to the preamble of appended claim l and a kit comprising such a disc milling cutter being improved in view of the restrictions mentioned above.

This object is with respect to the disc milling cutter according to the invention obtained by providing the disc milling cutter with the characterizing feature of claim 1 .

By the at least one axially directed inlet opening in the disc milling cutter being formed by an axial through-hole extending throug h the disc milling cutter from a first axially directed side abutment surface to a second axially directed side abutment su rface on the opposite side of the inner central portion of a disc milling cutter, the disc milling cutter can both receive and further communicate coolant/flushing fluid axially on the outside of a standard tool holder shaft having a central coolant/flushing fluid channel with a central outlet at an end of the shaft (which is communicating coolant/flushing fluid via a locking means mounted to the end of the standard shaft and fu rther described below i n connection with the kit) . The disc milling cutter allows the mounti ng of not just one but several disc milli ng cutters (gang milling) in any desired axial position/configu ration along the standard tool holder shaft (by mounting spacer ring(s) further described below in connection with the kit) . The disc milling cutter may also be used for carrying out metal cutting milling of a work piece by rotation of the shaft of the tool holder in one di- rection and then the rotation direction for such milling may be changed by simply removi ng the disc milli ng cutter from the shaft and mou nting it oppositely turned to the shaft. Thus, the flexibility of the use of such a disc milling cutter is increased with respect to the known disc milling cutter of the type de- scribed in the introduction. The "coolant channel" in accordance with the invention should hereby be interpreted to serve the pu r- pose of cooling the cutting edges/inserts of the disc milling cutter and/or flushing away/evacuating the chips from the work- piece during milli ng . According to an embodiment of the invention the disc milling cutter has at least one internal coolant distribution channel extending at least partially around the central through-hole and connecting the at least one axially directed i nlet opening with at least two radially extending coolant channels. An advantageous flow distribution can thereby be achieved between several radially extending coolant channels having their inlet openings connected to the same coolant distribution channel .

According to another embodiment of the invention the disc mill- ing cutter has a plurality of axial through-holes forming the axially directed inlet openings, which is favourable for obtaining an efficient cooling/flushing at different peripheral portions around the circumference of the disc milling cutter, wherein the cooling/flushing efficiency may i n particular be further increased when the axial through-holes forming the axially directed inlet openings are evenly distributed around the central throug h-hole as in another embodiment of the invention .

According to another embodiment of the invention all axial through-holes forming the axially directed inlet openings open into said at least one internal coolant distribution channel . I n this way the coolant can be distributed from one i nlet to several radially extending coolant channels. According to another embodi ment of the invention the internal coolant distribution channel is an annular channel su rrounding the central through-hole and connecting all axially directed inlet openings with radially extending coolant channels of the disc milling cutter. This constitutes a simple and efficient design for obtaining a u niform cooling/flushing of the disc milling cutter, while avoiding a risk of failing to provide any radially extending coolant channel with coolant/flushing fluid as a consequence of coolant/flushing fluid faili ng to reach any of the axial through- holes of the disc milling cutter. According to another embodiment of the invention the at least one outlet opening of the at least one internal coolant channel is located in a chip pocket formed in the peripheral portion of the disc milling cutter. Chips formed by metal cutti ng machi ning of the disc milling cutter are in this way efficiently re- moved/evacuated from the chip pocket and the workpiece (in particular when milling slots/grooves i n the workpiece) .

The object of the present invention is also obtained by providing a kit according to the claim directed to the kit.

