Designing tools capable of cutting cleanly and accurately the 15,530 names into the Portland limestone of the Armed Forces Memorial unveiled at Alrewas, Staffordshire, in front of the Queen last month (October) was not straight forward.

As Encore Diamond Ltd had supplied more than 90% of all the diamond tools to Northern Ireland masons S McConnell & Sons for cutting and shaping the Princess Diana Memorial Fountain in Cornish DeLank granite, they thought producing the tools for cutting and shaping the softer Portland limestone of the National Armed Forces Memorial (see last month\'s NSS) would be a piece of cake.

Encore supplied metal bond blades for the initial cutting and shaping of the blocks with excellent results, but the real challenge came with producing Richard Kindersley\'s fine and distinctive design of lettering for the 15,530 names to be cut by one of McConnell\'s big Omag CNC workcentres.

The letters are only 25mm high and required deep, thin strokes, \'V\' cut at 60∫ to a point.

With so many names to be carved within a short timeframe it was imperative that the tools would consistently produce the high level of finish required while lasting long enough to be economical in use.

Encore\'s solution was to design tools in polycrystalline diamond (PCD).

PCD is formed by applying ultra high pressure and high temperature to diamond and metal powders. Its advantages over other diamond tooling include: good finish, accuracy, fast cut, constant performance and the fact that the tools can be re-sharpened.

PCD is a lot more expensive than tungsten carbide and does need to be used with an accurate CNC machine and careful operator, but is cost effective when designed and used properly.

The first tool Encore designed performed well, but the second broke almost immediately, the small, hard pieces of shell in the stone breaking the point off.

Encore tried different hardnesses and made tools of varying malleability. They used a mixture of fine and coarse grained diamond to provide a consistent finish, never altering more than one design feature at a time, until they produced a tool that was ideal for the purpose.

Although it is possible to design a tool with more impact strength and hardness, this has to be linked with operation and accuracy, feeds and speeds.

McConnells understood that the skill of the machine operator was important. If rates of feed or plunge are increased swiftly the tool could crack.

PCD has been used in the stone industry for several years, but this was surely the largest stone engraving contract carried out in the UK using PCD tools.

Barrie Whorrall, the Managing Director of Encore Diamond, says: "I believe the monument will stand for years to come as proof of the achievements of modern technology and the skills of those who master it.