Ok so I showed how I make Hex recesses using a 'rotary broach' which I also showed being made. http://www.mvagusta.net/forum/showthread.php?t=48542
This tool has it's limitations though...as 'broaching' anything above 5.5-6mm hex puts a lot of 'load' on the lead screw/ rack and head bearing of the reasonably small engineering lathe I have. Therefore I have developed a 2nd technique which is very effective (in fact I use this technique most!)..although it too has it's limitations (due to the opening capacity of the vice jaws).....in which case you could use a small 'press'.
It involves making 'broaches' in a similar way to the last but using sections (50mm) of 10 & 8mm allen keys. And some re-machined brass plumbing 'stop ends'..from your local hardware (home depot...B&Q..etc).
As before the 'broaches' are 'dished' ...machined and 'tapered' to achieve the 'end' being 3% larger than the required 'hex'...eg 5mm hex needs a 'broach' 5.15.......6mm hex needs a 6.15 broach.
A corresponding hole (again 3% larger) is bored into the work piece...then 'chamfered'.
The 'broach' with it's 'machined' plumbing fitting (removal tool) together with the 'workpiece' are then 'pressed' together in a sturdy vice. The end of the 'broach' is then held between the jaws of the vice and two spanners used in opposite directions on the 'brass removal tool' and the task is complete.
Below are some shots of the manufacture of this system..it's operation in creating an 8mm 'hex'...and my 'box of tricks' ..all home made for this process which I hope clarifies the process.
Oh, and Dick (racasey) it's not suitable for broaching in stainless steel..I tried it today.
Cheers for now