Bit Replacement

You will usually start getting rougher surfaces at first where the bit cuts at the bottom of your cuts and then over the whole cutting area, you will have more fuzzy textured surfaces since the bit is beginning to tear at the wood instead of cutting cleanly. I usually start to see wear occurring after about 10 carves (most of mine are in the 8-12 inch square or round range) and by the time you have done about 20 you will really start to see the fuzzy surfaces.

I think that I'm getting about 15 cuts to a bit, mine are not as cut intensive as Bob's since I tend to do more recessed wording for signs than his intricate cuts. I've also found that you can extend the bit a few more cuts if your willing to do a little hand "sanding". I use a kitchen scouring pad and run it over the piece, it tends to remove the fuzzy's quickly and without marking up the wood.

I usually see the first signs of wear or fuzzy's on the side where the bit is lifting upwards, so to the left side of your piece as you face the machine bed. I'm guessing that this is because you don't have the downward force helping the bit cut, you're pulling away from the wood (obviously ever so slightly) instead.