Carlisle-based Bendalls Engineering has an established reputation as a manufacturer of pressure vessels and specialist steel fabrications.

Machining is a relatively new addition to the business, following the acquisition by its parent company — the Carrs Group — of Clive Walton Engineering and the relocation of the latter’s machine shop to Bendalls in 2012.

Clive Walton had been a long-term customer of Sheffield-based WNT (www.wnt.com) — part of the Ceratizit Group — and that relationship also transferred, with WNT’s Matt Darbyshire continuing to provide sales and technical support to Bendalls.

While well known for its extensive range of standard cutting-tool products, WNT also has a dedicated team designing and developing tooling for special applications; so when Bendalls won a contract to manufacture a series of venturi-type pumps that would be used in the testing of highly radioactive high-pH nuclear-industry ‘liquor’, WNT was asked to become involved.

The key features of these 316 stainless-steel pumps, which need to be machined to high levels of tolerance and surface finish, include a series of relatively small-diameter bores with high length-to-diameter ratios.

Machining features such as these was unknown territory for the team at Bendalls, and the project was further complicated by the lack of high-pressure coolant on the available CNC lathes.

Machining engineer Stuart McCubbin said: “We looked through the standard tooling catalogue but could not find anything suitable for our requirements, so we called in WNT’s Mr Darbyshire, gave him copies of the pump drawings and asked what special tooling WNT would recommend. The company quickly returned with a full proposal and tool drawings.”

Cutting trials

With multiple drills, tapered boring bars and reamers involved — and not one tool being standard — Mr Darbyshire made himself available for the initial and complex cutting trials; the difficulty of the machining was such that one feature took a full day to machine.

A further complication was the lathe’s limited Z axis, which needed to be used to its maximum to accommodate tools up to 312mm long — and just 15.3mm in diameter in some cases.

Due to these lengths, and the need for a good surface finish, the tools were manufactured from solid carbide, with WNT’s MiniCut inserts (with 0.2mm corner radii) fitted to the boring bars.

Peter Norman, Bendalls’ machine shop foreman, said: “This was a learning curve for us, and there was an element of trial and error — changing insert corner radii, for example, to achieve the required surface finish. Working with WNT, we achieved the results we wanted.


“Part of the development process necessitated ‘thinking outside of the box’ and using grades — particularly for drilling — that wouldn’t normally be the first choice.

On some of the WNT Quattro-style drills, a steel grade of carbide was the only available option; in theory, it was far from ideal for our application but it worked, thanks to the team pooling ideas, which included taking the coolant concentration up to 12% to aid lubrication.”

Due to the nature of the project and its end use, documentation of the whole process was important for both the machined parts and the final welded assembly.

Bendalls’ Ian Willacy said: “When the machined parts are welded, they have to maintain very tight — in welding terms — concentricity and alignment, and that pushed the welding techniques to new limits.

All of the parts and assemblies had to be photographed using a £30,000 bore camera, such was the importance of maintaining the tolerances and surface finish throughout the length of these long bores.”

Tony Pennington, managing director of Ceratizit UK & Ireland, said: “While our standard WNT catalogue contains over 56,000 product lines, it can’t always provide a solution to a customer’s specific requirements.

"Our investment in the design and manufacture of special tools — such as those implemented at Bendalls — is testament to the commitment that the Ceratizit Group makes to providing a cost-effective and practical solution to meet the needs of customers.

"We then back up that design and manufacture with the support at the machine to ensure that everything runs as smoothly as possible.”