Stepping up a gear

The Tunbridge Wells-based company specialises in hobbing, shaping, skiving and grinding gears with a PCD (pitch circle diameter) ranging from 4mm to 400mm and with modules from 0.25 to 5.0. The mainly bespoke products are produced to JIS, DIN, ANSI or customer specification.

The German-built Traub TNX 65/42 lathe with twin opposed spindles and 65mm bar capacity is equipped with an LNS magazine capable of feeding sawn billets or bars up to 1,600mm long. At the output side, an integral arm removes each finished component from the counter spindle and places it onto a conveyor.

The robustness of this arm allows it to handle the heaviest component in the family of shafts, weighing 3.5kg, while its generous travel means that finish machined components up to 400mm long can be pulled clear of the counter spindle. No other machine shortlisted by the subcontractor was able to match this performance.

Tony Smith, managing director of Muffett Gears and grandson of the founder comments: “We were turning the pump gear shafts from 45mm and 50mm diameter steel bar on a single spindle, single turret lathe, but were struggling to keep up with demand from our customer.

“We needed to increase output and initially looked at retrofitting a robot to one of our existing lathes. However, we decided to add extra capacity and invest in a new turning centre requiring minimal attendance from a machine operator.

“Geo Kingsbury’s response to our enquiry was prompt, following which we visited Traub’s Reichenbach factory a couple of times to see the machines being manufactured.

“Although the TNX lathe is available with four turrets, we established that optimum price to performance for our applications would be obtained using a turn-mill centre with three turrets. A suitably specified TNX lathe was installed in our Tunbridge Wells facility in September 2015.”

The machine was supplied by sole agent Geo Kingsbury as a turnkey package with component unloading mechanism and conveyor, bar magazine, various component programs, some of the required tooling and training for the subcontractor’s operators.

The pump gear shafts are turned from 300mm to 400mm long sawn billets of black bar. Operations include turning multiple diameters, producing a circlip groove and cutting a longitudinal, semi-circular key near one end using a Woodruff mill. Nearly 1,000 components per month are required across the family of parts, so batch size is around 100-off.

Productivity has increased substantially, as now to complete operations on the front end of the shaft as well as on the reverse after synchronous pickup by the counter spindle, the cycle time has been reduced to four minutes. Previously, on the single spindle lathe, turn-milling took a total of 12 to 15 minutes and additional time was needed to invert the component manually in the spindle for the second operation.

Mr Smith adds: “Now that the new production process has been established for the hydraulic pump gear shafts, we have started to turn other components on the Traub lathe in a variety of materials, including stainless steel, in batches of up to 600-off.

“Many of our products are ground after turning but some are not, so we need high dimensional accuracy and good surface finish on turned diameters. The Traub lathe allows us to meet those requirements and achieves very tight tolerances measured in microns.”

A highlight of the 10 tonne TNX65/42 is the heavily ribbed, cast iron, slant bed construction that dampens vibrations and promotes close tolerance machining. In addition to travels in X and Z of 650mm and 175mm, there is ±40mm of Y-axis movement on each turret. The synchronous main and counter spindles, each with C-axis, are of identical rating at 24kW/5,000rpm.

Control is provided by the TX8i-s running Traub's in-house developed software, optimised for the manufacturer's lathes. Realistic 3D simulation shortens set-up time and avoids collisions when producing first-off components.

Muffett Gears www.muffettgears.co.uk

Geo Kingsbury www.geokingsbury.com