By combining at least one disc milling cutter according to the present invention with at least one spacer ring with a central throug h-hole for mounti ng the spacer ring onto the same shaft of the rotatable tool holder as the disc milling cutter, in which the spacer ring has means configured to provide a rotary preventing attachment of the spacer ring in a predetermined angular position i n relation to the shaft of the tool holder and the spacer ri ng comprises at least one axial through-hole located to communicate with the at least one axially directed inlet opening in the disc milli ng cutter when the spacer ring is abutti ng the first or second axially directed side abutment surface of the disc milli ng cutter i n the predetermined angular position , it will be possible to conduct coolant/flushi ng fluid through the spacer ring to the disc milling cutter and by that use the at least one spacer ring to mount the disc milling cutter at different axial locations along the extension of the tool holder shaft and still obtain the efficient and flexible internal cooling/flushing described above. It also allows for several disc milling cutters with one or several spacer rings to be mounted on the shaft in a desired gang milling con- figuration. Accordi ng to an embodiment of the kit this comprises a plurality of disc milling cutters, and at least one disc milling cutter has said means configured to provide a rotary preventi ng attachment of the disc milling cutter to obtain this i n an angular position with respect to the shaft differi ng from such an angular position of another disc milling cutter in the sense that the cutti ng edges of at least one disc milling cutter or of the cutting inserts thereof are circumferentially displaced with respect to the cutting edges of another disc milling cutter or of the cutting inserts thereof when attached to the shaft. This feature offers an option to arrange a disc milling cutter of the kit with respect to another disc milling cutter with the cutting edges ci rcumferentially displaced and still provide efficient cooling/flushing of the disc milling cutter through alig nment of the axial through-holes thereof with the axial through-holes of a spacer ring . This enables an arrangement of a plurality of disc milling cutters on the same tool holder shaft for gang milling so that the cutting edges associated with some disc milling cutters will not hit the work piece at the same time as cutting edges associated with other disc milling cutters to reduce/elimi nate the tendency for vibrations to arise as well as to keep the noise down, while obtaining efficient cooling/flushing in all the disc milling cutters.

This same result may also be obtained by providing a kit for which the number of axial through-holes in at least one disc milling cutter is a multiple of the number of the axial through-holes of the spacer ring so that at most half of the axial through-holes of the disc milling cutter are located to communicate with an axial through-hole of a spacer ring in the predetermined angular position . This means that a disc milling cutter may be tu rned with respect to an adjacent spacer ring for obtaining alig nment with the axial throug h-holes of the spacer ring with other axial throug h-holes of the disc milli ng cutter than before. A condition for enabli ng such turning is of course that the means for rotary preventing attachment of the disc milling cutters are correspond- ingly adapted with respect to the ci rcumferential position thereof on the disc milling cutter.

Accordi ng to another embodiment of the kit the axial throug h- holes in the spacer ri ng are evenly distributed around the central through-hole.

According to another embodiment of the invention the kit fu rther comprises locki ng means for securi ng the at least one disc mill- ing cutter and the at least one spacer ring on the shaft of the rotatable tool holder, the locking means comprising a lid bei ng mountable to an end of the shaft by an attachment member clamping the lid onto the spacer ring or the first or second axial- ly directed side abutment su rface of the disc milling cutter in the secu ring state of the locking means, wherein the lid comprises a coolant connection for commu nicating coolant between a central coolant channel mouthing at the end of the shaft and the axial through-hole(s) in the spacer ring or the disc milling cutter in contact with the lid. The provision of the kit with such a locking means enables the use of a standard tool holder for the use of the at least one disc milling cutter of the kit for metal cutting machining while obtaining efficient cooling/flushing thereof. The position of the disc milling cutter along the tool holder shaft may also be modified by choosing to have a disc milling cutter ar- ranged next to said lid or one or more spacer rings separating the disc milli ng cutter from said lid .

According to an embodiment of the kit the attachment member is a clamping screw having an external threaded shank for thread- ing into an internal thread of the central coolant channel in the end of the shaft, the shank of the clampi ng screw comprisi ng at least one feed channel of the locking means for coolant communication between the central coolant channel of the shaft and the coolant connection of the lid . Thus, such a milling tool may use a standard tool holder for obtai ning efficient cooling of the at least one disc milling cutter of the milling tool making such a milling tool very attractive from the cost point of view.

According to another embodi ment of the kit it further comprises the tool holder having the central coolant channel configured to be connected to a source of coolant at a rear end of the tool holder.

