FIELD OF THE INVENTION

The present invention relates to a screw threaded member and to a method of providing a member with a screw threaded portion. The invention has application in providing an otherwise unthreaded member with a screw threaded portion and for repairing previously threaded members.

BACKGROUND OF THE INVENTION

It is known to provide a shaft which has a screw threaded portion and to repair the screw threaded portion by grinding the threaded portion, applying material to the ground portion by welding, and forming a fresh screw threaded portion on the welded portion.

However, high temperatures generated during welding can cause damage to the shaft.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a screw threaded member comprising: a shaft; a screw threaded collar disposable on the shaft; means for restricting rotation of said collar relative to the shaft; and means for restricting reciprocal movement of said collar relative to the shaft.

In one embodiment, the screw threaded collar comprises at least two collet portions arranged such that when the collet portions are disposed on the shaft portion, an externally screw threaded collar is defined.

Each of the collet portions may include a groove arranged such that when the collet portions are disposed on the shaft, an 0-ring is receivable in the grooves so as to retain the screw threaded collar on the shaft.

In one embodiment, the shaft is provided with a first shaft portion, a second shaft portion, and a third shaft portion between the first and second shaft portions of reduced diameter relative to the first and second shaft portions, and the screw threaded collar portion is arranged such that at least part of the screw threaded collar is disposable on the third shaft portion so as to thereby restrict reciprocal movement of the collar relative to the shaft.

In one arrangement, the screw threaded collar is arranged such that the screw threaded collar is wholly disposable on the third shaft portion. In an alternative arrangement, the screw threaded collar comprises a stepped portion disposable on the third shaft portion.

In an alternative embodiment, the screw threaded collar comprises a sleeve.

In this embodiment, the shaft may include a first shaft portion, a second shaft portion and a third shaft portion between the first and second shaft portions of reduced diameter relative to the first and second shaft portions, and the screw threaded member may further comprise a collet, the sleeve being disposable on the first shaft portion and the collet being disposable on the third shaft portion so as to restrict reciprocal movement of the sleeve. An O-ring may be provided to retain the collet relative to the third shaft portion. The means for restricting rotation of the screw threaded collar relative to the shaft may comprise adhesive.

In addition, or alternatively, the screw threaded member may further comprise a pin member, the shaft may be provided with at least one aperture, and the screw threaded collar may be arranged such that the pin member is receivable in the at least one aperture through the collar, the pin member cooperating with the collar so as to restrict rotation of the collar relative to the shaft. The pin member may be a roll pin.

In one arrangement, the screw threaded collar is an externally screw threaded collar.

The means for restricting reciprocal movement of the screw threaded collar relative to the shaft may comprise a narrower diameter shaft portion in which a portion of the collar is received and relatively larger diameter shaft portions longitudinally on either side of the narrower diameter shaft portions.

In accordance with a second aspect of the present invention, there is provided a method of providing a member with a screw threaded portion, said method comprising the steps of: providing a shaft; providing a screw threaded collar; disposing the screw threaded collar on the shaft; restricting rotation of said collar relative to the shaft; and restricting reciprocal movement of said collar relative to the shaft. - A -

In accordance with a third aspect of the present invention, there is provided a collar and shaft combination comprising: a shaft; a collar disposable on the shaft; means for restricting rotation of said collar relative to the shaft; and means for restricting reciprocal movement of said collar relative to the shaft.

In accordance with a fourth aspect of the present invention, there is provided a method of providing a shaft member with a collar, said method comprising the steps of: providing a member having a shaft; providing a collar; disposing the collar on the shaft; restricting rotation of said collar relative to the shaft; and restricting reciprocal movement of said collar relative to the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of a shaft of a screw threaded member in accordance with an embodiment of the present invention; Figure 2 is a diagrammatic view of a screw threaded member in accordance with an embodiment of the present invention incorporating the shaft shown in Figure 1; Figure 3 is a diagrammatic view of a shaft and a screw threaded collar portion of a screw threaded member in accordance with an alternative embodiment of the present invention; Figure 4 is a diagrammatic view of a shaft and a collar portion of a screw threaded member in accordance with a further alternative embodiment of the present invention; Figure 5 is a diagrammatic view of a shaft and a collar portion of a screw threaded member in accordance with a further alternative embodiment of the present invention; and Figure 6 is a sequence of diagrammatic views of a shaft and collar portion of Figure 5 showing the steps of disposing the collar portion on the shaft.

DESCRIPTION QF AN EMBODIMENT OF THE PRESENT INVENTION

Referring to Figures 1 and 2 of the drawings, there is shown a screw threaded member 10 which includes a shaft 11 having a first shaft portion 12, an end collar 14, a second shaft portion 16 of reduced diameter relative to the first shaft portion 12 and the end collar 14 , and a bearing 18 which facilitates rotation of the second shaft portion 14 relative to the first shaft portion 12. Two apertures 20, only one of which is shown in Figure 1, are formed in the second shaft portion 16 at diametrically opposite locations.

