By installing a re-engineered Toyoda GL4A-100 CNC cylindrical grinder, fast-growing sub-contract machinist Emerald Precision was not only able to secure a long-term contract for producing rotors and cylinders for use in air tools, but also consistently maintain tolerances within 5µm on critical bearing diameters.

Emerald director Gerald Balk said: “We have grown by 20% this year, installed additional new machines and increased staff numbers. If we can recruit more skilled people, we expect to see similar rates of growth next year.” He says the Toyoda machine — a production cylindrical that was sourced from an automotive manufacturer by Hinckley-based 2D CNC Machinery Ltd (www.2DCNC.com) and subsequently re-engineered — has contributed to this success.

“Even with the level of re-engineering carried out by 2D CNC’s grinding specialist, it cost a third of the price of an equivalent new machine; it will achieve a great return on the investment.”

He says the fundamental accuracy of the machine is in its original design and build. “The specification includes Hofmann HK5000 water-injected automatic wheel balancing, auto-dressing cycles, gap elimination, Toyoda in-process gauging, coolant with 20µm filtration and mist extraction systems. This results in us having a very high specification machine and this definitely shows in the level of consistency of the work it produces.”

The two rotor and cylinder components previously mentioned are initially pre-turned in a single operation on Citizen CNC sliding-head turn-mill centres, leaving 0.20/0.25mm stock on diameters and 0.15/0.20mm on faces for grinding following case hardening to 60HRC. The rotor component, which is 26mm in diameter x 60mm long, is ground in two operations by inclining the wheelhead at 30deg to create
an angle approach for finish grinding a 9mm-diameter x 12mm-long journal to a tolerance of 5µm. The adjacent face and outside diameter are ground to 25.90/25.875mm over an interrupted surface created by longitudinal slots in the diameter. For the second operation, a probe is used to pick-up the datum setting on the rotor and the second bearing diameter, which also features longitudinal slots.

Meanwhile, the cylinder component, which is some 40mm in diameter x 56mm long and features an eccentric 31mm-diameter bore that is 2.5mm off-centre, is located from its previously honed bore on a face plate and the outside diameter ground to a tolerance of 0.05mm; this diameter also includes interrupted cuts due to grooves and slots. Meanwhile, an adjacent face that has to be geometrically square to the bore and parallel to the opposite face is ground to an overall tolerance of 0.025mm.

The grinding machine’s re-manufacturing process to meet Emerald’s specification included a complete overhaul in which each sub-assembly — such as workhead, ballscrews, tailstock, coolant and filtration systems — was assessed and either repaired or replaced as needed. As the basic machine is built on a heavily ribbed cast bed with semi-hydrostatic ways preventing any metal-to-metal contact in the slideways, wear that could have adversely affected machine performance was non-existent.

The machine has a swing of 320mm, 1,000mm between centres and is controlled via a Toyoda GC32 U1 colour CNC system. The non-swivelling workhead has a variable speed drive (10-500rev/min) and the patented hybrid Toyoda STAT hydrostatic/hydrodynamic bearing system for the wheelhead and ways was totally within its original specification. The wheelhead is powered by a 5.5kW motor that gives a wheel speed of 45m/sec for wheels up to 455 x 75 x 127mm; a wheel width of 100mm is available as an option.

Family-owned Emerald Precision was set up in 1993 by Mr Balk and his wife Alison (who manages the commercial side of the business) with some seven CNC machine tools. Initially, optical equipment and components for scientific instruments were produced; the company also provided a prototype development service for customers.

In fact, it was this prototype development that led Emerald into the automotive aftermarket, for which it provided general machining operations and specialised finishing processes — plus some electronic assembly.

The company employs 12 people, nine on the shopfloor, and took on two apprentices this year (it is currently still recruiting). It spent £180,000 on equipment last year, which included a five-axis vertical machining centre and a CNC horizontal honing machine.