I left this on for about 3 hours and got about 700 steel from a 45% source. Of course this is with surveying IV so I'm pretty good at sampling. Okay here is the macro, its an ingame one

/stand
/sit
/pause 60
/stand
/sample
/pause 120
/macro <macroname here>
What this does is stand up, then sit (to regain action XP quicker.) then waits 1 minute and then stands up and samples for two minutes. Then loops it self and sits and does it all over again.
I'm working on a more efficient one (with about a 7 pause but does only 1 sample per loop)
Which I will post later.