Bow drill, bigger = better

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DocBurN

Joined
Feb 25, 2010
Messages
403
Ron Hood recommanded a thumb sized drill for the bow drill friction fire..
Wouldn't a bigger drill create more friction on the board and be better?

Feel free to give me your input.
Thank you
 
Bigger would mean more surface area, but it would also mean less rotation, which is more important(along with downforce), so in this case bigger doesn't necessarily mean better. Feel free to apply this philosophy in other areas of your life if it makes you feel better. :)


Gautier
 
With a larger drill, the tip will be exerting less psi and will be spinning slower which will create less friction and heat. The thumb rule is a compromise between drill size and strength (any thinner and you will snap the drill).
 
My thumb isn't all that large - so I think about a thumb in a half (for my body size - I am 6'5") is ideal. I think if you have the size or muscle and can easily spin a drill of an inch or two - do so.

If you can't - pick a smaller spindle.

http://www.youtube.com/watch?v=94XYwGToVwY

Check out that video - Ray Mears tends to use, what looks like, HUGE spindles. But I think he gets a lot of heat out of the surface area. He is, however, 6 foot tall and is a brawny lad. He can likely get a lot of speed generated by his method.

Same with the female in this video. I think her form and method is so good she can get away with a slightly larger spindle:

http://www.youtube.com/watch?v=PlxujVPiN6U



TF
 
That second vid helped me a great deal in getting better with my bow drill technique.. :thumbup:

I've tried thumb size and thinner, within reason and was able to get a coal.. you just have to get the feel for your spindle when drill on how much pressure you wanna put on it..

Best of luck to you..
 
More area for friction just makes you work harder to heat the larger area up as much as the smaller area with a small spindle.

Since you are not an infinite source of usable power, you will instead spin a large spindle slower, exerting the same amount of effort, and not getting the contact surface as hot.

Ideally, if you can shrink the width of the spindle without compromising it's strength or your ability to easily spin it, you should do so. You'll get a coal with less energy exerted.
 
Thats is exactly what happen.. wasted a lot of energy last time.. and to make it more challenging there had been an heavy rain the day before and everything was damp..

Problem #1, im not sure what is the best wood for the drill and board (that is available in the Quebec, Canada's forest.. usually try to pick up "something" dry.. the bow is made of green off course.

Problem #2, I rush too much when i think i got it.. then when i need to restart bowing and im tired. That is fixable with a few tips from the second video posted here, thanks man.

I get smoke everytime, but the coal is something else, only when im lucky to get it before getting tired. Last time after 30 min, i decided to switch for a bigger drill to get that "more friction area" .. now i'll aim at small drill and more rotation
 
What about something like this:D

PMOC000_0185hugebowdrill-small.jpg



Found it HERE
 
DocBurN said:
Wouldn't a bigger drill create more friction on the board and be better?
Click to expand...

The friction force depends of 2 factors: The coefficient of friction (depends of the material) and the normal force (how hard you push down).

I like smaller spindle that will spin more, but a bigger one might support a higher push.

I started writing a small paper on Bow-drill from a engineering POV, I really should finish it.
 
I try to keep it to a little over an inch diameter, but I have definately used thicker. I pay more attention to length of the drill, as I find it easier to bare down on a longer drill. 8"-12"
I also prefer a longer bow, as it conserves energy.
 
I generally go with the thumb rule, but also found that different things work with different woods. A thinner drill on harder wood lets you increase speed. A fat drill on a softwood like basswood works great as well. When I have to carve down I usually make it about thumb size thickess or slightly larger.

I also like making long drills, about 12-15" so I'm not hunkering down so much when drilling. More of a comfort thing than performance.
 
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