focus www.btma.org
Sliding-head lathes are as fast as ‘multis’; and cycle times are reduced by a third using form tools.
Competitive advantage
THE two Star CNC sliding-headstock lathes operated by
Reading-based Rodmatic can mill-turn components of medium to high
complexity as quickly as any of the 42 cam-type, six-spindle automatics
on site, according to owner and managing director, Brian Steatham.
He also points out that the turned finish achieved using the Stars,
mainly on stainless steel and steel components, is so good that
subsequent grinding is frequently eliminated, lowering unit
production cost significantly.
A multi-spindle auto takes around two days to reset, so batch sizes
above 30,000-off are needed to justify the time investment. By contrast,
sliding-head lathes can be set in a couple of hours, so much smaller
runs are economic. Rodmatic has produced batches as low as 7-off on
the Stars, although runs can be up to 5,000-off. In this connection,
Steatham has the following tip for precision turned parts
manufacturers: ‘When producing larger batches on CNC sliding-head
lathes, think of using form tools alongside single-point cutting tools to
reduce cycle times.’ Rodmatic often does just that, using its experience
of wire-eroding and grinding form tools for the multis and
transferring the technology to the sliding-head machines. Dramatic
reductions in cycle times are achieved, typically of around 30%.
One component regularly produced, a profile-turned and bored
steel shaft for a European customer in the fluid power sector, is
machined in part by form tools in an overall cycle of 37 seconds. This is
over 38%faster than the 60 seconds it used to take by exclusively singlepoint
cutting. The competitive advantage this gives Rodmatic has
resulted in considerable business success at a time when many
subcontractors are struggling. Whereas order intake for the multis was
down by 20%during the last quarter of 2008, the sliding-head lathes
continued to work flat out during that period, 24 hours a day.
Since 2006, when Steatham formed the company’s CNC division,
Rodmatic Hytek, he has invested £1.5 million in new plant for turning,
prismatic machining, wire erosion, tool grinding and component
washing. He plans to continue investing at the rate of three to four
CNC machines per year, the latest having been installed at the end of
January 2009. £1.5 million of new orders received from two UK
companies since the beginning of 2009, spread across multi and CNC
work, gives credibility to Rodmatic’s investment plans. Around half of
turnover currently comes from European companies, mainly in
Germany, and this proportion is likely to increase, helped by the
continuing strength of the Euro against Sterling. Another area of
recent success has been in the UK autosport sector, with three new
customers won in 2008.
Many of the new components are being put onto the Star slidinghead
lathes, which are also regularly taking work from the multis as
batch sizes fall. Tolerances of ± 2.5 microns are routinely held on the
sliding-head machines, which would be very difficult to achieve on the
multis. Equipped with a four-metre bar magazine and high-pressure
coolant to allow long periods of unattended running, the first Star was
a 9-axis SV-32 of 32 mm bar capacity, installed mid 2007. It was
followed in 2008 by a similarly equipped, 7-axis SR-20RIII for millturning
parts up to 20 mm diameter. They joined three multi-axis CNC
fixed-head lathes for producing larger components.
When asked why he did not continue down the route of fixed-head
lathes to satisfy the market’s increasing demand for smaller size, high
accuracy mill-turned parts in lower volumes, Steatham says that in his
opinion, a sliding-head lathe is twice as fast as an ‘equivalent’ fixed-head
lathe, ie one with a counter spindle and two turrets containing driven
tooling. ‘Major factors slowing fixed-head lathes are their inability to
cut with more than two tools simultaneously, and long turret indexing
times compared with the rapid infeed of gang and crossworking tools
on sliding-head machines,’ he suggests. He also likes the advanced millturning
and simultaneous end-working capabilities of modern slidingheadstock
lathes, as well as their traditional strength - that of producing
shaft components accurately due to the support given by the guide bush
at the point of cutting. During machining trials against competitive
sliding-head lathes, the Star machines were inherently faster. In
addition, Brian Steatham feels that their extra weight and rigidity allow
the production of more accurate components.
In a prediction that will encourage all involved with manufacturing
in the UK, he thinks that it will start to emerge from recession before
the end of 2009, ahead of the rest of the economy. Moreover, he
believes that manufacturing has a brighter future now that the country
is in need of value-added industries to replace the wealth formerly
created by the banks. ‘The Pound has been artificially high against the
Euro for a long time due to the apparent strength of the financial
sector in the UK, but that is no longer the case. In fact it wasn’t for most
of 2008, which is why we and many other UK-based suppliers have
been winning business from Continental Europe and I expect the trend
to continue. We are still seeing a lot of interest from the Eurozone.’
www.stargb.net www.rodmatic.co.uk
88 MWP march 2009
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