Keep it wet so it doesnt heat up too much, but its not necesary. U can go like full power while cutting the poll, eye and the soft part of the edge. Although, when u get to the tempered edge u have to slow down with the cutting process. This prevents the steel from burning. If you keep the whole axe wet as i mentioned before, go full power with it. I suggest an angle grinder 1600W or more. It is possible to do this job with a cheap 600-900W angle grinder, but it will take like 20-30min.