TECHNICAL FIELD

The present invention relates to a hollow punch and a system for removably blocking the punch to a shaft of a machine for processing leather.

BACKGROUND ART Removable blocking systems of a hollow punch to a shaft are known in the prior art, and comprise mechanical blocking of the punch in a seating provided at an end of the drive shaft.

A first known system for blocking a hollow punch to a shaft is illustrated in figure 1 , and comprises: a tool-bearing chuck 3 fixed to a terminal end of the shaft 5; a seating 500 of the shaft destined to house a shank 8 of the punch 2 and defined by flexible longitudinal tabs 3C of the tool-bearing chuck 3; a threaded portion 4 located immediately above the tool-bearing chuck 3; and a blocking collar 1 screwable above the tool-bearing chuck 3, when the shank 8 of the punch 2 is inserted in the seating 500, for unremovably rigidly coupling the punch 2 to the shaft 5.

The blocking collar 1 internally bears a nut 6 destined to couple to the corresponding threaded portion 4 of the shaft 5, and affords a truncoconically- developing portion 7.

The tool-bearing chuck 3 is obtained starting from a tubular element 3A in which a plurality of longitudinal slits 3B are afforded, such as to identify the flexible longitudinal tabs 3C for receiving the shank 8 of the punch.

The blocking of the punch 2 to the relative shaft 5 is performed by initially positioning the shank 8 of the punch 2 in the seating 500 and thereafter screwing the blocking collar 1 on the threaded portion 4. In this way, the truncoconical portion 7 determines a progressive nearing of the flexible tabs 3c up until they abut against the shank 8 and block it.

The removable blocking obtained in this was prevents any relative movement of rotation and/or translation of the punch 2 with respect to the shaft 5.

A further blocking system of known type of a punch to a shaft is illustrated in figure 2, and comprises: a seating 11 afforded in the terminal part 150 of the shaft 10 for receiving a corresponding shank 12 of a punch 13; and a grubscrew 5 insertable internally of a threaded hole 14 having a radial development and afforded in the terminal part 150 of the shaft 0 and opening internally of the seating 11.

The blocking of the punch to the shaft is performed by positioning the shank 12 of the punch 13 in the seating 11 and thereafter screwing the grubscrew 15 into the threaded hole 14 up until the grubscrew 15 intercepts a corresponding portion of the shank 12; the friction that occurs between the terminal part of the grubscrew 15 and the shank 12 prevents rotation and/or translation between the punch 13 and the shaft 10.

The operations of engagement/disengagement of the punch to and from the shaft in the first and second blocking systems described are performed manually by an operator as they are in themselves complex and require a contemporary intervention on several elements of the blocking system. With reference to the first blocking system, with one hand the operator has to keep the shank 8 of the punch 2 blocked in the seating 500, while with the other had he has to screw or unscrew the collar 1 onto/from the threaded portion 4; as for the second above-described blocking system, with one hand the operator has to keep the shank 12 of the punch 13 blocked in the seating 11 while screwing/unscrewing the grubscrew 15 into/from the threaded hole 14. This inevitably leads to higher labour costs and a limitation in productivity, especially in those applications which require frequent replacements of the punches in order to perform specific operations on the leather. A third known system for blocking a tool to a shaft is described in US patent US 5 094 134 and comprises: a seating afforded in the terminal part of the shaft; a permanent cylindrical magnet inserted in the seating and fixed to the upper wall thereof; a cylindrical spacer element inserted in the seating inferiorly of the magnet and fixed thereto; a pair of bearings, respectively a first thrust bearing fixed inferiorly of the spacer element and a second radial bearing, inserted and fixed in a housing afforded in the lower end of the seating; a portion of the tool shank made of a suitable material for being magnetically attracted and the terminal portion of the shank, substantially conically shaped.

The tool is inserted internally of the seating identified by the internal ring of the second radial bearing up to when the conical portion encounters the first bearing; the tool in this configuration is axialiy retained by means of the magnetic force of attraction exerted by the permanent magnet on the portion of the tool shank made of a suitable material for being magnetically attracted and is free to rotate with respect to the shaft seating in which it is inserted.

