| Hi Alan,
The way I have always done mine is with a milling slot drill.
Just drill your hole as normal, then swap over to the milling bit just slightly larger than the head of the bolt and gently plunge down until you reach the depth required. You can only do this if the bit you are machining is tightly held in a vice otherwise the job tends to end up blood red.
Another way is to find a source of what used to be called bullet point drills, used mainly for sheet metal work, they don't snatch when you break thru. What you do with those is to drill the hole for the head first then finish off the thru hole.
John |