On teasel hand drill I agree it is a good one. It is my fastest to a coal drill material. On a practical note I find that only the bottom segment will produce a coal, and it only works well if completely dry.
On hearth boards - for hard woods you may need a narrower drill. If a board is too soft or even rotten then you need a much bigger diameter drill.
Someone mention sycamore on sycamore? Boy that sounds tricky. I'd tackle this by hollowing out the tip of the drill so you have a ring.
Richard, London, UK
If at first you don't succeed - pause, reflect, change something and try again.