The third type of blocking system, though enabling a rapid and simple engagement/disengagement of the tool from the shaft, is not suitable for blocking punch tools having an asymmetrical cutting head because as the punch is free to rotate with respect to the shaft it is not possible, from a knowledge of the relative orientation of the shaft with respect to a predefined angular reference, to calculate with certainty the position taken on by the cutting head of the punch with respect to the angular reference.

Further, this blocking system exhibits drawbacks even with punch-tools having a symmetrical cutting head, as the magnetic force of attraction which is exerted by the permanent magnet on the shank of the punch inserted in the seating is not sufficient to retain the punch should the punch, during a working operation, stick in the leather; in this case during the distancing of the shaft from the leather the punch would disengage from the seating and an operative would have to intervene in order to replace it in the seating.

SUMMARY OF INVENTION In the light of the above, it is ,an aim of the present invention to provide a technical solution which enables overcoming the drawbacks of the above-described known- type solutions, i.e. to make available a hollow punch and a blocking system for blocking a punch to a shaft of a machine for working leather which enables rapidly engaging and disengaging the punch to/from the shaft and acting exclusively and directly on the punch with operations that can also be carried out by an automatic punch-changing device.

The above-cited aim is obtained by means of a punch for working leather as set out in claim 1 , and with a blocking system of a punch to a shaft as in claim 9.

The hollow punch for working leather, insertable in a seating of a shaft of a machine for working leather in which the a blocking element is fixed, in an internal lateral wall, a blocking element such as to project from the seating, comprises: a shank; a portion of end of the shank conformed such as to engage with the projecting portion of the blocking element such as to enable advancing of the shank along the seating; and a recess afforded in a lateral wall of the shank such as to joint-couple with the blocking element, when the portion of end of the shank is engaged with the blocking element, by means of a rotation of the punch in a predetermined rotation direction, with a consequent axial blocking of the punch with respect to the seating.

The punch of the invention is engaged to a shaft by means of insertion of the shank in the seating such that the portion of the end of the shank engages with the blocking element and the subsequent rotation of the punch in the predetermined rotation direction up to removably axially and angularly blocking it in rotation in the predetermined rotating direction; likewise, to disengage the punch from the shaft it is sufficient to rotate the punch with respect to the seating in the opposite direction to the predetermined rotation direction.

This sequence of engagement/disengagement operations involves only the punch; this enables rapidly and easily coupling/decoupling the punch from the shaft.

The blocking system of a punch to a shaft of a machine for working leather comprises a punch as in claim 1 , a seating provided at the terminal end of a shaft for receiving the shank of the punch; a blocking element fixable to an internal lateral wall of the seating in order to project with respect thereto; this blocking element being destined, when fixed in the seating, to engage with the end portion of the shank such as to enable advancement of the shank along the seating and also being destined to joint-couple with the blocking element when the portion of the end of the shank is engaged with the blocking element, by means of a rotation of the punch in a predetermined rotation direction, with a consequent axial blocking of the punch with respect to the seating.

In order to engage the punch to the shaft, the proposed blocking system comprises inserting the punch in the seating such that the portion of the end of the shank engages with blocking elements and thereafter rotates the punch in the predetermined rotation direction up to removably axially and angularly blocking it with respect to a rotation about the predetermined rotation direction; likewise, in order to disengage the punch from the shaft it is sufficient to rotate the punch with respect to the seating in the opposite direction to the predetermined rotation direction and then remove it from the seating.

The sequence of operations illustrated in the preceding paragraph and provided for engaging/disengaging the punch to/from the shaft can easily be performed by an operator by intervening only on the punch; or it can be performed by an automatic device for changing punches. A further embodiment of the blocking system comprises the use of an element destined to generate a magnetic force of attraction, fixed to the upper wall of the seating, and at least a part of the shank made of a material destined to be magnetically attracted; the insertion of the shank of the punch in the seating is facilitated by the magnetic attraction force exerted by the magnet of the shank of the punch, which further enables retaining the punch in the seating even when the punch is not stably blocked to the seating by joint-coupling of the recess with the blocking element.

The possibility of retaining the punch in the seating by magnetic force of attraction advantageously enables, when the shank of the punch has been inserted in the seating and the point of the punch has been contacted on a piece sample leather or a portion of the semifinished piece itself, joint-engaging the recess and the blocking element by simple rotation of the shaft; this advantageously enables engaging/disengaging the punch to/from the shaft by a sequence of operation which can be easily performed by an operator or any automatic punch-changing system.

