GB2221729A

GB2221729A - Spindle unit

Info

Publication number: GB2221729A
Application number: GB8918618A
Authority: GB
Inventors: Tsutomu Nakanishi
Original assignee: CSU Ltd
Current assignee: CSU Ltd
Priority date: 1985-10-25
Filing date: 1989-08-15
Publication date: 1990-02-14
Anticipated expiration: 2006-10-16
Also published as: GB8918618D0; GB2221729B

Abstract

A spindle unit comprises a rotatable shaft (1) in which annular grooves (1a) of semicircular cross section are formed to receive balls (2) of upper and lower ball bearings. The outer races (3) of the ball bearings are defined by cylindrical sleeves with tapered surfaces which engage against the balls. The balls are spaced by annular retainers (2A) of metal or synthetic resin. Each retainer may have an axial split to facilitate assembly. <IMAGE>

Description

SPINDLE UNIT A spindle unit used for miniature motors and miniature rotors has been hitherto formed as shown in Fig. 21.

That is to say, a pair of radial ball bearings 21 and 22 are arranged above and below on the outer periphery of a shaft 20, a cylindrical spacer 23 is arranged between the respective outer races 21a and 22a of these radial ball bearings 21 and 22 to determine the respective positions of the radial ball bearings 21 and 22 with each other, the radial ball bearings 21 and 22 and the cylindrical spacer 23 are fixed within a hole H in a bearing housing 24 and such rotor 25 as a pulley, disk or turntable is fixed to the end part of the shaft 20 to rotate the shaft 20 side.

However, in the spindle unit of the above mentioned formation, in order to prevent dust or the like from entering the radial ball bearings 21 and 22 and reducing the performance, there has been used a so-called double sealing structure wherein sealing members S are arranged on both sides of balls 21c provided within the radial ball bearings. These radial ball bearings 21 and 22 have defects that they have many component parts, are complicated to assemble and are therefore high in the cost.

A rotary mechamism using the above mentioned marketed conventional radial ball bearings 21 and 22 is of a structure wherein balls 21c and 22c are contained respectively in the clearances between the inner races 21b and 22b and outer races 21a and 22a and has defects that the numbers and diameters of the balls 21c and 22c are predetermined and the balls can not be increased in the diameter, number and rigidity as required.

This invention is suggested to solve the above mentioned defects and has it as an object to provide a spindle unit wherein the radial ball bearing part formation and producing and assembling works are simplified and the cost is reduced.

Another object is to provide a spindle unit wherein the precision is improved by integrating the inner races with the shaft and working the bearing housing after assembling it.

A further object is to provide a spindle unit wherein the number of balls can be increased as required in the assembling step and any desired rigidity can be easily retained.

Another object of the present invention is to provide a spindle unit wherein there is required no such complicacy that, in the conventional radial ball bearing, in order to make the clearance between the inner race and outer race proper for the diameter of the balls, the dimensions of the outside diameter of the inner race and the inside diameter of the outer race must be measured so as to obtain a combination keeping a proper clearance; the diameter of the balls can be made somewhat larger as required and the rigidity can be increased.

Brief Description of the Drawings Fig. 1 is a schematic vertically sectioned view of the first embodiment of the present invention.

Fig. 2 is a schematic vertically sectioned view of the second embodiment of the present invention.

Fig. 3 is a schematic vertically sectioned view of the third embodiment of the present invention.

Fig. 4 is a schematic vertically sectioned view of the fourth embodiment of the present invention.

Fig. 5 is a schematic vertically sectioned view of the fifth embodiment of the present invention.

Fig. 6 is a schematic vertically sectioned view of the sixth embodiment of the present invention.

Fig. 7 is a schematic vertically sectioned view of the seventh embodiment of the present invention.

Fig. 8 is a schematic vertically sectioned view of the eighth embodiment of the present invention.

Fig. 9 is a schematic vertically sectioned view of the ninth embodiment of the present invention.

Fig. 10(a) is a schematic vertically sectioned view of the tenth embodiment of the present invention.

Fig. 10(b) is an explanatory plan view showing a shaft 1 provided around it with balls 2 incorporated in a retainer 2A.

Fig. 11 is a schematic vertically sectioned view of the eleventh embodiment of the present invention.

Fig. 12(a) is an explanatory plan view showing a shaft 1 provided around it with balls 2 incorporated in a retainer 2A.

