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I have created a bow-drill for the purpose of starting fires.

The wooden shaft's diameter is about the diameter of a typical male thumb, and is approximately 11 inches in length.

The bow string is standard nylon string.

I know that it is typical for the string to travel up and down the drill shaft as the bow oscillates, however, almost without fail, my bow string travels up more than it does down and eventually works its way off the drill shaft.

How do I reduce the bow-string travel that results in detachment from the drill shaft?

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migrated from diy.stackexchange.com Sep 28 '12 at 7:56

This question came from our site for contractors and serious DIYers.

2 Answers 2

The answer is in your bowing action - the travel comes from your arm movement not being in a straight line each direction: there is a bias one way or the other. Usually the bias is in the direction that relieves the string overlap, in your case this is up the way, so you need to actively bias the other way slightly. I find it is easier to bias against an up-tending bow than a down-tending.

The way I learned to do it without much travel was by using the same process as playing snooker or pool: learning to move my hand in a straight line along the length of the bow/cue by involving my entire arm correctly.

On the push stroke try to push downwards with the heel of your palm - almost grinding the bow downwards - and on the return stroke just keep the bow level.

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Wrap the string around the shaft in the opposite direction. Then it will tend to go down, but your uneven pushing and pulling will counteract it. If that doesn't work, try cutting a slot in the shaft and putting a keeper (such as a star washer) on it.

You can also try this.

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I tried the keeper idea, but the string wants to move up or down with such force that it overlaps itself to the point that the friction becomes too great to keep moving the bow –  George W Bush Sep 28 '12 at 7:14

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