Click on the advert above to visit the company web site

Product category: CNC automatic lathes
News Release from: Star Micronics GB | Subject: Star CNC sliding head automatics
Edited by the Manufacturingtalk Editorial Team on 27 May 2002

Sliding head autos beat ten-year old
Swiss types

Single-hit machining of complex components on sliding-headstock lathes results in phenomenally better mill-turned products compared with 10 year old Swiss-type lathes says a subcontractor.

Single-hit machining of complex components on Star sliding-headstock lathes at subcontractor Small Engineering, Wimborne, results in phenomenally better mill-turned products compared with Swiss-type lathes bought in the early and mid 1990s, according to proprietor, Martin Small In addition, he says that the machines are so reliable that he has had no hesitation in fitting fire extinguishers to his four Star lathes and running them unattended overnight, confident that he will have bins full of good components the next morning

Provided that the setting is spot-on and the tooling and lubricant are of good quality, the last-off component in the morning is usually within two microns of the first-off the previous day.

As with all CNC lathes, especially those with sub-spindle and driven tooling for second-operation work, the Stars are good at producing short runs and even one-offs economically.

"This is an ideal marketing tool for us as often the one-offs are in fact trial parts and there is a larger order ready to follow on; really the customer is just checking out our capabilities" remarks Mr Small.

"What they get from1 us is a true production sample, not a look-alike machined on other equipment, so they are confident that all the parts subsequently delivered will be of exactly the same quality as the prototype." Another observation of Mr Small's is that there is very little a fixed-head lathe can tackle that a sliding-head machine cannot within the diameter range that he is concerned with, I e up to 20mm diameter (Star machines go up to 32mm maximum).

Conversely, conventional lathes could not possibly machine much of what is bread-and-butter to a Swiss-type - the more so at Small Engineering as the company specialises in production of smaller parts.

Average components are 6 to 8mm in diameter and currently the smallest is just 1.5mm.

Consequently there are no fixed-head production lathes on the Wimborne site.

The tenet that sliding-head machines are suitable only for producing slender, shaft-type work has been systematically dispelled over the past few years, and this subcontractor is a prime example of one that has taken full advantage.

While around 65 per cent of throughput is a tradition 'long' part whose length is three times its diameter or more - exceptionally up to 35 times (4mm O, 140mm long) - the remainder is shorter and 15 per cent are larger in diameter than their length.

Mr Small reckons that in the early 1990s the number of BTMA (British Turned parts Manufacturers Association) members using CNC sliding-headstock lathes was about five per cent, whereas anyone checking the current handbook will probably find the proportion is now more like a quarter - and growing.

"These machines are really coming into their own now," he says.

The idea that lathes are just for turning is another idea that is well on its way out.

Some of Small Engineering's customers' parts are milled for around 80 per cent of the machining cycle, allowing standardisation on round bar with recourse to hexagonal or square stock being rare nowadays.

Another strong trend is towards the use of the sub-spindle, he suggests, pointing out that 95 per cent of his components are transferred even if it is just for pip-less part-off, but more usually for true second-opping.

Similarly, driven tool work is carried out on about half of components, a proportion that is also increasing.

There is little surprise in these trends, as all result in more added value to a component and hence more profit for the subcontractor.

As an aside, Martin Small highlights the attention to detail that Star pays to its lathe designs.

With powered tooling being used more and more, manufacturers are looking to push the boundaries of their application.

Mindful of this, Star has equipped its latest machines with four powered rear end-working tools, rather than the usual three provided by other OEMs.

While this may seem trivial, the practicalities are not.

For example, many is the time that components are centred, drilled, tapped and broached on the reverse end at Small Engineering.

Or sometimes a lot of swarf builds up on a particular tool.

By placing it on the end of the gang toolpost and leaving the adjacent position free, the remaining two tools may still be used effectively.

Small Engineering specialises in the production of simple to complex parts for the electronics industry, as well as sectors requiring smaller components such as medical, dentistry, fibre optics and modelling.

Aerospace and offshore are other industries supplied.

The majority of work is in stainless steel, but ranges from free cutting materials up to Nimonic.

"Regardless of the metal being machined, Star lathes have the rigidity to ensure excellent repeatability, geometric accuracy and quiet running," says Mr Small.

"If anything goes awry, the response from Star's UK subsidiary, A and S Precision is rapid irrespective of whether an engineer is calling or advice is being given over the telephone." Established in 1985, the subcontract turning company started with Mr Small gaining an enterprise allowance grant, building his own workshop and buying a centre lathe (which he still has).

He relocated to his current premises in 1988 and took on his first employee, at which time he decided that the future was in supplying high tech industries with smaller, more complex parts.

