Those involved in the agricultural industry expect any equipment they invest in to be robust and effective, as their livelihood depends on it. Based in Bury St Edmunds, Shelbourne Reynolds Engineering designs and manufactures world-class equipment for this diverse sector.
The majority of the company’s ground-care, harvesting and livestock products are produced at its 90,000ft2 facility. Around 120 staff are split between machining, sheet metal, assembly, welding and painting; and although the company is currently adding 20,000ft2 to its covered floor area by developing its external goods area, it is effectively ‘land-locked’, so any increases in throughput must come from technology. Regular investment in new CNC machine tools and new processes helps the company to keep pace with global competition — and meet the growing demand for its products world-wide.
With 70% of Shelbourne Reynolds’ production exported to countries that include North and South America, Australia and New Zealand, as well as Eastern Europe, each product is developed for a global market-place. Sales director Neil Smith says: “Our new 42ft stripper-header was designed for customers in the USA and Australia. Previously, our largest was 32ft wide, which was the largest machine for nearly 10 years. That was the most popular size, so it was fairly obvious that there was a market for a bigger unit. We started developing the 42ft unit about four years ago with a view to future-proofing our stripper-header product range. This new unit did present some problems, as the factory was originally designed around manufacturing 20ft units.”
The wider 42ft stripper-header, like all of the products in this range, features a variable drive system that allows the agricultural-machine operator to alter the rotational speed of the stripper head. Two conical wheels are connected via a large V-belt, and the position of the belt across the wheels determines the speed. The wheels are located on precision-machined hubs, manufactured from EN24 high-tensile alloy steel in batches of 24.
Threading problem
Machine shop supervisor Dave Hovells says: “The hubs require six equally spaced 45mm-deep standard M8 threaded holes, which caused us significant problems. The pilot hole was drilled to depth on a CNC machining centre, but we could only reliably run the rigid tap down to 25mm; the rest of the thread had to be produced manually on the bench, which often resulted in taps breaking in the hole.
“Hubs with taps broken in them had to be sent off-site to have the tool removed by EDM machining, at a cost of £60 per tap. In a batch of 24 hubs, we would average two broken taps; and even after the taps had been removed, we still had to produce the thread.
“We were losing so many man-hours. Moreover, we would have everything else ready for assembly but be waiting for a hub that was somewhere else, being re-worked. This happened on a regular basis and prevented us from keeping up with demand. Everything was held up until the hub came back, and we were always behind. Moreover, because we were under pressure to get the hub done, we tried to work a bit quicker, which often saw us break another tap and push the production schedule even further out.”
Size considerations
The solution to Shelbourne Reynolds’ production nightmare came from Martin Pryor, a sales engineer for Chesterfield-based Dormer Tools Ltd (
www.dormertools.com), who suggested using the company’s E294 thread-forming tap. Mr Hovells says: “At that time, we were considering changing the design of the hub to incorporate a larger M10 thread, as the heavier tap would be less likely to break. However, changing to the larger thread would also mean altering the pitch diameter of the threaded holes. This would have presented a problem when it came to suppling replacement parts in the field. It was a very serious consideration at the time; we were almost at the point of changing, but
we decided to try the Dormer solution first.”
Mr Pryor says: “At Dormer, we modified the shank of the E294 thread forming tap to get the depth required. Initially, we tried it in a test piece to make sure it was successful; we set it up with a piece of EN24 so the tap was rolling the thread in a like-for-like material. When that test proved successful, we got the ‘green light’ to try the tap on a production part. We then had to test how many holes we could thread before the tool failed. That first tap did the whole batch without any breakages.”
The production team at Shelbourne Reynolds monitored the continued performance of the tap; it eventually failed after 350 components — 2,100 deep formed threads. “In a hard material like this, at such a depth, the life expectancy was an unknown, but it has proved to be extremely efficient and effective,” says Mr Pryor.
Bespoke macro
A macro sub-routine on the CNC machine is called up to apply the parameters for forming the deep threads in the hub at 650rev/min; and because the material is being rolled (or flowed) into the form of the thread rather than cut from the parent material stock, it results in a stronger thread. As well as the direct savings in labour time and re-working, the Dormer E294 thread-forming tap has also allowed Shelbourne Reynolds to improve its process efficiency.
Mr Hovells says: “Previously, we applied the carbornisation finishing process after all the machining operations had been carried out. This resulted in some debris being trapped in the threaded holes, which again required the thread to be chased out manually. Now we apply the finishing process prior to drilling and thread forming, so no further remedial operations are required.”
The E294 thread-forming tap is still a relatively new product, but the introduction of it to Shelbourne Reynolds’ machine shop gave Dormer the ideal opportunity to demonstrate its capabilities. Mr Pryor says: “We were keen to find an opportunity to test the E294 in a difficult situation, to show exactly how good the tap was. This was presented by Shelbourne Reynolds, and it has been a resounding success for both companies. The range now has six different roll taps in it, as we have added smaller M1.6, M2 and M2.5 taps.”
In conclusion, Mr Hovells says: “Our production started flowing again because producing the hub is no longer problematic — thanks to the E294 thread-forming tap. There is no need to run a tap down the thread to clean it after hard-coating the hub, there is no swarf created by the thread-forming operation, and there is no re-work caused by broken taps.”