Hi. I just started to make 9" letters out of mdf (moisture resistent) board. I am using a templet and a 3hp inverted router to cut 1/2" mdf (MR) BOARD. I am dulling bits in a few letters. I have 3 settings to cut in 3 passes, but I am affraid of getting cut lines on edges if I use the settings. I am cutting with solid carbide 1/4" spiral upcut bits from CR ONSHRUD at over $20.00 a piece. What can I do to get a lot more life out of a bit?