According to another embodiment of the kit the tool holder has a collar with an axially directed mounting surface for abutting the spacer ring or the axially directed side surface of the disc milling cutter mounted on the shaft, wherein the tool holder is provided with at least one further coolant channel connected to the central coolant channel and ending in a feed opening in the mount- ing surface of the collar, which feed openi ng is positioned to provide coolant to the at least one axially directed inlet opening in the axially di rected side abutment surface of the disc milling cutter or the axial through-hole of the spacer ring . Besides the possibility to arrange one or more disc milling cutters according to the invention in different positions along the tool holder shaft this embodiment of the invention results in a possibility to increase the coolant flow in the internal coolant channels of the disc milli ng cutter by feeding coolant to the axial through-holes thereof from both sides of the disc milling cutter.

Other advantageous features as well as advantages of the present invention appear from the description followi ng below.

BRI EF DESCRI PTION OF TH E DRAWI NGS

With reference to the appended drawings, below follows a specific description of embodiments of the invention cited as examples. I n the drawings:

Fig . 1 is an exploded perspective view of a kit accordi ng to first embodiment of the invention,

Fig . 2 is a schematic cross section view of the kit shown

Fig . 1 in an operative state, Fig . 3 is an exploded and partially sectioned perspective view of the disc milling cutter shown in Fig . 1 and a spacer ring arranged next thereto,

Fig . 4 is a view similar to Fig . 2 of a kit according to a se- cond embodiment of the invention in an operative state, is a view of a disc milling cutter of a kit of an embodiment of the invention, and is a view similar to Fig . 2 of a kit according to a thi rd embodiment of the invention in an operative state.

DETAI LE D DESCRI PTION OF EMBOD I M ENTS OF TH E I NVENTION

A milling tool 1 according to a first embodiment of the invention suitable for slot milling as well as face milli ng and shoulder mi 11- ing and also for so called gang milling , which will be explained further below when making reference to Fig . 4, will now be described while making reference simultaneously to Figs. 1 -3. The milling tool has a rotatable tool holder 2 to be rotary preventing attached to a milling machine and having a shaft 3 with a mem- ber 4 for rotary preventi ng attachment of at least one spacer ring 5 and at least one disc milling cutter 6 according to the pre- sent invention by corresponding cut outs 7, 8 therein. The thickness of a disc milling cutter may be any but may typically vary from 2 mm to 26 mm and mostly from 6 mm to 26 mm resulting in correspondi ng slot widths when used for slot milling . The di- ameter of the disc milling cutter is for example 60 mm-320 mm .

The desig n of a disc milling cutter 6 according to a first embodiment of the invention mainly appears from Fig . 3, and the disc milling cutter has an outer peripheral portion 9 provided with a nu mber of seats 1 0 for cutting inserts 1 1 . The disc milling cutter has a central through-hole 1 2 for mounti ng the disc milling cutter onto the shaft 3 of the tool holder 2. The disc milling cutter has further internal coolant channels 1 3 extending radially within the disc milling cutter from a radially inner opening 1 4 located in an inner central portion 1 5 of the disc milling cutter to an outlet opening 1 6 in the outer peripheral portion 9 located in a chip pocket 1 7 of the disc milling cutter. The number of such internal coolant channels are in this embodiment the same as the nu mber of seats for cutting inserts.

The i nner central portion 1 5 of the disc milli ng cutter is provided with fou r axial through-holes 1 8 extending throug h the disc milling cutter from a first axially directed side abutment surface 1 9 to a second axially di rected side abutment surface 20 (hidden i n Fig . 1 ) on the opposite side of the inner central portion of the disc milling cutter. These axial throug h-holes are forming axially directed inlet openings 21 commu nicating throug h an annular internal coolant distribution channel 22 with the inlet openings 1 4 of the internal coolant channels 1 3.

The spacer rings 5 have also a central through-hole 23 for mounting the respective spacer ring onto the same tool holder shaft 3 as the disc milling cutter 6. Each spacer ring 5 fu rther comprises four axial throug h-holes 24 located to communicate with an axially directed i nlet opening 21 each in the disc milling cutter or an axial through-hole 24 in another spacer ring each when the spacer ring is abutti ng the fi rst or second axially directed side abutment su rface 1 9, 20 of a disc milling cutter or another spacer ring when the spacer ri ng(-s) and disc milling cutter(-s) are rotary preventing attached in a predetermined an- gular position in relation to a shaft 3 of the tool holder 2.

