Turned parts sub-contractor continues expansion

Simon Dawson, DPC managing director, in front of a line of 20mm capacity Citizen Cincom sliding-head lathes, with two 12mm capacity models at the far end

The installation at Dawson Precision Components (DPC) of a Citizen Cincom L20-XLFV sliding-head lathe earlier this month brings the sub-contractor’s tally of CNC turn-mill centres to 21, most of which are bar fed and have driven tooling. The high-precision turned parts specialist, which is required by some customers to hold tolerances down to single-figure microns, also operates three vertical machining centres (VMCs) mainly for second-operation work on larger turned components.

The additional Cincom lathe, supplied by Bushey-based Citizen Machinery UK brings the tally of sliding-head lathes, as distinct from fixed-head models in the Oldham factory, to nearly three-fifths or more, if a Citizen Miyano BNA-42GTY is also taken into account. It is a hybrid fixed/sliding-head lathe capable of operating like a slider in guide bush-less mode, with the headstock able to move in and out of the working area.

The sub-contractor has been growing organically since the 1970s and has expanded its factory four times, most recently in 2024 when the shopfloor was increased by nearly 50% at a cost of £1.2 million. In the early days, the company fulfilled contracts mainly using single-spindle cam autos, but these had disappeared by the mid-1990s to make room for CNC fixed-head lathes.

Turn of the millenium
It was not until the turn of the millenium that the first three CNC Cincom sliding-head lathes were installed, all 20mm capacity L20-VII models that initially were devoted to producing large volumes of body jewellery from titanium bar. As is nearly always the case, once such capacity is available the work builds up and sliding head contracts now account for a majority of the company’s throughput.

Mr Dawson with works manager Tony Hughes

Several 12mm capacity Citizen Cincoms have also been purchased, the latest being a pair of L12-VIIs which arrived in 2014. There are also 38mm capacity models on the shopfloor, the most recent an M32-VIII installed in early 2023 which features an expansion kit that allows it to produce parts from bar up to 38mm in diameter.

The newer sliding-head turn-mill centres benefit from the ability to remove the guide bush in about 30min, allowing better accuracy to be achieved when turning components, particularly with regard to concentricity. This approach is ideal for producing components that are shorter than nominally 2.5-times their diameter and has the added benefit of considerably reducing the bar remnant length.

This not only saves cost, but also allows more components to be produced from a single bar, so the guide bush is removed for as much as 10% of production on the seven Cincoms in Oldham having the facility. A further advantage of guide bush-less operation is that the use of rolled bar whose diameter varies by up to 0.2mm can be tolerated, whereas sliding-head operation normally requires the use of ground bar accurate to within 30 or 40µm.

To get around this problem and enable less expensive bar of lower quality to be used for traditional sliding-head turning, a JBS compensating guide bush has been fitted to the latest L20-VIIILFV and DPC has retrofitted another one to a similar machine installed in 2022. The bush continuously compensates for variations in the diameter of the bar as it advances into the machining area, leading to high machining accuracy, repeatability and process reliability. Another advantage of the JBS system is its ability to dissipate heat generated when machining tough alloys, reducing even further the possibility of material seizing within the guide bush.

LFV software a key feature
A wide range of materials is machined by DPC for customers in the medical, life sciences, space, defence, communications, rail, motorsport, leisure and other sectors. They include plastics like PTFE, PEEK, acetal and nylon, which collectively account for up to 15% of production output. The ability of Citizen’s LFV operating system software to break what would normally be stringy swarf into short, manageable chips is a key reason for the sub-contractor choosing the chipbreaking option on its three latest Cincoms, as well as the Miyano.

The latest 38mm capacity Cincom sliding-head lathe, an M32-VIIILFV, arrived on the shopfloor in Oldham in early 2023

It is similarly effective when turning copper and numerous types of aluminium, while stainless steel, titanium and brass are also regularly processed at the factory. General tolerance stipulated on drawings is ±0.1mm, but some medical parts need to be machined to 5µm total. Usual batch size varies from 5 to 200, but exceptionally can be up to 20,000. Production is over a flexible shift pattern, including long periods of autonomous running. Lights-out operation is avoided due to the often tight tolerances that need to be achieved.

Mr Dawson said: “There is no doubt Citizen lathes last a long time – we have one on the shopfloor that is still producing components and holding tolerance after 25 years. Our policy, though, is to replace them regularly to take advantage of the higher productivity that modern, faster machines allow, as it makes it easier to compete for new work. With the high cost of electricity these days, reduction in power consumption is becoming ever more important.

He concluded: “Thankfully, contemporary Citizen lathes with their advanced ecological features are more economical to run than earlier models. We have just had solar panels fitted to our factory, which provide about a third of our electricity consumption. These measures are helping us reduce costs and will make us even more competitive going forward.”