Also defined is a method for obtaining a punch, comprising stages of: predisposing a punch having a cylindrical shank; removing material from the shank of the punch in order to create an undercut such that a portion of the shank in which the undercut has been created can engage with the projecting portion of the blocking element, such as to enable advancing of the shank along the seating; removing material from the shank of the punch such as to create a recess conformed such as to joint-engage with the projecting portion of the blocking element.

The proposed method advantageously enables realising a punch which engages/disengages to/from the shaft by a sequence of operations that can be easily performed by an operator or any automatic punch-changing system.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention, and advantageous technical-functional characteristics thereof correlated to these embodiments, which are only in part derivable from the above description, will be described in the following of the present description, according to what is set out in the claims and with the aid of the accompanying figures of the drawings, in which: figure 1 illustrates, in an exploded lateral schematic view, a shaft and relative terminal parts thereof, a punch and a first system of known type for blocking the punch to the shaft; figure 2 illustrates, in an exploded lateral schematic view, a shaft and relative terminal parts thereof, a punch and a further system of known type for blocking the punch to the shaft; figure 3 illustrates, in an exploded perspective view, only the terminal part of the shaft in which the housing seating is afforded, the punch of the present invention and the elements of the blocking system of the present invention according to a preferred embodiment; figures 4 to 6 illustrate views of an axial section of the terminal part of the shaft, the punch and the blocking system of the present invention according to the embodiment of figure 3, respectively in a configuration in which the punch is inserted in the seating of the shaft and unstably constrained thereto, in a configuration in which the punch is coupled to the blocking element but not stably constrained to the shaft and a configuration in which the punch is stably blocked to the shaft; figures from 7 to 9 illustrate respective views according to section planes VII-VII, VIII-VIII, IX-IX of figures 4, 5 and 6 of the terminal part of the shaft, the punch and the blocking system of the present invention according to the embodiment of figure 3; figure 10 illustrates a view of an axial section of the terminal part of the shaft of the punch and the blocking system of the present invention according to a further embodiment; figure 11 illustrates an axial section of the terminal part of the shaft, the punch and the blocking system of the present invention according to a still further embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to figures from 3 to 9, the terminal part of a shaft 30 is illustrated, in which a cylindrical housing seating 31 is fashioned, and a punch 21 of the present invention. Specifically, the shaft 30 is an integrated part of an automatic machine for working leather and the like, not shown in the appended figures as it is not part of the invention.

A blocking element 23 is fixed to the seating 31 in an internal lateral wall 38 such as to project with respect to the seating 31 , and is inserted through a through-hole 24 afforded in the external wall of the terminal part of the shaft 30 and opening in the seating 31.

The punch 21 of the present invention comprises: a shank 22; an end portion 44 of the shank 22 conformed such as to engage with the projecting portion of the blocking element 23, when the blocking element 23 is fixed to the seating 31, such as to enable advancing of the shank 22 along the internal lateral walls 38 of the seating 31 ; and a recess 25 afforded in a lateral wall of the shank 22 in order to joint-couple with the blocking element 23 when the end portion 44 of the shank 22 is engaged with the blocking element 23 by means of a rotation of the punch 21 in a predetermined rotating direction W, with a consequent axial blocking of the punch 21 with respect to the seating 31.

A cylindrical permanent magnet 32 is further inserted in the seating 31 , fixed to the upper wall thereof 31 opposite the opening thereof, for example by gluing. The blocking element 23 has a substantially cylindrical shape and can be fixed to the inside of the seating 31 for example by mechanical interference with the through-hole 24 it engages with; this cylindrical element 23 is fixed to the internal lateral wall 38 of the seating 31 below the permanent magnet 32.

The shank 22 of the punch 21 has a substantially cylindrical shape and a part of the shank 22 of the punch 21 and is also made of a material which can be magnetically attracted by the permanent magnet 32.

The portion 44 of end of the shank 22 conformed such as to engage with the projecting portion of the blocking element 23 when the blocking element 23 is fixed to the internal lateral wall 38 of the seating 31 is provided with an undercut 26, essentially constituted by a first flat surface 40 which is substantially parallel to one of the planes in which the axis of the punch 21 lies and by a second flat surface 41 proximal to the cutting head of the punch 21 and perpendicular with respect to the first surface 40.

