Comments like “marvellous value” and “all jobbing shop machines should be built this way” make it clear that Andrew Russell and Stephen Boocock, owners of contract machinists Progress NC, are very keen on their first 5-axis machining centre. It is a German-built Spinner U5-620, the first in the UK, supplied in January 2013 by recently appointed sales and service agent, Whitehouse Machine Tools.
The configuration of the 12,000 rpm, vertical spindle machine places all the linear slideways above the working area. Rotary axes are provided by a 360-degree, 650 mm diameter table mounted on a -90 / +110 degree swivelling trunnion. Unusually, this axis runs from front to back, rather than adopting the more typical side to side arrangement. The non-driven side of the trunnion is supported at the front of the machine by a counter bearing to allow heavy milling and to promote accuracy.
The design allows a footprint of 2,600 mm x 2,350 mm, which is small for a machine capable of milling and drilling a half-tonne workpiece in a nominal half-metre-cube working volume. (Linear travels are actually 620 x 520 x 460 mm.) If Progress NC had installed a traditional design of 5-axis machine of equivalent capacity, the subcontractor would have had to uninstall one of its other machines, as space in the Preston facility is limited.
What also sets the Spinner machine apart from other 5-axis vertical machining centres, in the estimation of Messrs Russell and Boocock, is the comprehensive standard specification. The price is consequently many tens of thousands of pounds lower than similarly equipped 40-taper machines on the market. Hydraulic clamping, glass scales, a swarf conveyor, a 32-pocket tool magazine and a high-pressure coolant pump are all included. Control is by the Heidenhain TNC 620 contouring CNC system.
Andrew Russell commented, “The Spinner specification far outweighed that of other 5-axis machines we considered. It was cutting metal on the first job within 48 hours of commissioning. “You normally expect a few teething troubles when a new machine is installed, but not a single thing has gone wrong with the Spinner.
“We are holding very tight tolerances due to the glass scales, which inherently allow better accuracy and repeatability than the other machines we looked at, which were fitted with rotary encoders.
Stephen Boocock added, “Spinner machines are not that well known in the UK. I had not heard of them before Whitehouse took over the agency, after which I saw the spec of a larger 5-axis machine on their web site.
“Andrew and I went over to see the Spinner factory, where the machine tool builder uses its own lathes and machining centres to make many of the constituent parts. We were very impressed with the rigidity and stability of construction.
“The owner, Axel Spinner, took time out to meet us. We were accompanied to a nearby job shop that uses a U5-620 5-axis machine and we could see how it well it would fit into our operation.”
Progress NC is an archetypal jobbing shop, producing parts for aircraft, boats, guns, motorsport and a wide variety of other industries, batch size ranging from one- to 100-off.
In 1998, when the joint owners resigned from another subcontract firm to establish their own company, they had one 3-axis machining centre and no work. Today, it operates a selection of manual and CNC turning and milling centres as well as spark erosion equipment. A mould / die making service is offered, and reverse engineering is carried out using the company’s co-ordinate measuring inspection facility. The order book for conventional capacity is buoyant and the company is now looking to fill the 5-axis machine’s time.
An early job put onto the U5-620 was an aluminium part for the top of a mast on a £30 million, ocean-going yacht competing in this year’s round-the-world race. The part required all five axes to be interpolated simultaneously to generate complex surfaces, which were programmed quickly from the customer’s CAD model in 5-axis software added to Progress NC’s existing OneCNC CADCAM system.
Other jobs require repositioning the component in one or two rotary axes, which are clamped while machining is completed using the three linear axes. One example was a half-metre long steel tow bar for a commercial vehicle that would have been, according to Mr Russell, a ‘nightmare’ to produce on one of the firm’s 3-axis machines.
Another 3+2 machining contract involved production of a 316 stainless steel injector flange for a diesel truck. The part was produced in two operations on the Spinner, whereas it would have needed five operations on a 3-axis vertical machining centre. The time saving was significant, as a batch of 20-off was required. Moreover, fewer fixtures were needed, reducing workholding costs.
Utilisation of machining strategies involving rotary axis positioning was the principal reason for the subcontractor opting to move into 5-axis machining, i.e. to manufacture 5-sided work more cost effectively. However, preparing cycles offline that interpolate all five axes simultaneously was easy to learn, according to Mr Boocock, who described the company’s entry into the technology as being quick and straightforward.
As a postscript, both partners commented on the rigidity of the Spinner U5-620. Where other machines can sound hollow when a tool is engaging the workpiece, the Spinner is audibly more solid in cut. It is already apparent that tool and insert longevity at Progress NC is increasing due to lower vibration. Consumable costs are saved and the frequency of tool changes is reduced, leading to higher productivity.