The tool holder 2 has a central coolant channel 25 configured to be connected to a source of coolant and extending in the shaft 3 to an opening 26 i n an end surface 27 of the shaft. The tool fur- ther comprises a locking means 28 for secu ring one or more disc milling cutters and spacer rings on the shaft 3. This locking means comprises a lid 29 mou ntable to an end of the shaft by an attachment member 30 in the form of a clamping screw having an external shank for threading into an internal thread of the central coolant channel 25 in the end of the shaft so as to be tig htened for clamping the lid 29 onto a spacer ring as shown i n Fig . 2 or onto the first or second axially directed side abutment su rface of a disc milling cutter in a securing state of the locking means. The shank of the clamping screw 30 comprises at least one feed opening 33 of the locki ng means for coolant communication between the central coolant channel 25 and a coolant connection 31 formed by the lid 29 to the axial through-holes 24, 1 8 in a spacer ri ng or disc milling cutter in contact with the lid 29 as appears from Fig . 2.

It is shown through arrows A in Fig . 2 how coolant will reach the internal coolant channels 1 3 of the disc milling cutter 6 throug h a central coolant channel 25 of the tool holder 2, the feed opening 33 of the screw shank the coolant connection 31 of the lid , the axial throug h-holes 24 of the spacer rings 5 and the axial throug h-holes 1 8 of a disc milling cutter and the i nternal coolant distribution channel 22 thereof . This means that the disc milli ng cutter 6 may be arranged in different positions along the shaft 3 and still efficient feeding of coolant to the disc milli ng cutter will be ensured by the use of a standard tool holder as shown in Fig . 1 and 2. The spacer rings 5a arranged closer to the collar 32 of the tool holder with an enlarged cross section with respect to the shaft 3 have not to be spacer rings according to the invention provided with axial throug h-holes, although it may be suitable to have spacer rings of only one type i n the kit used i n the milling tool according to the invention.

Fig . 4 illustrates the flexibility of the milling tool according to this embodiment of the i nvention and how several disc milli ng cutters 6 may be mounted on the tool holder shaft 3 for carrying out gang milling , and it is obvious that the number of the disc milling cutters and the mutual positions thereof may be altered by different arrangements of spacer rings, and it is of course also possible to have spacer ri ngs of the type shown in Fig . 1 with different thicknesses for varying positions and mutual distances of the disc milling cutters.

Fig . 5 indicates the possibility to provide one or several disc milling cutters 6 with a nu mber of axial throug h-holes 1 8 being a multiple of the number of the axial throug h-holes 24 of the spac- er rings 5, which in this case means that half of the eight throug h-holes of the disc milling cutter are located to communicate with an axial through-hole of a spacer ring in said predetermined angular position. This means that the disc milling cutter shown in Fig . 5 may be rotated by 45° with respect to a spacer ri ng according to Fig . 3 between two positions of alignment of the axial through-holes in the disc milli ng cutter with axial through-holes on the spacer ring , so that i n case of a plurality of disc milling cutters mounted on the tool holder shaft these may be arranged to have the cutting inserts thereof attacking a work piece at instants separated in time provided that the disc milling cutters have the cut outs 8 correspondingly positioned and still all disc milling cutters will be efficiently provided with coolant. The same result may be obtai ned by having just as many axial through-holes 1 8 in all disc milling cutters 6 as in the spacer rings and having the axial through-holes 1 8 in some disc milling cutters in another relative circumferential position to the cutting edges than the other disc milling cutters.

Fig . 6 illustrates a kit according to a third embodiment of the i n- vention in an operative state differing from the kit shown in Fig . 2 by the design of the tool holder 1 02. The tool holder is provided with additional coolant channels 1 40, 1 41 emerging from the central coolant channel 1 25 and ending in a respective feed opening 1 42, 1 43 in the mou nting su rface of the collar 1 32. Each feed opening is positioned to provide feeding of coolant from the coolant channel thereof to one axially di rected inlet opening in an axially directed side abutment su rface of the disc milling cutter 1 06 through an axial through-hole of the spacer rings 1 05 mounted on the tool holder shaft 1 03 between the col- lar 1 32 and the disc milling cutter 1 06. The number of such additional channels 1 40, 1 41 inside the tool holder is preferably, but not necessarily, at least as high as the number of the axial through-holes in the disc milling cutter. I n the embodiment shown in Fig . 6 it is possible to provide for feeding of coolant to the disc milli ng cutter only through the channels mouthing i n the collar 1 32 or to have the central coolant channel 1 25 be open to the lid 1 29 for feeding coolant additionally along the same flow part as shown i n Fig . 2 as indicated by the arrows A. I n the latter case the pressure of the coolant reaching the internal cool- ant channels 1 3 of the disc milling cutter will be increased by supplying coolant thereto through the axial through-holes from both axially directed side abutment surfaces of the disc milli ng cutter.

