It's near the core of the wood. In order to minimize the impact of the strikes, it's important to keep the chisels sharp. I sharpened them frequently when I was carving zelkova wood. I am sharpening them just as often as I did then, perhaps even more frequently this time.

木材の芯に近い部分です。叩く衝撃をなるべく抑えるために、鑿たちを鋭く研いでおくことが重要です。欅材を彫っていたときには頻繁に研いでいました。そのときと同じくらいに、ひょっとしたら今回はさらに頻繁に研いでいるかもしれません。