Fig. 12(b) is a sectioned view on line A-A in Fig. 12(a).

Figs. 13 and 14 show respectively other modes of the retainer.

Fig. 15 is an explanatory view of the assembly.

Fig. 16 is a schematic vertically sectioned view of the twelfth embodiment of the present invention.

Figs. 17(1) to (3) are explanatory views of the assembly.

Figs. 18(1) to (4) are explanatory views of the thirteenth embodiment and its assembly.

Fig. 19 shows an example of applying the present invention to such roller as a tape guiding roller.

Fig. 20 shows an example of applying the present invention to a bearing for the shaft of a motor.

Fig. 21 shows a conventional example.

In the first embodiment of the present invention shown in Fig. 1, grooves 1a of a semicircular cross-section for receiving balls 2 are formed as separated from each other by cutting or grinding over the entire periphery in the upper and lower parts of the outer periphery of a columnar shaft 1 and a proper number of balls 2 are partly and rotatably received in these grooves la. The respective balls 2 are rotatably supported in contact with tapered surfaces 3a formed in parts of substantially cylindrical outer races 3.

These outer races 3 are provided around the outer periphery of the shaft 1 and outside the balls 2 and have the above mentioned tapered surfaces 3a at the inner ends. The outer peripheral surface 1b of the shaft 1 and the opposed inner peripheral surface 3b of the outer race 3 are in no contact with each other to form a gap g for preventing dust. A cylindrical sleeve 5 is provided between a pair of outer races 3 separated from each other, is to prevent the balls 2 from dropping in assembling, is fixed on the inner peripheral surface of a hole H in a bearing housing 4A, is positioned at the respective outer ends near the balls 2 and is in no contact with the outer races 3, balls 2 and shaft 1. In some case, the sleeve 5 can be fitted to the shaft 1 side.The respective outer races 3 are also fixed to the inner peripheral surface of the hsle H in the bearing housing 4A.

By the way, in case this spindle unit is to be used for the above mentioned devices, the shaft 1 is provided in the lower part with a pulley 7 and in the upper part with such rotor 6A as a pulley, disk, turntable or drum to thus form a rotary structure.

In assembling, first of all, the sleeve 5 is fixed as by pressing substantially in the middle of the hole H in the bearing housing 4A and the shaft 1 is inserted into the sleeve 5. Then, a proper number of upper or lower side balls are put into the ball~2 receiving groove la and a grease or oil is injected into the same part. Then, the outer race 3 positioned on the side of an opening of the hole H is put in through the opening to press the balls 2 with the tapered surface 3a and is fixed in a proper position on the inner peripheral surface of the bearing housing 4. Then, the balls 2 and outer race 3 on the other side may be put in in the same manner. 3y the way, the rotor 6A and pulley 7 are properly fitted to the shaft 1.

In the above mentioned assembling step, before the rotor 6A and pulley 7 are fixed, the rotation precision of the shaft 1 can be confirmed and, by finely adjusting the position of the outer race 3, the clearance from the balls 2 can be easily adjusted and a favorable rotary performance can be obtained.

In using it, the inner peripheral surface 3b of the outer race is so close to the outer peripheral surface 1b of the shaft 1 that the entry of dust into the ball part can be prevented by this dust preventing fine gap g so as to be very little.

In the second embodiment of the present invention shown in Fig. 2, the outer races 3 are not fixed but are slidably fitted to the inner peripheral surface of the hole H in the bearing housing A and are fixed by outer race pressers 8 respectively provided outside the outer races 3 and fixed to the inner peripheral surface. In such case, there is a feature that both or either of the upper and lower outer race pressers 8 are or is made of such elastic member as rubber so as to give an initial pressure to the outer races 3 in contact with the balls 2 and to prevent a backlash fróm being caused by the wear of the ball rolling surfaces.

The other formation is the same as in the first embodiment.

In the third embodiment of the present invention shown in Fig. 3, such resilient member as a spring 9 is provided as contracted between the outer race 3 and outer race presser 8 so as to give an initial pressure to the outer race 3.

