Turning to a solution for archaic threaded parts

Sourcing rare specification Whitworth nuts and bolts led to DWS Engineering’s owner David Swaffield manufacturing his own and creating a successful business as a result. As PES discovers, the success is down to the company’s expertise using Citizen Machinery’s lathe technology. 

In 2006, entrepreneur David Swaffield started his own contract machining firm, DWS Engineering, in Crewkerne, Somerset after gaining a mechanical engineering apprenticeship at a nearby packaging machinery manufacturer.

He started out using manual machine tools, progressing to CNC prismatic machining in 2009 and fixed-head CNC turning the year after.

Frustrated at not being able to find pre-war British Standard Whitworth threaded nuts, bolts and other components for the family-owned 1923 Aveling and Porter eight-tonne steam roller he was refurbishing, he decided to make them himself, leading to the inauguration in 2017 of another company, Historic Threads. It was then that Mr Swaffield discovered the capabilities and production potential of CNC sliding-head lathes from Citizen Machinery.

During the Second World War, the diameters of Whitworth threads were reduced to save metal. It is easy to obtain later sizes, but the original larger varieties used to be scarce and difficult to source. That was until Mr Swaffield identified a business opportunity through his subcontracting activities and via Facebook groups run by steam-driven vehicle enthusiasts.

Now a vast range of legacy threaded components, from the biggest Whitworth to the smallest BA (British Association) size and everything in between, is manufactured by Historic Threads and sold on its website www.historicthreads.co.uk. This business now accounts for 60% of Mr Swaffield's turnover. Despite its recent inception, the company is probably the largest stockist and supplier of pre-WWII threaded components in the world.

Seeking the sliding head option

Although nuts, bolts, studs and pillars tend to have a small length-to-diameter ratio and can be satisfactorily produced on fixed-head lathes, Mr Swaffield learnt early on in his career of the benefits of sliding-head turning, namely that the gang tooling allows short parts to be produced faster and the lathes are additionally capable of turning shaft-type parts if required. His father-in-law owned a subcontracting company half an hour's drive away on the south coast of England and he was a prolific user of Citizen Cincom sliding-head technology.

In 2017, the first Cincom L32, purchased second-hand from Citizen Machinery, was delivered to Crewkerne. The 2001 machine was installed, levelled and aligned the next day by a Citizen engineer and is still producing thousands of nuts and bolts every week, albeit of low complexity due to the machine's lack of driven tooling. It was recognised that in-cycle milling and other prismatic operations would be useful for machining more complicated components in one hit, so a second-hand Cincom M32 of a similar age with live tools arrived in March 2021.

As with most sliding-head lathes, the Cincoms are capable of producing components from bar up to 32mm diameter, so a fixed-head bar-fed lathe of 65mm capacity was purchased from another source for manufacturing the larger sizes of historic nuts and bolts.

Then in March this year (2022), due to the steep rise in demand worldwide for the legacy threaded components, a third sliding-head lathe was installed, this time a new Cincom L32-VIII LFV. The modern machine design has advantages in that it has been supplied with an expansion kit to enable the nominal 32mm bar size to be increased to 38mm, allowing for instance a 3/4-inch nut to be turned from round bar.

An additional advantage is that the guide bush assembly can be removed in an hour to produce in fixed-head mode relatively short components that do not require sliding-head turning. Remnant lengths are substantially shorter, reducing material wastage and costs.

Shortly after the machine was delivered, Mr Swaffield received DWS Engineering's biggest ever single order for the supply of brass, aluminium and stainless-steel parts from 10 to 20mm in diameter for use in the assembly of make-up brushes and pencils.

Frequency control of swarf

The latest Cincom is ideal for fulfilling this contract. For example, the low frequency vibration (LFV) chipbreaking software built in to the control is able to avoid stringy swarf when drilling a 100mm long, 8.5mm diameter hole down the centre of a 10mm diameter stainless steel pencil, even though the machine is not fitted with optional high-pressure coolant.

LFV is also proving useful in avoiding bird-nesting when producing plastic components, such as a batch of 2,000-off, 20mm diameter black Delrin spacers that went through the shop recently. The chipbreaking function is programmable, so it can be switched on and off by G-code in the cutting cycle. It may therefore be stopped during parts of the cycle where it is not needed, avoiding the slight material removal rate penalty due to the short periods of air cutting when the tool tip oscillates away from the component surface to break the swarf into short chips.

Users tend to employ LFV differently to suit their requirements; Mr Swaffield always makes sure it is switched on during parting-off, for example, as it results in a big increase in the life of the indexable inserts.

The chipbreaking function on the latest Cincom is also proving useful for producing in one hit, in a four-minute cycle, various EN16 stems for six sizes of patent-pending staple driver Mr Swaffield invented while he was bored during the 2020 lockdown.

LFV provides more latitude when selecting feeds and speeds, as even EN16 can generate stringy swarf unless parameters are set exactly. This new side to the business – www.stapledriver.co.uk – looks set to generate further significant sales revenue. In addition to being sold online, Mole Valley Farmers is stocking the product on a trial basis in 10 of its 55 stores around the country.

Citizen Machinery
www.citizenmachinery.co.uk

DWS Engineering/Historic Threads
https://historicthreads.co.uk