The undercut 26 is of such dimensions with respect to the projecting portion of the cylindrical element 23 that in a predetermined angular position of the punch 21 with respect to the seating (illustrated in figures 5 and 8), the undercut 26 can couple with the cylindrical element 23 and the punch 21 can advance along the internal lateral walls 38 of the seating 31 in the direction of the permanent magnet 32. The recess 25 (figure 4) comprises an upper wall 34, distal of the cutting head of the punch 21 , and a lower wall 35, proximal of the cutting head of the punch 21 , substantially planar and perpendicular to the axis of the shank, and a lateral wall 42, substantially planar and connecting the upper wall 34 and lower wall 35.

The recess 25 is further connected to the undercut 26, i.e. it develops starting from the undercut 26 as illustrated in figures 3 and 4; further, the lower wall 35 of the recess 25 is arranged at the same height with respect to the axis of the shank as the second wall 41 of the undercut 26.

The removable blocking of the punch 21 to the shaft 30 can be performed by initially positioning the punch 21 in the seating 31 , without considering the angular orientation of the shank 22 of the punch 21 with respect to the cylindrical element 23; if follows that in the majority of cases, the upper surface 33 of the shank 22 strikes against the cylindrical element 23, see figure 4, with no coupling between the undercut 26 and the cylindrical element 23.

Notwithstanding the presence of a gap Y1 between the permanent magnet 32 and the upper surface 33 of the shank 22, the magnetic attraction force which the magnet 32 exerts on the upper surface 33 is sufficient to retain the shank 21 in the seating 31 without an operator having to hold it in this position.

At this point a first rotation of the punch 21 has to be performed, with respect to the seating 31, until the walls identifying the undercut 26 face the cylindrical element 23 and the coupling between the undercut 26 and the cylindrical element 23 (as illustrated in figures 5 and 8) is realised: the magnetic attraction force exerted by the permanent magnet 32 on the shank 22 nears the punch 21 to the permanent magnet 32, reducing the gap between the permanent magnet 32 and the upper surface 33 of the shank 22 from the gap Y1 amount to a gap Y2 amount. ln this configuration the punch 21 is arranged in the seating in the position represented in figures 5 and 8.

A further rotation of the punch 21 with respect to the seating 31 in the predetermined rotation direction W denoted in figure 8 determines insertion of a portion of the cylindrical element 23 internally of the recess 25 (as illustrated in figures 6 and 9); the coupling realised between the recess 25 and the cylindrical element 23 removably stably blocks the punch 21 with respect to the seating 31 (axial and angular blocking with respect to a rotation performed in the predetermined rotation direction W) and prevents detachment thereof. In this configuration of removable stable blocking of the punch 21 to the shaft 30, the coupling between the upper and lower walls (34, 35) of the recess 25 with the cylindrical element 23 guarantees axial blocking of the punch 21 with respect to the seating 31 , while the coupling between the lateral wall of the recess and the cylindrical element 23 prevents relative rotation of the punch 21 with respect to the seating 31 of the predetermined rotation direction W.

The recess 25 is dimensioned with respect to the cylindrical element 23 such that the joint-coupling between them is realised with a slight interference, sufficient to enable insertion of the cylindrical element 23 internally of the recess 25.

The cylindrical element 23 is advantageously fixed with respect to the permanent magnet 32 such that the upper surface 33 of the shank 22 of the punch 21 in the stable blocking configuration does not meet the lower surface 33 of the permanent magnet 32, leaving the gap Y2 between the shank 22 and the magnet 32; this enables preventing the impacts absorbed by the punch 21 during working from being transmitted to the permanent magnet 32. The punch 21 of the invention can be reliably axially stably blocked to a shaft even where there might be snagging of the punch 21 in the leather during distancing of the shaft 30, in which seating 31 the punch 21 is retained, from the leather, as already mentioned herein above. In such a case the cylindrical element 23 would met the upper wall 34 of the recess 25 of the shank 22 and exert a traction force on the punch 21 such as to detach it from the leather and retain it internally of the seating 31. The coupling between the cylindrical element 23 and the recess 25 further imposes a precise relative positioning of the punch 21 with respect to the shaft 30, which is particularly useful if the punch 21 has an asymmetrical cutting head; from a knowledge of the relative orientation of the shaft 30 with respect to a predefined angular reference it is possible to know for certain the position assumed by the punch 21 with respect to the angular reference.