In the fourth embodiment of the present invention whown in Fig. 4, either of the outer race pressers is of an outer race adjusting screw 8 structure and a threaded part 4a to be screwed with the threaded part of the outer race presser is formed on the inner peripheral surface of the bearing housing 4A so that, by this outer race adjusting screw 8A for adjusting the clearance, the position of the outer race 3 may be adjusted and the clearance between the ball 2 and outer race 3 may be adjusted. By the way, the other outer race presser 8 is fixed to the bearing housing 4A.

The fifth embodiment of the present invention is shown in Fig. 5. In the first to fourth embodiments, two ball parts are provided but, in the subsequent embodiments (shown in Figs. 5 to 9), the ball part is provided on only one side.

That is to say, in the fifth embodiment, the groove la of a semicircular cross-section is formed in a part of the outer periphery of the columnar shaft 1 and the balls 2 are rotatably held by this groove 1a and the tapered surface 3a of the outer race 3 fixed to the inner peripheral surface of the bearing housing 4A. 3y the way, the cylindrical sleeve 5 to be fixed to the inner peripheral surface of the bearing housing 4A is provided near the balls 2 and the tapered surface 3a of the outer race 3. In such case, the dust preventing gap g is formed between the inner peripheral surfaces of the outer race 3 and sleeve 5 and the outer peripheral surface of the shaft 1.

In assembling, within the bearing housing 4A, the sleeve 5 is fixed, then the shaft is inserted and a proper number of balls 2 are put in through the other opening and are positioned in the groove la.

In such case, the balls 2 are prevented by the sleeve 5 from dropping. Then, the outer race 3 may be put into the bearing housing 4A from the tapered surface 3a side to be fixed in a proper position.

By the way, the shaft 1 may be supported in the other part, as required, by an ordinary radial bearing, plane bearing or pivot bearing.

The sixth embodiment of the present invention shown in Fig. 6 is different from the fifth embodiment in respect that a sleeve 4A' extending toward the shaft 1 is formed integrally with the inner peripheral surface of one end part of the bearing housing 4A.

The other formation is the same.

In the seventh embodiment of the present invention shown in Fig. 7, the outer race 3 is loosely fitted within the bearing housing 4A and is fixed by the outer race presser 8 made of an elastic member arranged outside the outer race 3 so as to give an initial pressure by the elasticity of the outer race presser 8 to prevent a backlash from being caused by the wear of the ball rolling surface. The other formation is the same as in the fifth embodiment.

The eighth embodiment of the present invention shown in Fig. 8 is different from the seventh embodiment in respect that the outer end of the outer race 3 loosely fitted within the bearing housing 4A and the inner end of the outer race presser 8 of a nonelastic member fixed within the bearing housing 4A are separated from each other and such resilient member 9 as a spring is set as contracted between them so as t~ give an initial pressure to the outer race 3. It is needless to say that, in such case, the outer presser 8 is not particularly required to be of an elastic member.

In the ninth embodiment of the present invention shown in Fig. 9, the outer race adjusting screw 8A is provided in the inner peripheral part of the bearing housing 4A outside the outer race 3 to thereby make it possible to adjust the clearance.

In this case, too, the sleeve 5 for preventing the balls from dropping may be fitted to the shaft 1 side.

The tenth embodiment of the present invention is shown in Fig. 10. In the above described embodiments, no means of particularly holding the balls 2 arranged around the shaft 1 is provided and therefore, in the rotation above the medium speed, the balls will contact with each other to be likely to generate noises and mechnical losses.

In this tenth embodiment, the valls are held at a proper spacing from each other to prevent the balls from contacting with each other and to control the generation of noises and mechanical losses to be minimum.

That is to say, the balls 2 are held through a ring-shaped retainer 2A so as to be positioned between the groove Ia of the shaft 1 and the tapered surface 3A of the outer race. By the way, in such case, a retainer 2A escaping part 3c is formed in the outer sleeve 3.

In assembling, for example, first of all, a proper number of balls are put at intervals into the retainer 2A within a jig (not illustrated). This jig is made to have a magnetic force or attracting force so that the balls may be incorporated while being prevented from dropping.

On the other hand, the sleeve 5 is fixed as by being pressed substantially in the middle within the bearing housing and the shaft 1 is inserted into the sleeve 5. Then, the balls 2 held at a spacing from each other in the upper or lower retainer 2A are put into the groove 1a and a grease or oil is injected into such part. Then, the outer race 3 to be positioned on the side of the opening of the bearing housing A is put through the same opening to press the balls 2 with the tapered surface 3a and is fixed in a proper position on the inner peripheral surface of the bearing housing 4A. Then, the balls 2 and outer race 3 on the other side are put in in the same manner and the rotor 6A and pulley 7 may be fixed to the respective end parts of the shaft 1 as shown in Fig. 1.

