EH Thompson, which trades as Thompson Precision Engineering, regards itself as an industrial problem solver rather than an engineering business.
While it undertakes what may be classed as general sub-contract work, the company — founded in 1939 as a scientific-instrument maker — specialises in a wide variety of challenging project-based work involving design, machining and finishing.
An ability to solve problems has been part of Thompson’s make-up from the outset; no sooner had the company started manufacturing scientific instruments than it had to turn its skills to manufacturing munitions and other defence hardware, as World War Two took hold.
After the war, Thompson needed to replace this volume production and subsequently became a key supplier to Ford Motor Co.
The manufacture of high-pressure hydraulic systems was later added, but global competition began to take its toll on Thompson’s business in the 1980s, prompting a shift in focus to high-precision aerospace manufacture — mainly safety-critical parts.
The company used to sub-contract some work to JH May, a pattern maker and prototyping specialist, which it purchased in 2003.
Thompson’s managing director, Simon Terry, says: “The resulting business combines the best of high-precision engineering and bespoke project manufacturing; it allows us to work with larger companies needing to get things done quickly.
“Many of our customers rely on us to confirm that their design concepts are feasible to manufacture; as a result, we get most of our enquiries from design offices.”
Thompson’s versatility is highlighted by two current projects. One is a commission to build a full-size replica of the Lockheed 5B Vega high-wing monoplane used by Amelia Earhart in 1932 to fly across the Atlantic Ocean and then non-stop across the USA.
This replica will comprise wood, fibre glass and aluminium and will eventually go on display, hanging 30ft above the ground. The second project is more engineering-based and involves machining a series of architectural components from billets of 316 stainless steel.
The largest billet weighs 3 tonnes, with just 0.5 tonnes remaining once machining is complete.
With such large volumes of material being removed, and the high value of the parts being machined, a review of milling strategies was called for; Thompson turned to the Sheffield-based tooling company WNT (UK) Ltd (
www.wnt.com) for assistance.
Ian Cain, Thompson’s production manager, said: “The roughing cycle for the largest piece involves many hundreds of hours of cutting, followed by a series of finishing cycles that each take more than 100hr.
“These protracted machining cycles mean we need to be confident that the cutters we use can safely operate ‘lights out’.”
Another challenge faced when machining these pieces is the tool extensions that are required. For rough machining, the button-style cutters need a ‘gauge length’ of 250mm; for finishing, this has to be extended to 350mm.
Working with WNT’s technical sales engineer, Adam Cross, a machining strategy was developed that would allow ‘lights out’ machining with the support of sister tooling.
Mr Cain said: “Good and consistent tool life are key in this project.We have to know that the cutters will last a certain amount of time, so that we can leave the machine running unmanned; this is not often done when machining 316 stainless, but the length of the roughing and finishing cycles necessitates it.
“Mr Cross has helped us achieve this; and while we were not chasing seconds on cycle time, we are still achieving very competitive performance for such a testing application”.
For both the roughing and finishing operations, WNT suggested its Dragonskin HCN 5235 grade of indexable insert, which has been designed to deliver significant cycle-time reductions when machining stainless steel and heat-
resistant alloys.
Mr Cross said: “With cycle time being less of a priority, we focused on getting tool life to a point that we were happy with.
“That said, using the WNT System 2510 RS 100mm-diameter button cutters with RPHX 1204M8EN-M31 HCN 5235 inserts, we are able to use a cutting speed of 186m/min and a feed per tooth of 0.35mm.
“To assist with the tool life, we also run the cutters dry, as applying coolant would introduce an element of thermal shock and reduce the life of the inserts.”
For the finishing operation, a WNT System K 2000 32mm copy milling cutter with ROHX 3250 R16-FM3 WAN2210 inserts is used. The tool life for these cutters on the finishing cuts is particularly good when running at 200m/min and a feed per tooth of 0.15mm.
In conclusion, Mr Terry added: “The surface finish on the end product is very important, so the tools have to be super-accurate; we can’t have any mismatch when sister tooling is called up.
“This project is typical of what we achieve on a regular basis, and the partnership with WNT ensures that we use the machining criteria needed to deliver parts to specification.
“For this particular stainless-steel project, we also bought a new EC1600 horizontal machining centre from Haas, to ensure we had the machining capacity.”