The manufacturing specialisation at Thorlabs’ Ely bridge lies behind the installation of a large-capacity 24 hp/200-8,000rev/min XYZ BRM 60-200 CNC bridge mill supplied by XYZ Machine Tools.

This fixed bridge/moving table machine tool is equipped with a 1,600 x 5,080mm table and has a positional accuracy over 300mm travel (5,080mm - X axis/1,559mm - Y axis) of +/-0.025mm and a repeatability of 0.01mm.

The XYZ BRM 60-200 CNC bridge mill features a high torque vector driven spindle that can be serviced by an optional 24-station carousel-type toolchanger

The XYZ BRM 60-200 CNC bridge mill features a high-torque-vector driven spindle that can be serviced by an optional 24-station carousel-type toolchanger.

However, the requirement at Thorlabs mainly involves drilling and tapping hundreds of locating holes in large-scale optical tables/optical breadboards.

This is why the new machine is equipped with what Harry Southan, quality and process improvement manager, describes as a ‘wine rack’ holding imperial and metric multi-tool drilling and tapping heads, each weighing 15kg.

This tool cradle is located on one end of the machine table, with a change of multi-tool head taking around 30sec under full CNC control.

Optical tables/optical breadboards must provide a rigid and vibration-free base for experiments that could be adversely affected by small vibrations, while also allowing optical equipment to be mounted and positioned with a high degree of accuracy.

According to Thorlabs, the best overall performance of an optical table is achieved by a sandwich of clad metal honeycomb, which can be up 310mm in thickness, with the 6mm thick top plate (or breadboard) drilled and tapped in an imperial or metric grid pattern.

‘The new bridge mill has since given us the performance that we were looking for when machining mainly stainless steel and some aluminium and, less frequently, non-magnetic steel, which is a lot tougher to machine,’ said Southan, ‘We have also achieved optimum drilling speeds, although tapping is currently a limiting factor,’ he said.

‘However, we are switching from 4- to 8-bit tapping heads, which weigh 22kg, to virtually half the time currently taken to tap the drilled holes,’ he added.

XYZ BRM CNC bridge mills are designed for light to medium milling applications and, having a substantial fabricated rather than cast structure, weigh and cost considerably less than traditional designs of heavy-duty bridge mill.

Their design also eliminates the need for special foundations, minimising installation time, requiring less floor space and providing a high-performance alternative to a router.

XYZ contributed applications assistance throughout the project, which included extending the X-axis travel specification of a standard BRM machine, implementing the multi-tool head-change system and installing wall-mounted, pneumatically operated pusher systems that ensure the plates/boards are positioned flat to the machine table prior to final clamping and machining.

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