BACKGROUND TO THE INVENTION Diamond wire is fast becoming the most favoured tool for cutting stone and cementitious material as well as brick, mortar and other abrasive materials. This is because, compared to traditional methods such as blasting and mechanical breaking of rock in quarries and imploding of building structures, diamond wire cutting shows low production costs as well as reduction of waste. In this specification"diamond wire"is to be understood to include wire carrying metal ferrules in which is embedded particles of cubic boron nitride to replace the diamonds of diamond wire.

Diamond wire can be used for profile cutting to a high degree of accuracy which is highly desirable though this accuracy is dependant on the size of the cutting wire or ferrules fitted to wire cables. Presently the size of wire is limited to about 6 mm diameter.

These diamond wires are made by electro-deposition of diamond grit onto steel cables or by sintering, brazing or electroplating diamonds onto small ferrules known as"beads"which are subsequently secured to wire cables. The former process is difficult and expensive and the latter has the size limitation above referred to.

Also, the location of the beads on a cable has been effected by impregnating the cable between the beads with plastics material. Alternatively loaded springs, spacers and pressers have been used.

OBJECT OF THE INVENTION It is an object of the present invention to provide a diamond wire that utilises beads and can have a diameter appreciably below 6mm.

SUMMARY OF THE INVENTION According to this invention there is provided a bead for diamond wire comprising an electroformed metal sleeve with diamond grit embedded therein.

The invention also provides a method of making a diamond wire comprising electroforming a carrier filament along its length with a metal in a layer of diamond grit to embed the grit in the metal and subsequently removing the filament, dividing the resultant sleeve into beads and attaching the beads at intervals along a wire cable core.

Alternatively the filament may be coated only at spaced intervals along its length by insulating the filament against electroforming so the beads are provided at intervals along the length of the filament between the insulating material.

Further features of this invention provide for the metal deposited to be nickel and for the filament to be a suitable metal wire, and for the metal wire to be dissolved or otherwise removed from the electroformed beads. Also the beads may be formed by multilayering the diamond grit into the electroformed metal.

The invention further provides for the beads to be secured on a wire cable core to form a diamond wire or to be retained in their separated positions on the cable by means of spacers or rubber or rubber-like material moulded onto the wire cable.

A still further feature of this invention provides for the complete beads to have a diameter of less than 6mm and for the wire cable to be of high quality and if required to be stainless steel wire.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features of this invention will become apparent from the following description of one embodiment wherein reference will be made to the accompanying drawings in which: FIG 1 shows an aluminium filament prepared for electroformation ; FIG 2 an individual bead; and FIG 3 a length of completed diamond wire.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS As illustrated a bead (1) for a diamond wire (2) is prepared by the known electroformation process of a metal to entrap and embed diamond grit (3) therein.

A core (4) for the deposition process is prepared by coating a length of filament on which metal may be formed electrolytically with plastics material (5) to bind to the surface of the filament. The sleeve so formed is removed from the filament at

spaced intervals (6) over lengths which will equal the lengths of the required beads (1). Alternatively, individual sleeves (5) of the required length and made from suitable plastics material can be threaded onto the filament and heat-shrunk in position at the desired intervals.

The diameter of the filament is chosen to be slightly greater than that of the wire cable (7) which is to be formed into a diamond wire.

The filament (4) coated at intervals as above described is connected into electroplating equipment, in well known manner, for the forming of nickel or other suitable metal thereon in a bed of diamond grit. This results in separate beads of metal with diamond grit embedded therein being formed on the sleeve filament.

This process can be repeated to form a multilayered formation of diamond grit.

The coated filament is then cut in the lengths of the plastic shielding (5) and the filament core then removed from the beads.

It has been found favourable to have the electroformation continuous along the metal filament and the resultant sleeve cut by water jet into separate pieces, which form beads, from which the filament can be readily removed. Also the preferred filament is aluminium, which can be dissolved from the beads with caustic soda. The removal results in freeing the deposited nickel or other selected metal as separate beads with diamond grit embedded therein.

The beads are then threaded onto a stainless steel cable and located at desired spaced intervals on the cable. The diamond wire is thus provided and can, where required, be supplied in a closed loop form.

The beads are located on the cable by separating them by means of metal spacers. These spacers can be made in the same way as the beads but without the diamond grit embedded therein. The spacers will be of smaller diameter than the beads and may be made of stainless steel or suitable hard plastics or rubber material. At intervals along the length of the diamond wire spacers will be crimped in position.

In an alternative method of locating the beads, the cable with the beads positioned thereon can be coated by injection moulding with a rubber or rubber- like material to retain the beads in position. The moulding will be such that the spacers between the beads are of smaller diameter than the beads and the layer of material over the beads is thin.

A further method of locating the beads is to simply solder them in position.

It will be appreciated that the diamond wire can be made to a diameter much smaller than the smallest conventional diameter of about 6mm. This will enable users to produce products with a greater definition and less wastage of product material.

It will further be appreciated that breakage of a diamond wire made in accordance with this invention enables the majority of the beads to be recovered for re-use on a new cable, Other appreciable advantages of the use of beads as described are that in relation to the cutting diameter a thicker and stronger wire cable can be used giving greater strength, longer life and faster cutting speeds. The use of nickel to electroform the beads results in a bore that is favourably resistant to wear against the wire cable. The diamond wire will also be of lightweight.

All of these advantages lead to savings on costs of production.

It will also be appreciated by one skilled in the art that the diamond grit can be replaced by cubic boron nitride grit, as already mentioned, or other abrasive grit suited to specific application, without departing from the scope of the invention.