Thoughts on using spinny bits encased in a hollow chisel on wet or wet-ish wood:
1. Start at the end of your laid-out mortise in the direction that the clearance hole on the chisel points. i.e., if it points left, start at the left end. The means you will be ejecting waste toward the already-cut side, which is a definite plus.
2. The first plunge will be difficult. Go very very slowly, and only nibble a bit before raising the chisel to allow the chips to clear.
3. Work your way down until the depth stop engages. Watch it carefully, though, as the leverage of the arm can overpower it and you’ll find yourself cutting deeper and deeper.
4. Use overlapping cuts, you’ll get cleaner results that way.
5. The wet wood (oak in this case) will clog easily. Take small bites and raise to clear often.
6. You will likely have to cut slightly deeper than you expect, as the projecting auger doesn’t make a very flat bottom. The overlapping will help with that, too.
7. Clean out the mortise of hot, sopping wet wood with each pass. What’s that? Uh-uh, I’m going to pretend you didn’t say that.
8. Get yourself one of the conical diamond sharpeners for the end of the hollow chisel and use it periodically.
9. Get a piece of beeswax (I pick ’em up at the hardware store) and rub it on both the auger and the faces of the hollow chisel from time to time.
10. Stay inside the lines, you can clean up the walls with a sharp chisel easily enough.