Increasingly his customers were asking for second operations to be completed, but the problem he encountered was that the smaller the parts are, the more difficult they are to handle and re-fixture for subsequent machining.

In 1993 he bought his first second-hand sliding-head machine, bypassing cam-type equipment and going straight for CNC.

The 10mm capacity lathe allowed a level of precision, repeatability and productivity that was a quantum leap forward.

So he bought another second-hand machine a year later - this time of 16mm capacity.

However, there was no sub-spindle and only one driven tool on these early models, which he describes as "first generation".

Visiting exhibitions in the mid 1990s convinced Mr Small that CNC sliding-head lathes had evolved sufficiently to be called "second generation".

They had a sub-spindle, several live tools, magazine bar feeds; in fact they were purpose-built rather than being CNC-ised cam auto's.

But he still could not afford to buy a new one so continued buying older machines on the second hand market.

1996 saw the installation of two Star VNC20s, the first on site with sub spindle and driven tooling.

Parts started coming off complete, providing another step forward in productivity.

Even these older machines from Star are well built, suggests Mr Small.

Certainly the rigidity, accuracy and reliability were evident and the machines appeared to be well built.

Proof of this came from an unlikely source.

Mr Small knocked the turret of one VNC20 out of alignment and, as he did not employ a maintenance engineer at the time, he asked a local engineer to repair the machine.

Unprompted, he commented that the parts of the machine you see when it is stripped down are of equally good quality to the parts that you normally look at.

Satisfied with this independent advice, in 1999 Mr Small embarked on a programme of buying new Star lathes with the installation of an SA-12/16.

A second was acquired a year later; and then one of the VNCs was part exchanged for a new SR-20R.

These are "third generation" machines in Mr Small's parlance, capable of cycle times as fast as one third of those possible on the VNCs.

One SR-20R machining example cited is the production of an unusual offshore valve component in 316 marine-grade stainless steel.

It is 8mm diameter but just 1.03mm long so there is little material to grip on after part-off while second operations are performed.

The customer previously made these parts on a fixed-head lathe followed by a sequence of manual operations and then auto lapping, starting with 700 pre-machined components to end up with 500 good ones several weeks later.

Now they are produced complete in a two minute cycle on the SR-20R, as follows.

Left hand spindle: Op 1: centre and drill a 2mm diameter through-hole in the bar end.

Op2: form tool plunges a 0.4mm radius semi-circular groove around the periphery.

Op 3: Carbide slitting saw produces 1mm wide slot across the face to a depth of 0.4mm.

Op 4: Replunge groove to deburr after slotting.

Op 5: Turn face to deburr; turn diameter; back chamfer.

Right hand (sub) spindle: Op 4: Eject finished part onto conveyor.

Op 1: The same saw produces a similar slot in the reverse face, but at 90 degrees to the first slot.

Op 2: Re-drill bore to remove burrs.

Op 3.

Turn back face again to remove burrs from rear slot.

Particularly innovative is the use in the sub-spindle of a collet with an extended-nose and a cut-out to accommodate the circular saw to achieve sufficient slot depth in the component.

Very precise positioning of the machine slides is needed in this application, as the collet is effectively 'rubbing' against the tooling.

A and S provided assistance to optimise this job, which has a drawing tolerance on face parallelism of 0.025mm.

In practice, 0.010mm is achieved.

It is these sort of results that prompt Mr Small to use the word "phenomenal", particularly in this case as the component is being clamped over a very short length.

The cycle time will be reduced further as repeat orders for batches of 500-off are regularly received.

Moreover, enhancements to the operations will probably allow the final ceramic vibratory deburr operation to be eliminated.

Set-up of the SR-20R for producing this component is just 2.5 hours, so effectively this is the lead time for the job as the customer can take delivery of first-off components almost immediately if required.

Mr Small points out that successfully completing this demanding job has resulted in further work from the same customer.

Small Engineering has continued to expand its customer base, even over the recent difficult trading period, as every part can be produced in a single hit.

There is now virtually no second operation work carried out manually at the Wimborne works, either by machine or by hand.

(This was Manufacturingtalk's Top Story on 24 May 2002).

• Star Micronics GB: contact details and other news
• Email this article to a colleague
• Register for the free Manufacturingtalk email newsletter
• Manufacturingtalk Home Page

Search the Pro-Talk network of sites

Put your news on Manufacturingtalk  |   Advertise  |   Get the free Manufacturingtalk newsletter  |   Manufacturingtalk Home
About Manufacturingtalk  |   Copyright © 2000-2008 Pro-Talk Ltd, UK