Bow Drill – How many things could be ‘just not quite right?’ (The Hearth Board)

In last week’s blog we looked at the detail and considerations in the preparation for the friction fire method of the bow drill. We focused solely on the ground and ember pan, which we found fourteen things to consider. Now let us turn our attention to the hearth board.

Hearth Board:

With the goal in mind to give the customer the best opportunity to create an ember with the bow drill, Hazel (Drill) into Lime (Hearth Board) is one of the most compatible combinations used. There are many other combinations and as your skills develops, there is the choice of trying new things as explored in the blog Friction Fire Experime

Components of the fire bow Image credit Apprentice Bill Burden
  • Dry – A well-seasoned board
  • Not Punky – If sourced as dead standing, the wood should not be decaying or braking up.
  • Thumb nail hard – if your thumb nail can just leave an impression in the wood, then this is dense enough.
  • Not to thin – May break under pressure of the drill or your foot.
  • Not too thick – Powder created on a new board has a long way to fall and cools.
  • Just right thickness – Between fore finger and thumb thick.
  • Squared off – If the leading edge to be notched is squared off forming a 90 degree angle with the top of the board, the resulting notch will be uniform, allowing for greater stability for the ember to form.
  • Drill seat – Set back, centred a drill width from the leading edge maximum needed.
  • Polishing – Gently, using less downward pressure and slower strokes than when going for the ember. The aim of this is to burnish (Polish) the top of the drill and the bearing block to reduce friction in this area when producing an ember.
  • Remove polishing – Polishing will also polish the hearth board and bottom of the drill. This reduces friction resulting in less heat and fuel and must be removed by scraping the surfaces with a sharp knife to remove the shiny surface.
Burning in hearth board and drill
  • Seat the drill – Match the hearth board surface with the drill surface, warm the drill and hearth board, drive off any moisture, not to create lots of dust and wear away the board excessively. This may already of been achieved at polishing, if so complete the above then create the notch.
  • Notch – 1/8 Section, bigger, reduces friction, which reduces heat and powder.
  • Notch – 1/8 Sector, smaller, Powder collects as swarf around edge of drill and not enough into notch to create ember.
  • Notch – Cut out with knife to leave a smooth surface so that the powder is not disturbed when the hearth board is removed.
  • Notch – If using a saw cut shy of 1/8 so that it can be cut smooth with a knife for the same reason in above.
  • Point of the notch too far in – Should be just shy of the centre of the burnt in circle. Too close to the centre, creates a nipple on the end of the drill, and is less efficient.
  • Point of the notch too far away – Too close to the edge, and the powder swarfs and doesn’t collect in the notch efficiently.
  • Underside of notch bevelled – Allows The powder to form a wider stance offering more stable when hearth board is taken away from the ember and in unfavourable conditions.
Varying notch depths with varying results, Image credit Apprentice Bill Burden

That’s eighteen things to consider on the hearth board and thirty-two before we get to the drill, can you add any more?

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