GB2095983A

GB2095983A - Improvements in and relating to castors

Info

Publication number: GB2095983A
Application number: GB8110519A
Authority: GB
Original assignee: Guy Raymond Engineering Co Ltd
Current assignee: Guy Raymond Engineering Co Ltd
Priority date: 1981-04-03
Filing date: 1981-04-03
Publication date: 1982-10-13
Also published as: GB2095983B

Abstract

In a castor of moulded plastics a vertical bore 14 in the castor body is provided with an upwardly facing first conical thrust bearing surface 16 at its upper end and a mounting spigot 13 rotatably located in the bore is provided with a complementary second conical thrust bearing surface 22 intermediate its length, so that any load applied to the spigot is transmitted to the castor body substantially entirely through the first and second thrust bearing surfaces. The spigot is held in the body by a snap fit between rib 15 and groove 21. <IMAGE>

Description

SPECIFICATION Improvements in and relating to castors The present invention relates to a castor of the type having a body of moulded synthetic plastics material which supports a wheel or roller and a spigot which is rotatably attached in a vertical bore in the body.

It is well known to provide a castor for furniture comprising a roller or wheel mounted on a horizontal axle, the ends of which are engaged in a castor body or housing which is itself pivotally mounted on a vertical shaft or spigot, the vertical shaft or spigot being offset laterally from the roller axis so that the roller can rotate about the vertical axis of the shaft or spigot.

In this type of castor, if the body is moulded from a synthetic plastics material it has been difficult and costly to mould the bore for the spigot sufficiently accurately to eliminate play between the spigot and the castor body. The result is that the castor appears to be only loosely mounted on the spigot and there is an undesirable looseness to the whole assembly.

Various attempts have been made to overcome this problem without any real success. Roller bearings have been tried but these have proved too costly.

More accurate moulding techniques have also been tried but again this approach has proved impractical and costly.

It is therefore an object of the present invention to provide a castor assembly which is economic to manufacture but in which play between the spigot and the castor body is eliminated or at least substantially reduced.

The present invention therefore provides a castor comprising a moulded plastics body adapted to support a wheel or roller, a vertical bore in the body and a spigot rotatably located in the bore and adapted for attachment to an article on which the castor is to be mounted, wherein the bore is provided with an upwardly facing first conical thrust bearing surface at its upper end and the spigot is provided with a complementary second conical thrust bearing surface intermediate its length, the arrangement being such that any load applied to the spigot is transmitted to the castor body substantially entirely through the first and second thrust bearing surfaces.

A preferred form of the present invention will now be described with reference to the accompanying drawing which is an elevation partly in section of a castor according to the present invention.

In the drawing a castor is indicated generally at 10 which comprises a castor body indicated generally at 11, a wheel 12 and a spigot 13.

The castor body 11 is injection moulded from a suitable synthetic plastics material such as nylon and supports an axle, not shown, for the wheel 12 in a manner which is well known but which does not form a part of the present invention. Offset from the axle of the wheel 12, the body 11 is formed with a vertical bore 14 which has an annular rib 15 at its bottom end and a frusto-conical bearing surface 16 at its upper end.

The spigot 13 is a machined, steel component and comprises a shoulder 17 intermediate its length, a lower shaft 18 and an upper shaft 19. The upper shaft 19 is formed with a groove 20 adapted to receive a circlip for attaching the spigot and castor to an article of furniture in a well known manner. The lower shaft 18 is a clearance fit in the bore 14 and is formed with a groove 21 which is adapted to receive the rib 15 as a snap fit so as to retain the castor body 11 on the lower shaft 18.

The shoulder 17 has a downwardly facing frustoconical bearing surface 22 which is adapted to rest on and interface with the frusto-conical bearing surface 16 of the body 11. It will be seen that the dimensions of the lower shaft 18 in relation to the bore 14 are such that, when the rib 15 is located in the groove 21, the bearing surface 22 rests on the bearing surface 16.

In use, any downwardly directed load applied to the spigot 13, for instance the weight of an article of furniture, is tranmsitted to the castor body 11 through the bearing surfaces 22 and 16 which, at the same time, allow free rotation of the castor body 11 around the axis of the shaft 13. The wedging action between the bearing surfaces 22 and 16 ensures that there is no play between the spigot and the castor body once the castor is loaded even if the tolerances on the dimensions of the bore 14 and the castor body are such that the lower shaft 18 of the spigot is a relatively loose fit in the bore, thus ensuring that, when loaded the assembly of the castor body and the spigot are firmly secured together with no looseness or play occurring between the two components.The preferred angle of taper on the bearing surfaces 22 and 16 is 60 but this can vary within the range of 60 to 90" inclusive.