The invention is of course not restricted to the embodiments thereof described above, but many possibilities to modifications thereof would be apparent to a person with skill i n the art without departing from the scope of the invention as defined in the appended claims. "Radially" with respect to the extension of the internal coolant channels inside the disc milling cutter is to be interpreted as an extension from a central portion of the disc milling cutter towards a peripheral portion thereof and this extension has not necessarily to be exactly radial , i .e. i ntersecti ng a center axis of the disc milli ng cutter. The same reasoning applies to the use of "axial" for for instance the axial through-holes in the disc milling cutters and the spacer rings, which is to be interpreted as these have an extension with a main component in the axial direction.

It is obvious that the axial through-holes of the disc milling cutter may open directly into an internal coolant channel thereof without any internal distribution channel , or the annular internal distribution channel may be replaced by a plurality of i nternal distribution channels each extending partially around the central throug h-hole of the disc milling cutter and connecting at least one axially directed inlet opening of an axial through-hole with at least two radially extending coolant channels. The disc milli ng cutter may be provided with cutting edges on the very disc. The i nternal coolant channels of the disc milling cutter may have an outlet in the peripheral portion of the disc on an axially directed side abutment surface. The spacer rings have of course not to have a circular outer contour line.

This is to mention only some of said possible modifications within the scope of the invention.

Claims

A disc milling cutter for metal cutting machining comprising:

• an outer peripheral portion (9) provided with a number of cutting edges or a number of seats (10) for cutting inserts (11 ),

• a central through-hole (12) for mounting the disc milling cutter (6) onto a shaft (3, 103) of a rotatable tool holder (2, 102),

• means (8) configured to provide a rotary preventing attachment of the disc milling cutter (6) in a specific angular position in relation to the shaft penetrating the central through-hole (12),

• at least one internal coolant channel (13) extending radially within the disc milling cutter (6) from a radially inner opening (14) located in an inner central portion (15) of the disc milling cutter to at least one outlet opening (16) in the outer peripheral portion (9), and

• at least one axially directed inlet opening (21) in a first axially directed side abutment surface (19) of the inner central portion (15) of the disc milling cutter for receiving the coolant and communicating with the radially inner opening (14) of the internal radially extending coolant channel (13),

characterized in that the at least one axially directed inlet opening (21) is formed by an axial through-hole (18) extending through the disc milling cutter (6) from the first axially directed side abutment surface (19) to a second axially directed side abutment surface (20) on the opposite side of the inner central portion (15) of the disc milling cutter.

A disc milling cutter according to claim 1, characterized in that it has at least one internal coolant distribution channel (22) extending at least partially around the central through- hole (12) and connecting the at least one axially directed in- let opening (21 ) with at least two radially extending coolant channels (1 3) .

A disc milling cutter according to claim 1 or 2, characterized in that it has a plu rality of axial through-holes (1 8) forming the axially directed inlet openings (21 ) .

A disc milling cutter according to claim 3, characterized in that the axial through-holes ( 1 8) forming the axially directed inlet openings (21 ) are evenly distributed around the central throug h-hole (1 2) .

A disc milling cutter according to claims 2 and 3, characterized i n that all axial through-holes (1 8) forming axially directed inlet openings (21 ) open into said at least one internal coolant distribution channel (22) .

A disc milling cutter according to claim 2, characterized in that the internal coolant distribution channel (22) is an annular channel surrounding the central throug h-hole (1 2) and connecting all axially di rected inlet openings (21 ) with the radially extending coolant channels (1 3) of the disc milling cutter.

