Shelbourne Reynolds harvests production results thanks to Dormer’s thread forming technology

Based in Bury St Edmunds, Shelbourne Reynolds Engineering designs and manufactures the majority of its ground care, harvesting and livestock products at its 90,000 ft2 facility. Around 120 staff are employed, split between machining, sheet metal, assembly, welding and painting. Although the company is currently adding 20,000 ft2 to its covered floor area by developing its external goods area, it is effectively land-locked so any gains in productivity must come from technology. Regular investment in new CNC machine tools and new processes help the company keep pace with global competition and also help meet the growing demand for its products from farmers and landowners around the world.

With 70 per cent of its production exported to a wide range of countries, including North and South America, Australia, New Zealand and Eastern Europe, each product is developed for a global marketplace. As Sales Director, Neil Smith, explains: "Our new 42ft stripper header was designed for customers in the States 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 the market for a bigger unit, and we started developing it about 4 years ago with a view to future proofing that product range. It did present some problems as the factory was originally designed around manufacturing 20ft units and now we are putting machines twice that size through.”

The wider 42ft stripper header, like all of the products in this range, features an ingenious variable drive system that allows the agricultural machine operator to alter the rotational speed of the stripper head. Two conical wheels are connected with an extremely large vee 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. 

Machine Shop Supervisor, Dave Hovells, recalls: "The hubs require six equi-spaced 45 mm deep standard metric pitch M8 threaded holes, which caused us significant problems in production. The pilot hole was drilled to depth on the CNC machining centre, however we could only reliably run the rigid tap down to 25 mm. The rest of the thread had to be manually produced on the bench, which as you might expect often caused taps to break in the hole.”  

Hubs with taps broken in them had to be sent offsite to have the tool removed by EDM at a cost of £60 per tap. "Each hub was taking 20 minutes to produce, which equates to a lot of wasted man hours. In a batch of 24, we would average two broken taps, and even after the taps had been removed we still had to produce the thread,” Dave Hovells says.

He continues: "You are entering into the realms of double working everything, it was a nightmare. We were losing so many man hours, plus everything else was ready for assembly but you are waiting on that hub which was somewhere else being re-worked. It happened on a regular basis and we could not keep up with the demand, so everything was held up until the hub came back. We were always behind.  Again, as you are under pressure to get the hub done you try to work a bit quicker, you then break another tap and it was holding up the machine for the next job, so we were losing time there, pushing the production scheduling out.”

The solution to Shelbourne Reynolds production nightmare came from Dormer Tools’ Sales Engineer, Martin Pryor. He presented Dormer’s E294 thread forming tap. Dave Hovells recalls: "At that time we were considering changing the design to a larger M10 thread to provide a heavier tap less likely to break, and moving the pitch diameter to suit. This would have meant that in the field if they had required a replacement part we would have a problem. It was a very serious consideration at the time; we were almost at the point of changing but decided to try the Dormer solution first.”

Martin Pryor adds: "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. That test proved successful so we then got the green light to try it on a production part. We then had to test how many we could do before it failed, because of the depth of the thread. That first tap did the whole batch without any breakages.”  

The production team at Shelbourne Reynolds monitored the continued performance of the tap and 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 Martin Pryor. 

A macro subroutine on the CNC machine is called up to apply the parameters for forming the deep threads in the hub at 650 rpm. As 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 threaded solution.  

As well as the direct savings in labour time and reworking, the Dormer E294 thread forming tap has also allowed Shelbourne Reynolds to improve its process efficiency. Says Dave Hovells: "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.”

Still a relatively new product, the introduction of the E294 thread forming tap to Shelbourne Reynolds’ machine shop provided the ideal opportunity for Dormer. As Martin Pryor says: "We were keen to find an opportunity to test the E294 in a difficult situation: to see exactly how good the tap was. This was presented by Shelbourne Reynolds and it has been a brilliant success story for both companies. Today, the range has six different roll taps in it, and we have now incorporated smaller M1.6, M2 and M2.5 taps in the range building on the success of the initial performance release of the M3 to M16 roll tap range.”  

Dave Hovells concludes: "In a nutshell, thanks to Dormer our production started flowing again because this particular part was not giving anyone a headache anymore. With the hard coating there was no need to run a tap to clean the thread, there is no swarf created by the thread rolling operation and no rework caused by broken taps. There are no problems at all, just a quick set up and away you go.”