As shown more particularly in Figure 2, the screw threaded member 10 also includes a collar portion, in this example in the form of a screw threaded collet 22 having a first collet portion 24 and a second collet portion 26. Each of the first and second collet portions 24, 26 is of generally half-cylindrical shape and the first and second collet portions 24, 26 are arranged such that when the first and second collet portions 24, 26 are disposed around the second shaft portion 16, a generally cylindrical shaped collet 22 is defined. It will be understood that the first and second collet portions 24, 26 are also arranged such that when the collet portions 24, 26 are disposed on the second shaft portion 16, an externally screw threaded portion is defined which is capable of engaging with a corresponding internally screw threaded portion of a retaining member, such as an internally screw threaded portion of a retaining nut.

It will also be understood that when the screw threaded collet 22 receives a corresponding internally screw threaded member such as a nut, the first and second collet portions 24, 26 are held relative to the shaft 11 by the nut.

It will also be understood that since the second shaft portion 16 is of reduced diameter relative to the bearing 18 and the end collar 14 and is disposed between them, the screw threaded collet 22 is restricted from moving reciprocally relative to the shaft 11.

In order to restrict the screw threaded collet 22 from rotating relative to the shaft 11, each of the first and second collet portions 24, 26 is provided with a notch portion 29. The notch portion 29 collectively receive and contact a roll pin 28 which during use passes through the apertures 20.

It will be understood that while the screw threaded collet 22 is retainable on the second shaft portion 14 using an internally screw threaded member such as a nut, an adhesive may also be provided to fix the first and second collet portions 24, 26 onto the second shaft portion 14.

It will be appreciated that in this way it is possible to provide a previously unthreaded shaft with a screw threaded portion and to provide a damaged previously threaded shaft with a fresh screw threaded portion. In order to repair a damaged threaded shaft, a screw threaded portion of an existing screw threaded shaft is first ground using any suitable device in order to remove the damaged screw threaded portion, and apertures 20 are formed in the ground region. The ground region forms the reduced diameter second shaft portion 16. The first and second collet portions 24, 26 are then disposed on the ground region so as to define a screw threaded collet 22, and the roll pin 28 is inserted into the apertures 20 to restrict rotation of the screw threaded collet 22 relative to the shaft 11.

An alternative screw threaded member is shown in Figure 3, the alternative screw threaded member including an alternative shaft 30 and an alternative screw threaded collet 31.

The shaft 30 includes first and second shaft portions 32 and 34 respectively and a third shaft portion 36 of reduced diameter relative to the first and second shaft portions 32, 34 and disposed between the first and second shaft portions 32, 34.

The screw threaded collet 31 includes a first collet portion 38 and a second collet portion 40. The first and second collet portions 38, 40 are similar to the first and second collet portions 24, 26 of the screw threaded member 10 shown in Figure 2 in that the first and second collet portions 32, 34 are of generally half-cylindrical configuration. However, the first and second collet portions 38, 40 shown in Figure 3 are each provided with an outwardly facing groove 42 arranged to receive an O-ring 44 during use, the 0-ring serving to retain the screw threaded collet 31 on the third shaft portion 36 during use.

As with the embodiments shown in Figures 1 and 2, the first and second collet portions 38, 40 are disposable on the third shaft portion 36 and restricted from moving reciprocally relative to the shaft 30 by the adjacent enlarged diameter first and second shaft portions 32, 34 on either side of the third shaft portion 36.

In this example, the screw threaded collet 31 is prevented from rotating relative to the shaft 30 by applying adhesive between the screw threaded collet 31 and the third shaft portion 36. However, it will be understood that other arrangements for restricting rotation of the screw threaded collet 31 relative to the shaft 30 are envisaged.

A further alternative screw threaded member is shown in Figure 4, the further alternative screw threaded member including an alternative shaft 50 and an alternative screw threaded collet 51.

The shaft 50 includes a first shaft portion 52, second and third shaft portions 54 and 56 respectively of reduced diameter relative to the first shaft portion 52, and a fourth shaft portion 58 of reduced diameter relative to the second and third shaft portions 54, 56 and disposed between the second and third shaft portions 54, 56.

The screw threaded collet 51 includes a first collet portion 60 and a second collet portion 62. The first and second collet portions 60, 62 are similar to the first and second collet portions of the embodiment shown in Figure 3 in that the first and second collet portions 60, 62 are of generally half-cylindrical configuration and each of the first and second collet portions 60, 62 is provided with an outwardly facing groove 63 arranged to receive an O-ring 64 during use. Each of the first and second collet portions 60, 62 shown in Figure 4 also includes a stepped portion 66 extending around an inwardly facing surface of the first and second collet portions 60, 62. The arrangement is such that the stepped portion 66 fits in the fourth shaft portion 58 when the first and second collet portions 60, 62 are disposed on the first, second and third shaft portions 54, 56, 58 and thereby restricts reciprocal movement of the screw threaded collet 51 relative to the shaft 50.