A disc milling cutter according to any of the preceding claims, characterized in that the at least one outlet opening (1 6) of the at least one internal coolant channel (1 3) is located in a chip pocket (1 7) formed in the peripheral portion (9) of the disc milling cutter.

A kit comprising

a) at least one disc milling cutter (6) for metal cutting according to any of the preceding claims and

b) at least one spacer ring (5) with a central throug h-hole (23) for mounting the spacer ri ng onto the same shaft (3, 1 03) of the rotatable tool holder (2, 1 02) as the disc milling cutter, the spacer ring having means (7) configured to provide a rotary preventing attachment of the spacer ring in a predetermi ned angular position in relation to the shaft (3, 1 03) of the tool holder, wherein the spacer ring comprises at least one axial through-hole (24) located to commu nicate with the at least one axially directed inlet opening (21 ) i n the disc milling cutter (6) when the spacer ring (5) is abutting the first (1 9) or second (20) axially directed side abutment surface of the disc milling cutter in the predetermined angular position.

A kit according to claim 8, characterized in that it comprises a plurality of disc milling cutters (6) , and that at least one disc milling cutter (6) has said means (8) configu red to provide a rotary preventi ng attachment of the disc milling cutter (6) to obtai n this in an angular position with respect to the shaft (3) differing from such an angular position of another disc milling cutter i n the sense that the cutting edges of at least one disc milling cutter or of the cutting inserts thereof are circu mferentially displaced with respect to the cutting edges of another disc milling cutter or of the cutting inserts thereof when attached to the shaft.

A kit according to claim 8 or 9, characterized in that the number of axial through-holes (1 8) in at least one disc milling cutter (6) is a multiple of the nu mber of the axial throug h-holes (24) of the spacer ring (5) so that at most half of the axial through-holes of the disc milling cutter are located to communicate with an axial through-hole (24) of a spacer ring (5) in the predetermined angular position .

A kit accordi ng to claim 1 0, having at least one disc milling cutter according to claim 4, characterized in that the axial throug h-holes (24) in the spacer ring (5) are evenly distributed around the central throug h-hole (23) .

12. A kit according to any of claims 8-11, characterized in that it comprises a plurality of spacer rings (5) and/or a plurality of disc milling cutters (6).

13. A kit according to any of claims 8-12, characterized in that it further comprises locking means (28) for securing the at least one disc milling cutter (6) and the at least one spacer (5) ring on the shaft (3, 103) of the rotatable tool holder (2, 102), the locking means comprising a lid (29, 129) being mountable to an end of the shaft by an attachment member (30) clamping the lid onto the spacer ring or the first or second axially directed side abutment surface of the disc milling cutter in the securing state of the locking means, wherein the lid (29, 129) comprises a coolant connection (31) for communicating coolant between a central coolant channel (25, 125, 225) mouthing at the end of the shaft and the axial through-hole(s) (24, 18) in the spacer ring (5) or the disc milling cutter (6) in contact with the lid.

14. A kit according to claim 13, characterized in that the attachment member (30) is a clamping screw having an external threaded shank for threading into an internal thread of the central coolant channel in the end of the shaft, the shank of the clamping screw comprising at least one feed channel (33) of the locking means for coolant communication between the central coolant channel (25, 125, 225, 140, 141, 240, 241) of the shaft and the coolant connection of the lid.

15. A kit according to claims 13 or 14, characterized in that it further comprises the tool holder (2, 102) having the central coolant channel (25, 125) configured to be connected to a source of coolant at a rear end of the tool holder.

16. A kit according to claim 15, characterized in that the tool holder (102) has a collar (132) with an axially directed mounting surface for abutting the spacer ring (5) or the axially directed side abutment surface of the disc milling cutter mounted on the shaft, wherein the tool holder is provided with at least one further coolant channel (140, 141) connected to the central coolant channel and ending in a feed opening (142, 143) in the mounting surface of the collar (132), which feed opening is positioned to provide coolant to the at least one axially directed inlet opening (21) in the axially directed side abutment surface (19, 20) of the disc milling cutter (6) or the axial through-hole (24) of the spacer ring (5).