In the eleventh embodiment of the present invention, the sleeve 5 for preventing the balls 2 from dropping in the above described tenth embodiment is not required so that the assembly may be that much easy.

In such case, the retainer 2A is ring-shaped particularly as shown in Figs. 12(a) and (b) and is made of such resilient member as of a synthtic resin or metal. The balls 2 are held by this retainer 2A through ball receiving parts consisting of holes arranged at proper intervals and having a diameter substantially equal to or somewhat smaller than the diameter of the ball. This retainer 2A has such clearance through which the balls 2 will not come out between it and the balls and the balls 2 are forced into the retainer.

Otherwise, the retainer 2A may be such ordinary one as is shown in Fig. 13 or may be made of a resilient member having a cut A formed in a part as shown in Fig. 14 so as to be easily variable in the inside diameter.

In assembling, as shown in Fig. 15(1), the retainer 2A with the balls incorporated in advance is pushed onto the outer periphery of the shaft 1. In such case, the retainer 2A will be pushed to expand somewhat outward as shown by the arrows by the shaft 1 and balls 2 in contact with the shaft. That is to say, the retainer 2A is naturally larger in the diameter than the shaft 1 but, in the case of fitting the balls 2 to the outer periphery of the shaft, will be of such diameter as will be pushed to expand somewhat outward against the resilient force caused by the material.

As shown in Fig. 15(2), when the retainer 2A is pushed in to reach the groove la, the retainer will contract so much that the balls will not drop but will be respectively fitted in the groove la. Then, when the assembly is inserted into the bearing housing 4A and the outer races 3 are respectively inserted from outside, a spindle unit will be able to be assembled without using any sleeve.

In using it, the inner peripheral surface 3b of the outer race 3 is so close to the outer peripheral surface Ib of the shaft 1 that the entry of dust or the like will be able to be prevented by the dust preventing fine gap g to be minimum.

The twelfth embodiment of the present invention shown in Fig. 16 has a feature that the distance between a pair of grooves 1a formed on the outer periphery of the shaft 1 is narrow and the balls 2 are provided correspondingly in two steps in a retainer 2A'. The fundamental material and formation of the retainer 2A' are the same as in the above described embodiments.

In assembling, as shown in Fig. 17(1), first of all, the balls incorporated in the retainer 2A' are contacted with the outer periphery of the shaft and are pushed down toward the grooves la as indicated by the arrow.

Then, as shown in Fig. 17(2), when the balls 2 first positioned on the lower side in the drawing reach the upper groove 1a, the balls 2 will be fitted in the groove 1a by the resiliency of the retainer 2A'. At this time, the ball part on the upper side will remain expanded outward.

When the balls 2 in two upper and lower steps are further pushed down, as shown in Fig. 17(3), the balls 2 will be fitted in the respective grooves 1a so as to be fitted on the outer periphery of the shaft 1.

In the thirteenth embodiment of the present invention shown in Fig. 18, the distance between a pair of grooves formed on the outer periphery of the shaft 1 is so narrow that no sleeve for preventing the balls from dropping is required, assembled parts are decreased and assemblability is improved.

That is to say, in assembling, first of all, as shown in Fig. 18(1), the shaft 1 is inserted into a hollow part provided with one outer race 3 in one end part of the bearing housing 4A and is arranged in a proper position. Then, in the illustrated state, a proper number of balls 2 are inserted from the lower side. In such case, a ball receiving jig 6' is used to prevent the balls 2 from dropping. Thus, the balls 2 will be rotatably supported by the respective ball rolling surfaces of the groove 1a and the tapered surface 3a of the outer race 3. By the way, the outer race 3 will be fixed in a position adapted to support the balls 2.

Then, as shown in Fig. 18(2), the above mentioned assembly is turned upside down on the reverse side and a proper number of balls 2' are inserted between the bearing housing 4A and shaft 1 from the upper side.

