Frank Clifford, managing director of contract machinist, Genhart Precision Engineers, operated cam-type sliding-head automatics extensively in the early 1980s. He later developed his Cheltenham company's turning expertise using fixed-head CNC lathes. Now he has gone full-circle with the acquisition last summer (2011) of the subcontractor's first CNC slider – a Star SR-20RIII.
A feature of Genhart's business is its focus on very high accuracy work. Better than 5 microns total tolerance has to be held consistently on parts that Mr Clifford describes as 'fiddly', without recourse to lapping or other finishing processes. Aerospace, F1, telecoms and oil/gas exploration companies are typical recipients of the components, which are manufactured in anything from Nimonic, Inconel, high-nickel coppers and stainless steel through to brass and aluminium.
Solenoid valve manufacture is a notable area of expertise. It was one such component, made from 17-4PH stainless steel, that led directly to the purchase of the CNC sliding headstock, multi-axis mill-turning centre.
Specifically, the SR-20RIII bar automatic was equipped with a special angle drilling head that has helped to cut floor-to-floor time for producing a particular valve part by three-quarters.
Star GB's engineers helped to develop the application, even to the extent of loaning the angle head at the outset to prove its effectiveness. The component formerly required four separate operations – fixed-head turning, milling, drilling and deburring – entailing a considerable amount of inter-machine handling and risking tolerance build-up.
The part, which is complex, is now produced in one hit on the SR-20R III, including the angled hole, resulting in a significant reduction in production costs. Similarly, simple brass components are produced complete in cycles as short as 90 seconds, adding value without increasing manufacturing cost, particularly as such jobs can be left to run unattended during ghost-shifts after working hours.
The savings have prompted Genhart, a 25-employee company founded in 1979, to transfer many jobs from fixed-head CNC lathes to the slider, a process that is ongoing. Being able to turn near to the guide bush promotes the high accuracies that the company needs to achieve. Additionally, some shaft-type work such as hydraulic spools that previously had to be turned away, or subcontracted, is now done in-house.
Mr Clifford commented, "Learning to program the Star proved to be straightforward. We sent three operators on a training course provided by the supplier and they all picked it up quickly.
"We also find the lathe quick to set up and retool for the next job, lowering economical batch sizes. Before we bought the slider, our perception was that both of these aspects were going to be more difficult. Cheltenham seems to be a hot spot for Star lathe users, so there were plenty of places nearby where we could see similar machines working before we took the plunge."
Genhart has been so pleased with its first sliding-head lathe purchase that it has placed an order for a second Star SR-20R III.