In this example, the screw threaded collet 51 is prevented from rotating relative to the shaft 50 by applying adhesive between the screw threaded collet 51 and the first, second and third shaft portions 54, 56, 58. However, it will be understood that other arrangements for restricting rotation of the screw threaded collet 51 relative to the shaft 50 are envisaged.

A still further alternative screw threaded member is shown in Figures 5 and 6, the alternative screw threaded member including an alternative shaft 70 and an alternative screw threaded collet 82.

The shaft 70 includes a first shaft portion 72, second and third shaft portions 74 and 76 respectively of reduced diameter relative to the first shaft portion 72, a fourth shaft portion 78 of reduced diameter relative to the second and third shaft portions 74, 76 and disposed between the second and third shaft portions 74, 76, and an extension portion 80 of reduced diameter relative to the third shaft portion 76.

The sleeve 82 includes a screw threaded portion 84 and a non-threaded portion 86, the sleeve 82 being disposable on the second shaft portion 74 such that the non-threaded portion 86 locates adjacent the fourth shaft portion 78.

The screw threaded member 70 further includes first and second collet portions 88 and 90 which are of a diameter about the same as the diameter of the non-threaded portion 86. The first and second collet portions 88 and 90 are disposable on the fourth shaft portion 78. The first and second collet portions in combination with the first shaft portion 72 restrict reciprocal movement of sleeve 82 during use as will be described further below.

Figure 6 shows a sequence of steps in the installation of sleeve 82 and collet portions 88 and 90 on the shaft 70.. The sequence starts at A with the shaft 70 free of the sleeve 82 and collect portions 88 and 90. At B the sleeve 82 slides over shaft portion 72 and abuts surface 100 of a step between the first and second shaft portions 72, 74.

In step C collet portions 88 and 90 are disposed over the fourth shaft portion 78 so that they sit within the space created by a stepped interface between the second shaft portion 74 and the fourth shaft portion 78 and a stepped interface between the fourth shaft portion 78 and the third shaft portion 76. The collet portions 88 and 90 are shaped to form a step defined by a main body 90 of the collet portions 88 and 90 and a narrowed portion 98 which projects from the main body 90. The distance of extension of the narrowed portion 98 is substantially the same as the width of O-ring 91. The diameter of the narrowed portion 98 is less than the inner diameter of the sleeve 82. A gap 102 is formed between the main body 90 of the collet portions 88 and 90 and a surface 94 of the collar due to the narrowed radius of portion 98.

In step D the sleeve 82 is slid back towards the collet portions 88 and 90 so that it substantially closes the gap 102 and partially rides over the narrowed portion 98 of the collet portions 88 and 90. This retains the collet portions 88 and 90 in place. In doing so the surface 94 of the sleeve 82 sits closely adjacent to or abuts the main body 90 of the collet portions 88 and 90. By sliding the sleeve 82 towards the collet portions 88 and 90 a gap 104 is formed between a surface 92 of the sleeve 82 and - li ¬

the step surface 100. The width of the gap 104 is substantially the same width as the gap 102.

In step E, 0-ring 91 is then disposed within the gap 104, that is between the step surface 100 and the surface 92 of the sleeve 82. The 0-ring 91 and the collet portions 88 and 90 restrict reciprocal movement of the sleeve 82 relative to the shaft 72.

In this example, sleeve 82 is prevented from rotating relative to the shaft 70 by applying adhesive between the sleeve 82 and the second shaft portion 74. However it will be understood that other arrangements for restricting rotation of the sleeve 82 relative to the shaft 70 are envisaged. Such an arrangement may include a slot and projecting key arrangement.

It can be seen that the sleeve 82 has screw threaded portion 84 and the non-threaded portion 86. The non- threaded portion 86 may be used to receive a seal. Sometimes the non-threaded portion 86 becomes damaged and it is desirable to replace the non-threaded portion 86 rather than the threaded portion 84. The present invention provides a method of replacing the non-threaded portion 86 which may or may not be replaced with the threaded portion 84.

In the event that the non-threaded portion 86 only is to be replaced, it may be ground away to form the second shaft portion 74. The threaded portion (if any) may be disposed on the first shaft portion 72. The sleeve 82 need not have a screw threaded portion 84.

It is also noted that the threaded portion may be internally threaded instead of externally threaded. In the claims of this application and in the description of the invention, except where the context requires otherwise due to express language or necessary implication, the words "comprise" or variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.