Then, as shown in Fig. 18(3), the other outer race 3' is inserted into the bearing housing 4A and, as shown in Fig. 18(4), the balls 2' are rotatably supported by the tapered surface 3a' of this outer race 3' and the groove la' and the outer race 3' is fixed in a proper position so that a light thin short spindle unit may be assembled. That is to say, in the spindle unit of the present invention, the distance between the grooves la and 1a' is so short that no sleeve is required, therefore the weight is light, the balls 2 and 2' are held directly by the shaft 1 and the outer races 3 and 3' provided on the outer periphery of the shaft 1 and therefore the type is thin.

By the way, in using it, the inner peripheral surfaces 3b and 3b' of the respective outer races 3 and 3' are so close to the outer peripheral surface 1b of the shaft 1 that the entry of the dust or the like into the ball parts will be able to be prevented by this dust preventing fine gap g. (See Fig. 18(4).) In the fourteenth embodiment of the present invention shown in Fig. 19, the structure of the rotating part of the above mentioned spindle unit is applied to such roller as a tape guiding roller.

That is to say, in the drawing, the reference numeral 1 represents a substantially columnar shaft, a pair of grooves la for receiving balls are formed as separated from each other as by cutting in the upper and lower parts of the outer periphery of this shaft 1 and a proper number of spherical balls 2 are partly and rotatably received in each of these grooves. The reference numeral 3 represents a cylindrical outer race provided above or below, tapered at the inner end and expanding in the diameter successively inward.

These tapered surfaces 3a contact the balls 2 to hold the balls provided above and below. The inner peripheral surface 3b is in no contact with the outer peripheral surface 1b of the shaft 1 to form a dust preventing gap g. A cylindrical bearing housing 4 is provided on the outer periphery of the outer race 3. The outer peripheral surface of the outer race 3 is fixed to the inner peripheral surface of this bearing housing 4.

A cylindrical sleeve 5 is provided between a pair of outer races 3 separated from each other, is to prevent the balls 2 from dropping in assembling, is fixed on the outer peripheral surface to the inner peripheral surface of the bearing housing 4, is positioned at the outer ends near the balls and is in no contact with the outer races 3, balls 2 and shaft 1. By the way, the reference numeral 6 represents a pulley fixed to the upper end part of the shaft 1 and in no contact with the bearing housing 4 and outer races 3. The reference numeral 7 represents a pulley having a fitting part 7a for fitting to a chassis (not illustrated) or the like and fixed to the lower end part of the shaft 1.

In assembling, first of all, the sleeve 5 is fixed as by being pressed substantially in the middle within the bearing housing 4 and the shaft 1 is inserted into the sleeve 5. Then, a proper number of balls 2 on the upper or lower side are put into the groove la and a grease or oil is injected into the same part. Then, the outer race 3 positioned on the opening side of the bearing housing 4 is put in through the same opening to press the balls 3 with the tapered surface 3a and is fixed in a proper position on the inner peripheral surface of the bearing housing 4.

Then, the balls 2 and outer race 3 on the other side may be put in in the same manner and the pulleys 6 and 7 may be fixed to the respective end parts of the shaft 1.

By the way, in te above mentioned assembling step, before the pulleys 6 and 7 are fixed, the rotation precision of the bearing housing 4 can be confirmed and, by finely adjusting the position of the outer race 3, the clearance between the outer race 3 and balls 2 can be easily adjusted, a favorable rotation performance can:be obtained and thus the bearing housing 4 can be rotatably supported with respect to the shaft 1. By the way, the inner peripheral surface 3b of the outer race 3 is so close to the outer peripheral surface of the shaft 1 that the entry of dust or the like into the ball parts can be prevented by this dust preventing fine gap g to be minimum.

In the fifteenth embodiment of the present invention shown in Fig. 20, the formation of the rotating part of the above mentioned spindle unit is applied to the bearing of the shaft 1 of a motor M.

That is to say, grooves la for receiving the balls 2 are formed in predetermined positions on the outer periphery of the shaft 1. Further, substantially ring-shaped ball receiving collars 10 are provided respectively inside the grooves la on the outer periphery of the shaft 1. Each outer race 3 is provided in a position outside the groove la, is in no contact with the shaft 1 and is separated from and opposed to the ball receiving collar 10. A tapered surface 3a expanding in the diameter successively inward is formed inside each outer race 3. The balls 2 arranged on the outer periphery of the shaft 1 are received by the ball receiving collars 10, grooves 1a and tapered surfaces 3a. The bearings of the rotary shaft of the motor X, that is, the shaft 1 are formed also of these members.