1. Acastorcomprising a moulded plastics body adapted to support a wheel or roller, a vertical bore in the body and a spigot rotatably located in the bore and adapted for attachment to an article on which the castor is to be mounted, wherein the bore is provided with an upwardly facing first conical thrust bearing surface at its upper end and the spigot is provided with a complementary second conical thrust bearing surface intermediate its length, the arrangement being such that any load applied to the spigot is transmitted to the castor body substantially entirely through the first and second thrust bearing surfaces.

2. A castor according to claim 1 wherein the castor housing comprises a raised boss forming an extension of the bore and an uppermost portion of the interior surface of the boss is configured to form the second conical thrust bearing surface.

3. A castor as in any preceding claim comprising an annular groove configured to interengage with an annular rib in the vertical bore.

4. A castor substantially as herein described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in and relating to castors The present invention relates to a castor of the type having a body of moulded synthetic plastics material which supports a wheel or roller and a spigot which is rotatably attached in a vertical bore in the body. It is well known to provide a castor for furniture comprising a roller or wheel mounted on a horizontal axle, the ends of which are engaged in a castor body or housing which is itself pivotally mounted on a vertical shaft or spigot, the vertical shaft or spigot being offset laterally from the roller axis so that the roller can rotate about the vertical axis of the shaft or spigot. In this type of castor, if the body is moulded from a synthetic plastics material it has been difficult and costly to mould the bore for the spigot sufficiently accurately to eliminate play between the spigot and the castor body. The result is that the castor appears to be only loosely mounted on the spigot and there is an undesirable looseness to the whole assembly. Various attempts have been made to overcome this problem without any real success. Roller bearings have been tried but these have proved too costly. More accurate moulding techniques have also been tried but again this approach has proved impractical and costly. It is therefore an object of the present invention to provide a castor assembly which is economic to manufacture but in which play between the spigot and the castor body is eliminated or at least substantially reduced. The present invention therefore provides a castor comprising a moulded plastics body adapted to support a wheel or roller, a vertical bore in the body and a spigot rotatably located in the bore and adapted for attachment to an article on which the castor is to be mounted, wherein the bore is provided with an upwardly facing first conical thrust bearing surface at its upper end and the spigot is provided with a complementary second conical thrust bearing surface intermediate its length, the arrangement being such that any load applied to the spigot is transmitted to the castor body substantially entirely through the first and second thrust bearing surfaces. A preferred form of the present invention will now be described with reference to the accompanying drawing which is an elevation partly in section of a castor according to the present invention. In the drawing a castor is indicated generally at 10 which comprises a castor body indicated generally at 11, a wheel 12 and a spigot 13. The castor body 11 is injection moulded from a suitable synthetic plastics material such as nylon and supports an axle, not shown, for the wheel 12 in a manner which is well known but which does not form a part of the present invention. Offset from the axle of the wheel 12, the body 11 is formed with a vertical bore 14 which has an annular rib 15 at its bottom end and a frusto-conical bearing surface 16 at its upper end. The spigot 13 is a machined, steel component and comprises a shoulder 17 intermediate its length, a lower shaft 18 and an upper shaft 19. The upper shaft 19 is formed with a groove 20 adapted to receive a circlip for attaching the spigot and castor to an article of furniture in a well known manner. The lower shaft 18 is a clearance fit in the bore 14 and is formed with a groove 21 which is adapted to receive the rib 15 as a snap fit so as to retain the castor body 11 on the lower shaft 18. The shoulder 17 has a downwardly facing frustoconical bearing surface 22 which is adapted to rest on and interface with the frusto-conical bearing surface 16 of the body 11. It will be seen that the dimensions of the lower shaft 18 in relation to the bore 14 are such that, when the rib 15 is located in the groove 21, the bearing surface 22 rests on the bearing surface 16. In use, any downwardly directed load applied to the spigot 13, for instance the weight of an article of furniture, is tranmsitted to the castor body 11 through the bearing surfaces 22 and 16 which, at the same time, allow free rotation of the castor body 11 around the axis of the shaft 13. The wedging action between the bearing surfaces 22 and 16 ensures that there is no play between the spigot and the castor body once the castor is loaded even if the tolerances on the dimensions of the bore 14 and the castor body are such that the lower shaft 18 of the spigot is a relatively loose fit in the bore, thus ensuring that, when loaded the assembly of the castor body and the spigot are firmly secured together with no looseness or play occurring between the two components.The preferred angle of taper on the bearing surfaces 22 and 16 is 60 but this can vary within the range of 60 to 90" inclusive. CLAIMS