Advanced sliding head auto converts subby to OEM

Advanced CNC sliding head automatic lathe with two Y-axis cross feeds each to the turret and toolslide allowed a subcontractor to machine parts for its first original product.

John Harrison, the managing director of Microform Precision Engineering of Clayton West, just outside Huddersfield, UK, has achieved the goal of many subcontract (subby) machinists, that of successfully developing his own product.

Having purchased a Citizen C16 CNC sliding head auto in mid-2004 from NC Engineering of Watford, UK, he then decided three months later that a top of the range Series 3 Citizen M32 -V with two Y-axis cross feeds each to the turret and toolslide was what he needed to produce components for his patented electronic contact probe and tool touch sensor, as well as growing his business in production machining.

Microform Precision was originally set up by Harrison and his wife in 1977.

It bought its first CNC machine in 1989 and 10 years later moved into the current premises when they were first built.

The company has recently recruited works director James Vaughan who is mounting a charge to progress the business into a turned parts specialist where the newly installed Citizens play a key role to achieve a target of tripling the turnover with the same five employees who already run the firm through a seven day week 24h day regime.

And, already Vaughan has had his goals recognised with CNC sliding head autos contributing to the winning of one of two supplier credibility awards from a US customer, a certification that is highly sought after by its 120 suppliers.

The reason Harrison developed the probe and tool sensor was that he used proprietary probe systems on his machining centres and milling machines but maintains: "Like many users I was frequently damaging the stylus by running the probe into the job".

"I reckon that any electronic device fitted to a machine tool should be rugged enough to stand abuse".

"So I decided to develop my own which is considerably more competitively priced than others on the market." His probe and tool setting sensor has been designed for use on machine tools having an over travel of 6mm in each of the X, Y and Z axes.

It has a repeatability claim of better than five microns and has a robust shank 20mm long is able to access difficult areas using a 6mm diameter probe tip with flats rather than the traditional sphere.

Mill/turned parts will only now be produced on the two Citizen machines which will provide the extra capacity required for more difficult single cycle work to replace an existing four year old sliding head auto described by him as: "Not one of the best purchases I made." Vaughan supports the statement offering that the Citizens were immediately more impressive and as an example, the first job set up on the C16 did not require an offset adjustment for four days even while running around the clock".

""The machine it replaced would move 0.04 to 0.05mm every time the guard was opened," he says.

The C16 was the first Citizen machine in the UK to feature the oversize bar capacity of 18mm, "Just in case," says Vaughan, covering a capacity between 8mm and 18mm.

It also had the first duplex opposed head driven toolholder which enabled endworking at both the main and subspindles from a single tool position with cutters up to 8mm diameter.

It has a depth capability of up to 30mm in each direction.

The capacity of the M32 overlaps the C16 holding a bar size between 12mm and 32mm, it also has the 2000 lb/in2 CoolBlaster, high pressure coolant system, a programmable part retrieval system to clear working area and NC Engineering's Alarm Alert automatic call-out.

This is fitted to both machines should problems occur when running in lights out mode, and calls the duty operator on either mobile phone or land line giving details of the machine stoppage such as material shortage or process malfunction.

The tool capacity of up to 82 tools was important to Vaughan on the M32 because he is practising fast changeover techniques, leaving the machine set with common tools and grouping like materials and similar parts together.

He also maintains the machines were selected in order to provide a practical single cycle 'one-hit' solution to account for any feature, geometric tolerance or surface finish requirement set by the customer.

Already Microform Precision Engineering produces a wide range of parts in Delrin, plastics, aluminium, brass and stainless steels".

""You need flexibility and we have turned to a new chapter in our business to provide a finished part from the one machine".

"Previously, we had wasted hours on secondary operations and the associated problems," Vaughan maintains.

Vaughan and Harrison both firmly believe that delivery, quality and service are key: "You ca not ring the Far East and ask for panic order parts in two or three days, that is our delivery objective and we have now planned with the tooling set-up to be able to split, say a 5,000 batch, set-up for a few hundred parts against a special order and quickly switch back to the original CNC program and contract." That has meant a considerable spend on tooling to give flexibility but he confirms even deburring is simple on the Citizens: "You just program the interpolation required to take off a whisker around the profiles and the job is done, ready for washing," says Vaughan.

He is a great believer in the use of form tools and makes a lot of his own such as flat form tools step and combination drills.

This enables him to combine undercuts, grooves and diameters, chamfer and counterbores and combination drill cross holes.

Often one tool will do a whole series of parts which saves cycle time from tool indexing and having to perform multiple passes".

""It also helps when simultaneous cutting with a form tool when up to three tools are engaged at the same time enabling several features to be produced very quickly," he says.

The use of CoolBlaster follows the success of other Citizen M32 specifiers with tool life extended by at least 50% on 316 stainless steel, peck drilling eliminated and the benefit of much better swarf control.

Most important is the secondary collet cleaning between parts plus the bonus of cycle time improvement by up to 20%.

Among the jobs now falling under the single operation philosophy is a pin assembly for off-road vehicles.

This 75mm long 6mm diameter shaft with circlip grooves used to have to be ground to 15 micron tolerance with serrations produced in the centre for push fit assembly to a mating block.

Now the pin is made complete in one operation with a knurl in the centre which has been accepted by the customer.

Altogether, some 30s have been saved on production of the part.

A balancer shaft for a fuel injection system has been cut from two to one operation and a square flanged component with a spigot, central bore and four drilled and tapped pitch circle holes has shown a massive 70% saving on production times by combining four operations into one.

Cutting with three tools simultaneously the round bar is milled square, the centre bore drilled and bored and outside diameter of a spigot turned before a special ground subland drill is used to drill and countersink the four holes and interpolate around the part to provide a precision deburred edge.

But the classic is a medical industry connector made from 24mm diameter 316 stainless steel bar which has an offset eccentric bore that required a total of six operations to produce.

Previously production methods were made worse because tight process tolerances had to be applied to ensure fixturing would reproduce a blended milled form which then had to be finally polished by hand.

This part is now produced in one single cycle with all geometric relationships easily met, size and surface finish are now regarded as 'as machined', which eliminates all the additional handling, fixturing, inspection and polishing.