Yep, that's the difficult bit. In the end I had to give up using a froe because all our ashes twist in growth for some reason; In a 2m length the grain can twist by as much as 90 degrees. So, I reverted to chain-sawing them in half and, because that was an effort, used the log in the half-round instead of making a plank. Even using wedges and trying to force the split in a straight line didn't work. Luckily, I have plenty of material to work with
However, if your ash is straight grained then an axe and some wedges is probably the easiest solution. I find a froe quite hard work for logs over 8" in diameter.