Nine Okuma CNC lathes and mill-turning centres ensure the quality of XTRAC's gear blanks, and their versatility has also enabled successful production of a wide range of components.Few people have heard of XTRAC outside motor sport but within the Formula One, World Rally Championship, Touring Car and Champ Car fraternities, the Thatcham-based company is renowned as the best in the business for the manufacture of gearboxes, differentials and gear sets. This has been achieved through an innovative approach to design and development, combined with a no-holds-barred attitude to investment in top quality manufacturing equipment and production facilities, including nine Okuma CNC lathes and mill-turning centres from NCMT. Not only do they ensure the quality of the basic gear blank, but the versatility of the most recent machines has also enabled successful production of a wide range of components.
XTRAC can supply anything from a discrete gear ratio set to a complete gearbox and transmission assembly for a Touring Car or Sports Car.
Many of the top Formula One teams use XTRAC gears and transmission components, while a number of World Rally Championship contenders commission entire four-wheel drive transmissions.
One obvious result of the company's success is its splendid new 88,000 sq ft factory at Thatcham, Berkshire.
Innovative though the company may be, XTRAC's reputation is dependent on getting the basics right.
For successful gear manufacture, roundness and parallelism have to be very accurate.
Quality manager Dave Neville comments, 'Maintaining tolerances at the blank stage is critical as it impacts on every subsequent operation.
Squareness and parallelism have to be within 0.005 mm, concentricity has to be better than 0.010 mm and bore accuracy has to be better than 0.020 mm.
'We also need good finish because we are combining light weight with maximum strength.
All of our gear generation processes depend on mandrel mounting.
Likewise we often cut gears in stacks and splines are broached.
If we want a top quality gear we need a precision blank, and that demands our using a quality machine to produce them.
'That is largely why we have continued to install Okuma machines since we began to use CNC turning about twelve years ago.
The machines are highly rigid, so maintaining finish is not an issue and their technology has progressed in parallel with our requirements.
They are also very, very strong; this is essential as many of the components we manufacture require significant stock removal so we need very robust machines to withstand continuous heavy use.' This sometimes has additional benefits as Mr Neville reports.
'Some time ago we had a collision which ripped the turret off one of the Okumas, shearing four 14 mm bolts in the process.
We might have expected to write off a machine after an incident like that but, in fact, it was back in production within a few days.
NCMT's service and support is usually good but on this occasion they really pulled out all the stops!' Production at XTRAC is entirely batch based.
Quantities vary from around ten-off on larger items up to 200-off on gear blanks.
The company subcontracts machining of some components but produces functionally critical parts and features in-house; all shaft work and blanks for bevel gears as well as short-lead-time requirements fall into this category.
Components are produced from either forgings or bar, depending on volume, function and complexity.
Blanks can be up to 250 mm diameter for differential case or final drive applications, while manufacture of gear change barrels demands shaft profiling on components up to 400 mm long by 75 mm diameter.
Most parts are produced from an EN36-derived material which is produced to XTRAC's own metallurgical specification to provide consistent properties during heat treatment.
Of XTRAC's Okuma machines, the three most recent acquisitions all have mill-turning capability.
The two LU-15M machines have twin turrets while an LB-10M is a single turret machine.
All nine lathes are programmed and set by their operators via the Okuma-built conversational CNC system.
Other than build quality and accuracy, this is held to be one of the major features in favour of the machines.
The turning shop at Thatcham is staffed entirely by programmer / setter / operators.
Mark Rowland, XTRAC's turning shop foreman, comments, 'We bought the first LU-15M to provide a single-hit machining capability and this has significantly speeded availability of some of the more complicated parts.
There is a regular requirement for blanks with lightening holes, for instance, while some of the gear change barrel work is well suited to production on mill-turning machines.
What goes where depends on striking a balance between the benefits of mill-turning and the faster cycles available when milling on a dedicated machining centre.' Where there is a large milling requirement, XTRAC will normally assign all of that work to a machining centre.
The driving force throughout is to achieve the optimum quality and finish in the most economic manner.
Mr Rowland concludes, 'Especially on the LU-10M we do some very intricate work.
In a way the machine is ideal for this type of 'toolroom' application as the combination of machine and control is very versatile.