To grind blades, such as razor blades and scalpel blades, the blade is placed at the cusp between two abrasive wheels which have spiral grinding surfaces which are meshed with each other.

Prior art grinding wheels have been manufactured by electroplating the whole of the outer periphery of a wheel with a grinding medium, and then forming a spiral groove in the plated outer periphery by spark erosion.

The remaining spiral land of a wheel, which is still coated with the grinding medium, can then engage with the groove of a complementary wheel. This results in considerable waste of the grinding medium since more than half must be eroded away to provide interlocking spirals. Also, the use of spark erosion limits the depth of the groove which can be cut, and hence the thickness of the available grinding medium.

The present invention provides an abrasive wheel having an abrasive surface extending in a spiral around the outer periphery of the wheel, a spiral groove being defined between the turns of the abrasive surface to allow meshing of the abrasive surface with the abrasive surface of a like wheel, wherein the abrasive surface of the wheel is formed by attaching together a plurality of abrasive surface sections which extend in the spiral direction around the outer periphery of the wheel.

A greater depth of cutting medium can be used, whilst manufacturing costs can be reduced.

Very preferably each section extends for approximately a complete turn, 360 degrees, around the outer periphery of the wheel. Preferably a section forms a pitch of the spiral.

Preferably the abrasive surface sections are separated by sections of smaller radial dimension, to form a recess between adjacent abrasive surface sections in the axial direction. Preferably, the abrasive surface sections and the spacer sections are mounted on a cylindrical hub.

Preferably the hub has a radially extending flange at one end, with a spiral radial face against which the sections bear.

Preferably the sections are joined in the axial direction by pins or bolts extending through the adjacent sections.

Other preferred features and advantages of the invention will be apparent from the following description and the accompanying claims.

The invention will be further described by way of example, with reference to the accompanying drawings, in which: Figure 1 is an isometric view of a grinding wheel forming an embodiment of the invention; Figure 2 is a cross-section through a diameter of the wheel of Figure 1 in the direction of arrows D; and Figure 3 is an exploded view of the wheel of Figure 1 on a reduced scale.

Referring to Figure 1, a grinding abrasive wheel 1 in accordance with the invention comprises a central hub 2 having a boss 4 which is mounted on a drive shaft (not shown) for rotating the wheel, and an outer rim 6. The outer rim 6 has a radially extending flange 8 (see Figure 2) against which grinding material sections 10, spacer sections 12 and an end section 14 are secured, as will be described more fully hereinafter.

Referring to Figure 3, a grinding material section 10 comprises a split ring 16 of bronze having a layer 18 of grinding material bonded to its outer peripheral edge. The grinding medium is bonded to the outer periphery of the bronze ring in a sintering process, and the ring is then cut radially. The thickness of the grinding material in the axial direction of the wheel 1 is slightly greater than the thickness of the ring 16. Holes 20 are provided in the ring 16 for receiving mounting bolts 22, one of which is shown in Figure 3.

Spacer sections 12 are also formed by a bronze split ring, having mounting holes 23. The spacer sections 12 have a thickness in the axial direction which is sufficiently great so that the space between adjacent turns of the grinding material 18 (see figure 1) is greater than the thickness of the grinding material in the axial direction. This enables the spiral grinding surface 19 (shown shaded in black in Figure 1) formed by the sections 10 to mesh with the spiral grinding surface of a complementary wheel.

As seen in Figure 3, the flange 8 on the hub 2 has a spiral radial inner surface 24 against which a first grinding section 10 will sit, fitting snugly about the outer rim 6. The pitch of the spiral surface 24 is equal to the combined thickness of the first grinding and spacer sections 16,12.

To assemble the grinding wheel 1, three grinding sections 10, interleaved by two spacer sections 12, are slid onto the rim 6. The sections adopt a spiral profile dictated by the spiral surface 24 on the flange 8. The use of bronze allows the rings to conform easily to the spiral profile of the surface 24. Other materials may be used for the rings 10,12. The end section 14, which has a complementary spiral radial surface 24, is then slid onto the rim 6. The end section 14 has threaded holes 26 to receive bolts 22 for tightening the sections 10,12,14 against the flange 8.

It can be seen that the outer periphery of the wheel in the region of the grinding surface 19 is formed by removable sections, in this case by grinding section 10 and spacer sections 12.

Once assembled, the grinding surface 19 of the wheel 1 can be dressed to remove any radial unevenness, particularly at the join between the grinding sections 18. In use, the bolts 22 serve to secure the sections 10, 12 against radial as well as axial movement, and by providing an adequate number of bolts, in the example eight, there is little risk of sections breaking away.

It will be appreciated that wheels of greater axial length can be built, simply by increasing the number of grinding and spacer sections 10,12.

Also the sections 10,12 need not each extend 360 degrees around the rim, for example 180 degrees might be preferred, however 360 degrees is preferred for simplicity of assembly.

For grinding the cutting edge of small blades such as scalpel blades, a wheel of about 200 mm outer diameter at the grinding surface 19, and overall axial length 50 mm, the grinding surface extending for about 30 mm with a pitch of about 8 mm is suitable.

The grinding wheel has utility in other manufacturing processes, for example for grinding an edge on a knife blade. Also, it will be appreciated that the term grinding can also comprehend other processes using an abrasive material, for example"finishing"or"polishing", the process depending on the nature of the abrasive medium, rather than the structure of the wheel.