lasermen,
If this is for mild steel give this a try, use between 15 and 125 Hz for your frequency (start at 125 Hz and work your way down), use between 25 and 15 for your duty cycle. Set your gas (O2) at about 900 mbar; start your feed rate at 2000 mm/min and use between 12 to 20% power. If it is not deep enough slow the feed down or adjust some of these parameters. You may end up with some slag that covers the top of your engraving; this should be easy enough to remove.
Balance is the key to good deep engraving.
Hope this helps,
chadxyz