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Barker Collins has machined 100 pairs of large clevises for offshore platforms.

Its CNC horizontal boring machines offered machining envelopes of up to 3000 by 2000 by 1300mm in X, Y and Z axes.

Chris Carter, managing director, said: ‘Rather than turn a 1m diameter, we interpolated the diameter on the five-axis horizontal borer, milled the face and an adjacent large-spigot diameter, then drilled a series of 36 holes of 20mm diameter on a pitch-circle diameter on the flange.

‘The table was then indexed and the main clevis bore was rough and finish bored through twin flanges that form the outer connecting yoke of the component.’ He added: ‘Similarly, on a mating end cap component, in addition to producing the main bore some 350mm diameter through the forging, the machine table was indexed 90deg to face and bore a large spigot, followed by threadmilling in the bore for a critical M280 x 4P-6H thread some 300mm deep.

‘The process had to maintain a surface finish within 1.6um Ra on the flank of the thread.’ On both components the operator made use of a Renishaw probe to inspect the machined component in-situ on the machine table and every sixth component was moved to the company’s large-capacity (3000 by 1200 by 1000mm X, Y Z) coordinate measuring machine for 100 per cent inspection, and the results were compared between machine readout and the CMM.

In order to inspect the surface finish requirement on the flanks of the thread, a Tesa Rugosurt unit was used to confirm the quality of the thread milled surface.

The unit was set at 90deg to the pitch line of the thread and the stylus was run down the flank into the root of the thread.

Carter said: ‘As a result, we set out operational methods, determine fixturing to support the part correctly to eliminate vibration and distortion.

‘Then we set about developing the tooling and the machining program before deciding how the part is going to be measured and qualified.’ In another example, Barker Collins devised a method that would enable the part to be machined complete in 25 hours when competitors had been quoting production times of almost four times longer.

Barker Collins Engineering

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