North Somerset Reproductions (NSR), Bristol, Has purchased its first CNC automatic lathes to stay competitive
Established in Bristol in 1963, North Somerset Reproductions (NSR) has always specialised in subcontract manufacture of precision turned parts up to 20 mm diameter on sliding-head lathes. John Duerden, a partner in the family-owned company which operates 20 cam-type auto's, has recently bought his first two CNC machines - Star lathes from A and S Precision Machine Tools - and has seen startling benefits for his company. 'It is vital that firms like ours invest in CNC technology just to stay in business let alone remain competitive,' says John.

'If they don't, they won't be here in 10 years time.

'You can see the way things are going from the second hand market.

Three or four years ago we used to get œ3,000 when we sold an old cam machine.

Now you are lucky to get œ1,000 for one - hardly anybody wants them.' In March 1999, John took the plunge and cleared out four cam auto's from his machine shop.

He needed to borrow only half of the œ80,000 purchase price of a Star SA-12 and he made sure that he had the right type of value-added work waiting to be put on the lathe as soon as it was installed.

Within a couple of days the machine was working round the clock, seven days a week and it paid for itself within 18 months.

John says that the output from the SA-12 is equivalent to three to four cam-type machines.

Moreover the labour cost element is much lower with the CNC lathe.

As he lives near to the Small Street works in the St Phillips area of Bristol, he is able to go in at midnight and stock the full length FMB bar magazine with sufficient material to last through until 6.00 am when the first day shift starts.

So he benefits from six hours unattended running every day; and during the other shifts, operator attendance is minimal.

It was not only productivity that improved with the introduction of the Star lathe.

Scrap was reduced and so too were noise levels, the latter thanks mainly to the quiet running of the FMB magazine.

Machine shop manager, Stefan Lamch, comments that accuracy has also improved.

He says, 'The Star SA-12, and the SR-20R which we bought a year later, easily hold 10 microns total tolerance on diameter which is three times better than our cam auto's, especially if we are machining steel.' He goes on to explain that the Stars are ruggedly built.

Before the 20 mm capacity SR-20R was installed, NSR wanted to use the SA-12 to machine components larger than its 12 mm capacity.

So they opened it up to do just that, with excellent results, even though some parts were stainless steel and cycles included heavy milling and drilling.

'You need a strong machine to be able to do that,' comments Stefan, 'as you do to be able to broach, which is no problem on the Stars and virtually impossible on our conventional sliding-head lathes because they are not rigid enough.' Referring again to the precision with which components can be machined, Stefan cites a bronze part which needed a 0.3 mm diameter hole drilled in one end and whose tapered OD had to be turned down to 1.8 mm diameter from 12 mm bar, as this was the only size available.

NSR would never have attempted this on a cam auto.

One hit machining is the watchword for all multi-axis CNC lathes with full opposed sub-spindle and driven tooling, whether they have a fixed or sliding headstock.

The SA-12 and SR-20R at NSR are prime examples of the benefits which may be derived from using such versatile lathes to complete-machine even the most complex parts.

John Duerden says that a quarter of the parts he previously turned on his cam auto's required second and even third operations on other machines.

All these components are now produced complete on the Stars in one set-up, including driven tool work and reverse-end machining.

New business is just as important as keeping existing customers happy.

So it is with considerable satisfaction that John points out only 30 per cent of the work carried out by the Stars has come off the cam machines - the remainder is new work which has been won as a result of having the enhanced sliding-head turning capacity.

Everything from PTFE to stainless steel is machined in batches of 50 up to 10,000-off.

Cycles of 5 minutes are exceptional, with the majority closer to the minimum of 10 seconds.

Speed of changeover is therefore important to NSR in order to minimise non-productive time.

Here again, CNC machines score heavily over conventional cam-type auto's, as the former take just four to six hours to reset for a completely new job whereas the latter take typically two days including changing, pulleys, belts, gears and cams.

Repeat jobs are also much quicker into production on the Stars, sometimes taking as little as 15 minutes if the same bar and tooling are used and it is only necessary to download the program.

Anyone who is daunted by the idea of computer-controlled turning can take heart from Stefan Lamch who, without any previous CNC experience, picked up programming off-line and editing at the machines after only three days' training by A and S Precision.

As for NSR, the seven-man subcontractor is set to carry on growing on the back of continued investment in Star CNC lathes, and at the expense of most of its cam automatics.