By P. A. PARAMESWARAN

Using the correct tool is very important for achieving high productivity with consistent quality. What are the important factors to be considered and followed to select the right tool for the processing requirements to obtain a good edge life, cutting quality and thereby achieve a lower tooling cost?

The tooling specifications given in the machine manual need to be carefully studied and the tool selected accordingly. In most cases one set of tools would have come with the machine, which can also be used as an additional confirmation of the specifications.

This ensures that the maximum tool diameter or the collision length is not exceeded. The bore or shank of the tool should be such that it fits correctly without any slippages on the machine spindle or in the collet of the clamping chuck. Following are some examples of tool selection based on the machine:

Sawblades: These should never exceed the maximum diameter given in the machine manual. The kerf of the sawblade (the cutting width) is as per the thickness of the material being machined – thicker the material more the kerf and vice versa.

On panel saws or beam saws care must be taken to match the kerf of the main sawblade and the scoring sawblade to achieve chip-free results. When using thin kerf sawblades for minimising material wastage, never exceed the recommended material thickness. This will prevent the sawblade from developing a bend or a crack.

Bore tools: When selecting a tool, especially with large profile depth, care must be taken that the tool diameter does not exceed the maximum tool diameter possible on the machine, so that it does not foul with the fence or metal parts on the machine.

On multi-spindle machines always check the direction of rotation of the spindle and select the tool rotation accordingly. The length of the drill bit should not exceed the collision length given in the machine manual.

On multi-boring machines each diameter of the drill being used must have both LH (orange or red colour) and RH (black colour) options.

Router cutters: The diameter, length and shank diameter of the tool should be suitable for working on portable or pin routers with manual feed, or on CNC machining centres.

The clamping systems (HSK, ISO, etc.) and the respective collets are to be selected as per the specifications given by machine manufacturer. Also to be taken into consideration is the type of feed on the machine:

•        Is the material being manually fed by the operator? Or

•        Is it by mechanical/ automatic feed? Or

•        Is it a CNC machine in which the material is clamped with the tool being programmed to move?

On manual feed machines always use tools with limitors for ease of feed and operator safety. For mechanical automatic feed machines and CNC machines attention must be paid to:

•        The tool should be stable and capable of running at the feed rates being maintained on the machine

•        The feed rate is selected according to the number of cutting edges on the tool

•        The RPM is selected as per the tool diameter

•        Never run a tool faster than the specified parameters – operator safety will be compromised

•        Never run a tool capable of high feed rates at a slower feed rate. If a Z4 tool capable of higher feed rates when run at a lower feed rate of a Z2 tool will end up damaging the cutting tips of the tool as well as making burn marks on the workpiece due to the friction.

•        Feed rates for the different tool categories are normally given in graphs in the catalogues. Always refer the graph of the tool being used and set the RPM and feed rate accordingly.

Of material

The life of a tool depends on using the most suitable cutting edge and the correct configuration of the cutting edge for the material to be machined. The best example to illustrate this aspect is in the case of the basic cutting or sizing process using sawblades.

When machining solid wood a flat tooth configuration (for cutting along the grain) or alternate bevel tooth configuration (for both along and across the grain) is what is normally used.

But it is also required to check if the wood is seasoned and the moisture content is within 15%. If the moisture content is above 15%, sawblades with wiper teeth are to be used.

When machining boards laminated with HPL it can be seen that the life of the sawblade drops by 50% to 75% (depending on the thickness of the HPL overlay and the backing laminate) as compared to the life of the same sawblade when sizing pre-laminated boards with thin paper or melamine laminate.

To increase the tool life, it is required to replace the flat trapezoidal tooth configuration with a fully trapezoidal tooth configuration.

In general tungsten carbide cutting material that is available in different grades gives good results on wood and wood derived materials. But certain high-density materials like compact laminate can be machined only with polycrystalline diamond (PCD) tools.

Since the average life of a PCD tool is around 25 times more than that of a TCT tool, it is also used in larger factories to minimise the machine downtime due to frequent stoppages for tool change and to reduce the tooling inventory.

To summarise, a high-quality machine without high quality tooling will be like a racing car on wooden wheels!

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