Scott and Lars picked up on the Robobroach. These things are awesome...They are a set of Metric Robabroach by Hougen USA. The 18mm is the perfect size for this job and worked a treat. For those who haven't used these before they have a spring loaded centre which retracts as you start to drill and keeps everything centred. Great for clean, accurate holes in sheet metal.
I've added some images of these to my original gallery
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