....if that doesn't work three other suggestions.
1) find a 14 mm diameter carbide burr,
2) wrap emery cloth round a mandrel and use in a power drill - this will take ages but should get there in the end
3) I have seen special cobalt alloy tipped drills at car shows and these are demonstarted by brilling through files etc. These might be hard enough. Somthing like...http://www.toolstation.com/shop/Powe...its/d80/sd1230 - dont forget to use some coolant - even a little oil will help to keep temp down.

Peter