In recent years there has been a rapid acceleration in the use of polycrystalline diamond (PCD) tooling for cutting wood – from circular sawblades and simple straight-edge cutters to complex profile cutters.

Among the benefits offered are extended cutting life – which reduces tooling costs and minimises downtime on long runs as a result of less frequent toolchanging; a superior and consistent quality finish to the workpiece from the sharp cutting edge; and the ability to cut difficult and abrasive materials at higher speeds than is possible with conventional tooling.

PCD is manufactured by sintering together graded and selected micron-size particles (1 micron=0.001mm) of diamond under conditions of high temperature (approximately 1,400°C) and pressure (approximately 6,000MPa). This is done in the presence of a solvent/catalyst metal, usually cobalt, which remains in the PCD occupying the space between the diamond particles and makes the PCD electrically conductive.

This synthesis process produces a layer of PCD approximately 0.5-0.7mm thick, bonded to a thicker substrate of tungsten carbide, to produce a flat disc or ‘raw blank’ of up to 74mm diameter. This disc is cut into smaller pieces in the shape of rectangles, triangles and semi-circles, which are brazed onto the cutting edges of the tool – the teeth of a sawblade, the tip of a drill bit or the edge of a cutter knife.

Sharp cutting edge

The tool is then machined to bring all the PCD segments within the correct cutting circle and to produce a clean, sharp cutting edge – and in the case of profile tools to shape the PCD to the desired profile.

PCD is as hard and wear-resistant as natural diamond but, in addition, it has better mechanical strength or toughness. This makes it an ideal material for cutting abrasive products such as particleboard, MDF, laminated boards and certain species of solid timber.

PCD tooling has long been used in the automotive and other engineering sectors for a wide range of machining processes on non-ferrous metals and non-metallic materials.

However, until the early 1980s its use was virtually unknown in the woodworking industry. The initial stumbling block was the high price compared with widely used tungsten carbide tipped (TCT) tooling; coupled with the fact that, unlike most metalworking tools which have a single cutting edge, many woodworking tools such as sawblades and profile routers require relatively large amounts of PCD and are more difficult and expensive to manufacture. The size of the ‘raw blanks’ produced then was also smaller than today, which limited their application for woodworking tooling.

Another problem was the technology available to sharpen the tools. The majority of metalworking tools – whether used for turning, boring or milling – are sharpened by grinding with diamond grinding wheels. However, only tools with straight cutting edges and simple male radii can be ground effectively.

The expansion of PCD tooling into areas other than metalworking therefore depended on two key factors: firstly, the development of larger ‘raw blanks’ by manufacturers such as De Beers Industrial Diamonds (Debid); and secondly, the development of technology for producing and sharpening complex form tools.

Debid has played a leading role in expanding the use of PCD tools in the woodworking sector, with an extensive research and development programme that includes working closely with tooling manufacturers and service companies as well as universities on the design and application of PCD tools for cutting wood.

The company’s product for the woodworking industry is marketed as SYNDITE, and is produced in a variety of shapes and sizes from discs up to 74mm diameter, and in several different grades based on the average diamond particle size in the PCD layer. This includes a unique grade specially formulated for woodworking requirements. SYNDITE combines the hardness, abrasion resistance and thermal conductivity of diamond with the toughness of the tungsten carbide substrate. The carbide layer allows the insert to be easily brazed onto the cutting tool body.

In general, the finer the diamond particle size the better the cutting edge and/or surface finish produced; and the coarser the diamond particle size the greater the wear resistance.

For woodworking the most commonly used grades are SYNDITE CTB010, which has a nominal 10 micron grain size and is a highly abrasion-resistant ‘general purpose’ grade often used on small rotary tools such as router cutters; and CTC002 – a nominal 2 micron grain size, chip-resistant material specially developed for circular sawblades.

The second key development required for wide use of PCD tooling in the woodworking sector was technology for shaping and sharpening complex profile cutters. The technique used is electrical discharge machining (EDM), using either a wire electrode or a rotating wheel electrode (the latter known as electrical discharge grinding). EDM is used as a production process in engineering, but for manufacturing and sharpening cutting tools, new control systems had to be developed.

Vollmer, which is the world’s largest manufacturer of equipment for sharpening conventional bandsaw blades and circular sawblades, has used its considerable experience in this field to develop the ‘Q’ family of erosion machines for both circular sawblades and complex cutters.

Electrical discharge grinding has nothing to do with conventional grinding, which depends on the abrasive action of the grinding wheel against the workpiece and involves high grinding forces. EDG is a non-contact process, which means it can be used for thin, fragile shapes.

The process involves generating a powerful electrical spark which discharges between the electrode and the PCD tool, which are flooded with dielectric fluid. This high-energy spark vaporises the PCD under controlled conditions, and it works because the cobalt content of the PCD is electrically conductive (whereas diamond is not).

The PCD inserts are usually rectangles or semi-circles and only a small proportion of this – essentially the edge – is employed in actually cutting. However, as this edge wears, the remaining bulk of the PCD allows the cutting edge to be ground back, or re-sharpened, several times during the lifetime of the tool.

With the availability of suitable size blanks and the technology to machine it into complex tool forms, the use of PCD for cutting wood has been growing since the mid-80s and accelerating more rapidly in recent years. In fact, woodworking is currently one of the fastest-growing markets for PCD tools, according to Debid.

Fuelling demand

Increasing use of abrasive wood based panels, coupled with developments in CNC machinery and automated manufacture – plus the need to improve productivity and quality – have helped fuel demand for high performance, long-life cutting tools in order to reduce tooling costs, minimise downtime for toolchanging and maintain the quality of cut.

Cost remains a significant consideration and is an obstacle that needs to be addressed if more woodworking companies are to be encouraged to switch to PCD tooling. Having said that, prices have fallen significantly – due to competition as the number of manufacturers increased, higher volumes of sales, and more efficient production with advanced CNC erosion machines. A 48-tooth circular sawblade that cost £2,800 around 1986 would now sell for about £940.

That might still look expensive, but woodworking companies need to consider the investment in terms of overall benefits. A PCD tool might cost 15-20 times more than a TCT equivalent, but it will last up to 100 times longer.

Of course, it is important that woodworking companies adopt good in-house tool management procedures. PCD tools should be stored, handled and used properly. If they’re dropped on the concrete floor or slung in a box with a load of other metal tools – or if the workpiece contains contaminants such as stone chips or metal – then the damage could be expensive.

Treat PCD tools correctly and they will deliver the benefits that a growing number of woodworking companies are already enjoying.