BK Tooling's approach to investment, however, has been cautious. For example, some five years ago managing director Robert Tunks started investigating his toolholding options, including hydraulic and shrink-fit systems. He says: "To be honest we liked the concept of shrink-fit tooling but the thought of using heat and the associated risks, combined with the time required to change a tool using heat shrinking and the overall investment in toolholders and equipment were enough for me to say: hold off." He continued to review the various systems on offer until a chance visit to an open house at XYZ Machine Tools brought WNT's Centro-P precision collet chuck system to his attention. This resulted in the purchase recently of a complete package of toolholders for BK Tooling's XYZ 1060 high speed machining centre and bed mills. Mr Tunks continues: "Tool life is important to us and ideally we want a solid carbide ball nose cutter to last for an entire mould, which may be up to seven hours in cut. Therefore accuracy and rigidity in a toolholding system is vital. With Centro-P we get both in a cost-effective package and it does everything we want it to." In one case BK Tooling achieved a fourfold increase in tool life when switching to the Centro-P system. This is attributed to the gripping power of the collet system and also the mass of the holder, which ensures a secure interface with minimal runout of 5 micron when used with WNT's precision collets. A further advantage associated with Centro-P's high grip and rigidity is that it allows smaller toolholders to be used allowing greater access to mould cavities or when working against deep shoulders. "We typically run 6 mm ball nose cutters and before these would have been held in ER32 collet chucks to get the level of rigidity that we needed, says Mr Tunks. "Now, we are using a 16 mm Centro-P collet chuck and this has made a significant difference to where we can access a part to machine it." Centro-P toolholders are balanced to G2.5 at 25,000 rpm as standard to further improve tool life and component surface quality. This accuracy is helped by the design, which involves precision grinding of the 30º trapezoidal threads on the chuck and lock nut to ensure high levels of repeatability and clamping forces that, in addition to being evenly distributed, are 100% higher than in conventional ER collet applications. Clamping and unclamping is achieved by using a specially designed wrench that uses taper roller bearings to grip the smooth collet housing. Additional clamping accuracy can be provided by using the optional torque wrench. Based near Bishops Stortford, Hertfordshire, BK Tooling offers a comprehensive plastic injection mould tools manufacturing service from design through prototype to production tools that can be up to 1 tonne in weight. The tools can be for anything from volume production of low value components through to high tech research and development projects. First published online