Briefly, the removable blocking of the punch 21 to the shaft 30 requires only three simple operations, i.e. insertion of the punch 21 in the seating 31, such that the shank 22 abuts against the cylindrical element 23, the rotation of the punch 21 with respect to the seating 31 up until when the walls identifying the undercut 26 face the cylindrical element 23 and the punch 2 , and the rotation of the punch 21 with respect to the seating 31 in the predetermined rotation direction W up to realising the joint-coupling of the recess 25 of the shank 22 with the cylindrical element 23. The unblocking of the punch 21 from the shaft 30 requires performing a rotation in the opposite direction to the rotation direction W up to when the cylindrical element 23 disengages from the recess 25 and the walls identifying the undercut 26 face the cylindrical element 23, and the subsequent application of an opposite force to the magnetic attraction force exerted by the permanent magnet 32 on the shank 22 such as to enable extraction of the shank 22 from the seating 31.

The blocking/unblocking of the punch 21 to and from the shaft 30 is realisable by acting exclusively on the punch 21 and can be rapidly performed by an operator or by an automatic punch replacement apparatus, not shown in the figures.

The advantage of the present invention consists in having made available a punch which is removably blockable to a shaft of a machine for leather-working, which enables overcoming the drawbacks of the known-type solutions, outlined herein above, enabling a rapid and simple engagement and disengagement of the punch to/from the shaft by acting exclusively and directly on the punch, by means of operations which can be easily performed by an operator or by an automatic punch-changing device.

In a further embodiment of the punch 21, not illustrated in the figures of the drawings, the upper surface 33 of the shank 22 of the punch 21 and the recess 25 are mutually arranged such that when the undercut 26 engages with the blocking element 23 the shank 22 is advanced along the seating 31 up until the upper surface 33 of the shank 22 meets the wall of the seating 27 or the lower wall of the permanent magnet 32 such that the recess 25, by means of the rotation, can engage with the blocking element 23; thus this embodiment does not include the gap Y2 when the undercut 26 is engaged with the blocking element 23, but the upper surface 33 of the shank 22 strikes against either the upper wall of the seating 31 or the lower wall 27 of the permanent magnet. In a further embodiment of the punch 21, not illustrated in the figures of the drawings, the punch 21 does not comprise a portion of the shank made of a material which can be magnetically attracted, and no element destined to generate a magnetic force of attraction is included internally of the seating 21.

In still a further embodiment of the punch, not illustrated in the figures of the drawings, the shank of the punch can comprise a portion of magnetic material, while the seating in which it is inserted can comprise a portion of material destined to be magnetically attracted.

The insertion of the shank of the punch leads to the magnetic coupling between the portion of the seating destined to be magnetically attracted and the portion of the shank of the punch made of magnetic material, such as to retain the punch in the seating before the punch is blocked to the shaft seating by coupling between the recess and the blocking element.

The above description, made with reference to figures 3-9, defines a system 20 for blocking a leather-working punch 21 to a shaft 30 comprising: a seating 31 provided at the terminal end of a shaft 30 for receiving the shank 22 of the punch 21 ; a cylindrical permanent magnet 32 inserted in the seating 31 and fixed to the upper wall thereof, for example by gluing; a part of the shank 22 of the punch 21 made of a material which is able to be magnetically attracted by the permanent magnet 32; a blocking element 23 partially and transversally inserted in the seating 31 below the permanent magnet 32 through a through-hole 24 afforded in the external wall of the terminal part of the shaft 30 and opening into the seating 31 such that the blocking element 23 projects with respect to the internal lateral wall 38 of the seating 31 ; a portion 44 of the end of the shank 22 conformed such as to engage with the projecting portion of the blocking element 23 when the blocking element 23 is fixed to the seating 31 , such as to enable insertion of the shank 22 towards the upper wall of the seating 31 ; a recess 25 provided on the lateral wall of the shank 22 for joint-coupling, when the shank 22 inserted in the seating is rotated in a predetermined rotation direction W, with the blocking element 23 such as to axially block the punch 21 with respect to the seating 31 and prevent a further rotation in the predetermined rotation direction W.

