Where standard CNC lathe is the best choice

In some types of small batch work, component geometry and non-turning content determines that a standard CNC lathe is more suitable than a mill-turn centre says an antennas manufacturer.
Stratford-upon-Avon based Precision Antennas is experiencing a boom! Since the start of 2002 the company has expanded its workforce by almost half to 192 people and is adding to its factory capacity. In line with this expansion, the company has recently installed two of the latest Colchester Tornado 220 lathes, bringing the number of Tornado machines in the factory to four. Precision Antennas is privately owned with over 50 years' experience in the development and manufacture of antennas and associated support structures.

Its installed manufacturing capabilities support the fabrication of dish-form antennae up to 6.4 metres in diameter, and single piece and hand-spun antennae up to 4.5 metres.

Manufacturing manager, Alan Brooks explains the philosophy that has created such success: 'Our ability to design, develop and build virtually all our key components in-house not only guarantees quality and performance but it also means we can respond very quickly to customer's needs.

Our customer base is largely drawn from the mobile telephone industry, OEM radio systems manufacturers, global communications service providers and the defence sector.' The company's products are exported worldwide, either directly and indirectly, and due to the nature of the business, almost all manufacturing output is made to contract.

While batches can sometimes reach 250, quantities tend to be nearer 10 or 20 parts.

Machining facilities at the factory now range right up to full five-axis milling capability.

For two-axis turning, the company has focused on chucking versions of the Colchester Tornado which originated with the installation of a Tornado 100, followed by a larger capacity 210 machine.

Precision Antennas was then one of the first companies in the UK to install the latest Tornado 220 following its launch in 2001 and quickly followed with a second machine as production demands grew.

As Brooks maintains: 'When you look at the value for money aspect of the Colchester product we don't know of any other lathe on the market that can match it.' He follows on to outline that although some of the turned parts require subsequent drilling and milling operations, because the batch quantities are so small, breaking the turning from machining of the other features is the most cost-effective method and a Tornado is quicker to set up than a mill/turn lathe.

Brooks describes how the Tornado machines can maintain tolerances without any problems and the operators and setters particularly like the improved ergonomics and working area of the latest 220 compared to the 210.

He describes how having four machines out of the same stable means operators can easily move from machine to machine without thinking, and the company has excellent backward/forward capability with CNC programs giving considerable tooling flexibility.

'When you bear in mind the Tornado 220 was some 20 per cent less expensive than the previous 210 model, it is certainly a lot of lathe for the money.

An additional factor in the decision to stay with the Colchester product is the good after-sales support we have received.' The original Tornado 100 has a bar puller which enables bar lengths to be machined, but by far and away most operations across the four machines are based on castings and sawn billets.

Component diameters span 25mm to 350mm and cycle times vary between 90 seconds and 15 minutes.

'Operations mainly comprise outside turning, face grooving, boring and internal tapers and grooves but we also machine quite a lot of parabolic curves which require interpolation,' he says.

Coupled with program delivery by DNC, most changeovers take around 30 minutes which includes chuck jaws.

But as Alan Brooks describes, the improved ergonomics of the latest 220 machines make life much easier.

Among the improvements in the machines between the 210 and 220 is the Colchester patented base redesign which introduced 'Duo-stable' construction incorporating an engineered concrete polymer base fill.

To this foundation Colchester added heavier and larger ways which contribute to improved static and dynamic stiffness, and the whole machine has higher thermal stability.

These basic improvements enabled higher power 22kW motors and drives to be included in the specification with much improved spindle design, faster axis motions and turret indexing.

And, with redesign and positioning of the hydraulic tank at the front of the machine and coolant tank at the opposite end, maintenance and swarf removal is easier and operational benefits through grease lubrication in favour of total loss oil, gives improved coolant consistency and cutting tool and coolant life.

The versatility of the machines is further enhanced by the way in which Precision Antennas operates them.

Some components are programmed with stops in the cycle which allow the operator to turn or relocate the part in the chuck jaws before re-starting the cycle.

In addition as three of the machines are arranged in a 'U' formation this enables more flexible operation as a cell.

'The aim is to always get a finished turned component from the machine with one operator visit, and failing that, to progress work through the turning section as quickly as possible,' concludes Brooks.