fire drill query

[RAPPLEBY2000]

Hi just a proffessional question here,

i've been teaching bushcraft for a year or two now and never really thought to ask, when clients are using the bow drill sometimes the baseboard/drill get polished and therefore ineffective i know how to fix it, but what causes it?

i'm thinking not enough downward pressure.

what do you think?

 

[torjusg]

I am not at all good at fire by friction, so my opinion isn't neccesarily to be taken too seriously.

You are probably onto something with the insufficient pressure thing. It most commonly happens to me when I use too soft materials that crumble under too much pressure and then harden to a glaze. But I have also experienced it with too hard woods with too little pressure. And I believe that the problem is more frequent when two factors are involved:

Dampness: Makes the fibres softer and alignes them in the spinning direction, thereby reducing friction.

Flexible woods: Flexible woods (especially with fine fibres) seems to work poorer than brittle woods. My guess is that the flexible woods bend and align in the spinning direction, while fibres in brittle woods break and becomes dust for the pile.

Torjus Gaaren

 

[RAPPLEBY2000]

i was teaching someone today and the materials used were:

bone dry poplar baseboard

bone dry hazel drill

flint bearing block

standard bow set up

the chap i was teaching did not have the right technique by a long way, lot's of drill wobbling, very short bow strokes.(too much ego too little care )

 

[Ogri the trog]

I thought it was as follows - even if it is not, its a good story....
The tip of the drill and the hearth get hot whilst drilling - that we know 'coz we get fire in the end.
All woods carry a certain amount of resin, which becomes more fluid as the temerature rises and just like jumping on the sand near the surf, comes to the surface of the wood.
The temperature continues to rise and the hot dust created both absorbs and help to evaporate off, the volatile solvents in that resin.
Once the volatile content has deen driven off, you are left with what is in effect a laquered, polished surface in the bottom of the drilling hole.
The reason, I believe, that insufficient downward pressure often gets this result is because the abrasive qualities of the hot dust do not cut through the glaze before that glaze sets hard enough to resist the increasing efforts of the driller to get the ember established.

ATB

Ogri the trog

 

[rich59]

It is certainly associated with hard wood base boards. I'd go with the resin/ lacquer idea.

 

[RAPPLEBY2000]

nice theory, i think i may go with that one,
(i'll have to dumb it down first though!)

 

[BobFromHolland]

My bearing block (which is probably bankirai) looks like glass after frequent use and lubrication with fresh leaves.

Lack of temp and surplus of moisture??

Bob