The advantage of the present invention consists in having made available a blocking system of a punch to a shaft of an automatic leather-working machine which obviates the drawbacks in known-type solutions, outlined in the preamble hereto, enabling a rapid and simple engagement and disengagement of the punch with the shaft by acting exclusively and directly on the punch by means of operations which can be easily performed by an operator or an automatic punch- changing device.

A further advantage of the present invention consists in having defined a secure blocking system which is reliable, compact, implementable on various types of automatic machines and bearing relatively contained costs in relation to the advantages obtained. Further embodiments of the proposed blocking system, not illustrated, comprise a different arrangement of the blocking element with respect to the lateral wall of the seating, i.e. the blocking element can be fixed obliquely on the lateral wall of the seating in any orientation or parallel to the axis of the seating; these variants include the recess being dimensioned and conformed such as to couple with the blocking element in the ways described with reference to the preferred embodiment.

In still further embodiments of the blocking system, not illustrated, the blocking element is an integrated part of the seating, i.e. it is made in a single piece with the seating. In a still further embodiment, illustrated in figure 10, the blocking system is distinguished from the preferred above-described embodiment with reference to figures 3-9 due to the fact of not comprising the permanent magnet internally of the seating and not comprising a portion of the shank that is made of magnetically-attracted material.

In this variant the blocking system has the recess 25 and cylindrical element 23 reciprocally dimensioned such that the coupling realised between the recess 25 and the cylindrical element 23 enables, in the removable blocking configuration (illustrated in figure 10), the punch 21 to be axially blocked in the seating 31 and blocked with respect to a rotation in the predetermined rotation direction W, thus preventing any possible of relative axial and angular movement in the predetermined rotation direction W between the punch 21 and the seating 31.

This variant has the same advantageous technical-functional characteristics of the above-described embodiment, to which reference is made.

In a still further embodiment, illustrated in figure 1 , the blocking system is distinguished from the above-described preferred embodiment with reference to figures 3-9 in that the permanent magnet 320 is cup-shaped and identifies a seating internally thereof which is destined to receive the shank 22 of the punch 21.

The magnet 320 is fixed to the seating 31 of the shaft 30 and the blocking element 23 is an integrated part of the seating identified by the permanent magnet 320 and projects with respect thereto.

In a variant of this embodiment of the blocking system, the blocking element is constituted by a fixed cylindrical element, for example by gluing, internally of the seating identified by the cup-shaped permanent magnet 320.

The magnet 320 enables exerting a magnetically-attractive force on the upper surface of the shank 22, improving the axial blocking of the punch, but also on the lateral walls of the shank 22, advantageously increasing the torque required for disengaging the punch 21 when it is rotated in the opposite direction to the predetermined rotation direction W.

Also defined is a method for obtaining a punch, comprising stages of: pre-disposing a hollow punch 21 having a cylindrical shank 22; removing material from the shank 22 of the hollow punch 21 in order to fashion an undercut 26 such that a portion 44 of the shank 22 in which the undercut 26 is obtained can engage with a projecting portion of the blocking element 23 such that the shank 22 can move along the seat 31 ; removing material from the shank 22 of the hollow punch 21 such as to create a recess 25 conformed such as to joint-engage with the projecting portion of the blocking element 23 when the portion of the shank 22 in which the undercut 26 has been made is engaged with the blocking element 23. The stage of removing material from the shank 22 of the punch 21 in order to create an undercut 26 can comprise removing material such as to realise a first flat wall 40 substantially parallel to the axis of the punch 21 , which first flat wall 40 delimits the undercut 26.

Alternatively the stage of removing material from the shank 22 in order to realise an undercut 26 can comprise stages of: removing material such as to realise a first flat wall 40 which is substantially parallel to the axis of the punch 21 ; removing material such as to realise a second flat wall 41 which is substantially perpendicular to the first flat wall 40, the first wall 40 and the second wall 41 delimiting the undercut 26; and the stage of removing material from the shank 22 of the punch 21 such as to realise a recess 25 can comprise removing material such as to realise a lower wall 34 of the recess 25 which substantially lies on the same plane as the second flat wall 41.

This method enables simply producing a punch the technical-functional characteristics of which enable rapid and facilitated engagement/disengagement thereof from the shaft as described herein above.

The above has been described by way of non-limiting example, and any constructional variants are understood to fall within the ambit of protection of the present technical solution, as described herein above and claimed in the following.