At the Market Overton factory of sub-contract machinist Hi-Spec Precision Engineering, five Hurco machining centres and various other machine tools are producing parts from mild steel, stainless steels, bronze, brass, aluminium and plastic over a single daily shift from Monday to Friday.

However, at the weekends, two of these machines take on a somewhat different role.

That is when Darren Grainger (Hi-Spec’s owner) and his brother Gavin indulge their lifelong passion for music by milling electric-guitar bodies from solid wood.

Initially, they used CAD files downloaded from the Internet; more recently, they have produced five designs of their own, including one for a bass guitar.

Moreover, this is a lucrative hobby, as some of the instruments sell (both at home and abroad) for up to £3,500 under the brand name Grainger Guitars (www.graingerguitars.com), which is owned jointly by the brothers.

Gavin Grainger said: “To produce the guitar bodies, necks and other parts from wood, we now mainly use a Hurco VM30i machining centre, and sometimes a smaller VM5i.

“Both are three-axis models that were installed in 2017, although we started the guitar business two years earlier, using other machines. We began selling the instruments in 2016 at exhibitions around the UK.

“All that is needed before starting guitar work on a Saturday is to wipe down the machine table and block off the coolant nozzles to prevent any ingress of sawdust.

“When we have finished profiling wooden components, we simply vacuum out any wood residue, clean down the machine and uncover the coolant holes; we are then ready to cut metal again on Monday morning.”

Various woods are used in the making of the guitar bodies.

The early materials were maple, alder and poplar, but the Grainger brothers have also used swamp ash, mahogany, ebony, wenge (a tropical timber that is very dark in colour and has a distinctive wood pattern), walnut, buckeye burl, limba, purpleheart and some wood/resin composites.

Pearl and stone materials are also machined on the Hurcos — supplied by High Wycombe-based Hurco Europe Ltd (www.hurco.co.uk) — for the marquetry inlays.

Cutters for aluminium

Router cutters were used at the outset, but solid-carbide end mills and ball-nose mills designed for machining aluminium were found to produce a much better result, as the sharpness of the cutters virtually eliminates burrs and produces a fine surface finish that is consistent with the final use of ultra-fine 2000-grit sandpaper (with an average particle diameter of 10µm) to smooth the wooden components before the application of multiple coats of gun barrel oil to achieve a lustrous finish.

Everything for the guitars is manufactured in-house, including all metal components — apart from the pick-ups and their associated electronics.

Unlike the wooden elements, the turned and milled metal parts are sold to other guitar builders world-wide over the Internet via another Web site (www.graingerguitarparts.com), which forms another profitable sideline.

Commenting on Hi-Spec’s main sub-contracting business, Darren Grainger said: “In 2015, we invested in a second five-axis machining centre from Hurco, a VM10Ui; at the same time, we upgraded the control software on a similar pre-existing model to the manufacturer’s WinMax 10 version.

“These five-axis machines are used mainly for producing components using 3+2-axis strategies, which are programmed conversationally directly at the control.

“Two years later, we installed the VM5 and part-exchanged a small Hurco VM1 machining centre for the VM30; this has a 1,270 x 508 x 508mm work envelope and allows us to produce larger metal parts for rock crushers.

“This machine is also the mainstay of wooden-component manufacture for our guitars.”

User interface

Darren Grainger added that the Hurco control system on the latest machines has a smoother and more-convenient touch-screen graphical user interface.

“Scrolling through fewer menus allows the operator to arrive at the required screen more quickly. Even a simple operation like entering a code to jog the axes while the doors are open is easier and no longer involves having to go through the diagnostics screen.”

In addition, WinMax 10 software enables faster cycles through the use of Hurco’s Ultimotion and Adaptipath control software, which has powerful look-ahead and optimisation capabilities that reduce cycle times — especially when milling the corners of multiple pockets.

The Tool Change Optimisation feature is also helpful, as it automatically rationalises the number of cutter exchanges for optimal efficiency.

Darren Grainger added: “We have been able to save a lot of machining time through a combination of the latest Hurco software and the use of trochoidal milling with solid-carbide rather than inserted-carbide end mills.

“In some instances, we have more than halved cycle times. For example, we produce batches of 38 puller ends for hydraulic tooling — two at a time — from EN24T billets in two operations on the VM30i in a cycle that previously took more than 4hr.

“Now, using a 12mm-diameter solid-carbide end mill with a 16mm depth of cut, a 6m/min feed rate and Hurco’s twin-nozzle coolant delivery — together with the standard air-blast facility, which incidentally is used on its own when machining wooden components — the same job takes about 2hr.

“In another case, the machining of a steel matrix that used to take 40 and 35min for ops 1 and 2 respectively has been reduced by an even greater percentage to cycle times of just 17 and 12min.”

Hi-Spec Precision Engineering is continuing to grow, despite operating with fewer staff than two years ago, so profitability is up.

The hydraulics sector accounts for around 40% of the company’s turnover, with frequently machined components being used in hydraulic actuators and valves, rock crushers and access platforms.

Automotive and agricultural parts are also routinely produced.

Batch sizes range from one-off to hundreds for prismatic machining, while production runs on the company’s six CNC lathes can be in the thousands. Its customers are located everywhere — from the south coast of England across to Norfolk and as far north as Scotland.