– Dremel 3.4mm grinding stone for pilot dimple
– Masonry bit with clearance/rake ground on the end, slow speed & plenty of tapping fluid.
Story:
So I bought some 1mm thick spring steel strips to make some leaf springs from. I assumed drilling a hole in them would be similar to stainless steel – I was wrong!!!
After finding a centre punch has no affect on this material whatsoever, blunting and breaking a few drill bits and other tools I dare not mention, and even playing about with annealing the stuff in the desired area I hit the internet and collected information from various sources and tried the following:
As the centre punch had no affect, I created the pilot dimple using a Dremel with the 3.4mm grinding stone at an angle – need a good eye and a steady hand but fairly easy.
Drill bit – I read that carbide tools should be used but I reeled at the price especialy considereing what I had managed to do to my exiting tools. So I got my cheap masonry bits (local DIY store style) ground some rear clearance/rake for the swarf, being careful not to touch the cutting edge. Cut at a slowish speed with plenty of drilling/tapping fluid – job's a good'n!
As I went through quite a bit of frustration to get there I though I would share.
If you already have carbide drill bits then good for you! 
Edited By Thomas Gude on 01/03/2015 13:46:41