By the way, in the drawing, the reference numeral 11 represents a bottomed cylindrical bearing housing in which a hole 11a is formed in the center of the bottom, the shaft 1 is inserted on one end side through the hole lia to project out and the outer race 3 is fixed on the outer peripheral surface to the peripheral surface side of the hole 11a. The reference numeral 12 represents a disk-shaped bracket provided in the opening part of the bearing housing 11 and having the same hole 11a formed in the center and the shaft 1 supported on the other end side through a bearing.

In such case, it is preferable to make a fine gap between the inner peripheral surface of each outer race 3 and the opposed outer peripheral surface of the shaft 1 to have a dust preventing function.

By the way, as well known, a commutåtor and rotor R are provided on the outer periphery of the shaft 1 within the bearing housing 11, a stator S or the like is provided on the inner peripheral surface side of the bearing housing 11 and a motor M having the same bearing structure as of the rotating part of the spindle unit is formed.

According to the present invention formed as in the above, no radial ball bearing of a costly double sealing structure is required, the number of parts reduces to be fewer than in the spindle unit using the above mentioned conventional radial ball bearings and the cost can be that much reduced.

The inner race and shaft can be made integral and the bearing housing can be worked after the assembling to improve the precision.

Further, the number of balls can be increased as required in the assembling step and the required rigidity can be easily obtained.

There is required no such complicacy that, in the conventional radial ball bearing, in order to make the clearance between the inner race and outer race proper for the diameter of the balls, the dimensions of the outside diameter of the inner race and the inside diameter of the outer race must be measured so as to obtain a combination keeping a proper clearance. The diameter of the balls can be made somewhat larger as required and the rigidity can be increased.

Claims

1. A spindle unit comprising: a rotatable shaft formed to be columnar and having grooves made semicircular in the cross-section for partly receiving balls and formed on the outer periphery, outer races provided as separated from and opposed to each other on the outer periphery of said shaft, each having a tapered surface which contacts and holds said balls with said groove, formed to be substantially ring-shaped as a whole and having said tapered surface formed in a part and a bearing housing fixing said outer races.

2. A spindle unit according to claim 1 wherein a plurality of balls arranged between said shaft and outer race are held by a retainer.

3. A spindle unit according to claim 1 wherein said groove for partly receiving the balls is formed on only one side of the outer periphery of the shaft, said outer race having the tapered surface is arranged outside said groove and the balls are provided between said groove and tapered surface.

4. A spindle unit comprising a rotatable shaft, a bearing housing for said shaft, and two axially spaced ball bearings, each ball bearing comprising an inner race defined by an annular groove of semicircular cross-section in the outer periphery of the shaft and an outer race defined by a sleeve member received between the bearing housing and the shaft.

5. A spindle unit substantially as herein described with reference to any of Figures 1 to 20 of the accompanying drawings.

Amendments to the claims have been filed as follows 1. A spindle unit comprising, a housing having a through-hole, a rotatable shaft extending through the through-hole and having a groove, of semi-circular cross-section, formed in a surface thereof, a plurality of balls disposed in the groove, a substantially ring-like, outer ball race which fits within the through-hole, in spaced relationship to the shaft, to provide a clearance between the shaft and the outer ball race, and has a tapered, ball-receiving surface which contacts the balls to hold them in the groove, and a retainer for holding the balls apart from each other in the groove.

2. A spindle unit as claimed in claim 1, including a pair of said grooves formed in a surface of the shaft, a respective plurality of balls disposed in each groove, a pair of said substantially ring-like outer ball races, the tapered, ball-receiving surface of each ball race contacting the balls in a respective one of the grooves to hold them in that groove, and wherein the retainer holds the balls of each plurality apart from each other in the respective grove.

3. A spindle unit as claimed in claim 2, wherein the retainer is a common retainer for holding the balls of each said plurality apart from each other in the respective groove.

4. A spindle unit as claimed in any one of claims 1 to 3, wherein the retainer comprises a tube which fits around the shaft and is made of a resilient material, the tube being formed with spaced circumferentially disposed holes, each locating a respective ball.

5. A spindle unit as claimed in claim 4, wherein the tube has a slit along its length.

6. A spindle unit substantially as herein described with reference to Figures 11 to 17 of the accompanying drawings.