Sunday, November 04, 2007

The following is from Joe Barry, woodworker, occupational health therapist, sometimes teacher and writer:
Ever wonder why screws and doorknobs turn clockwise? In a right handed world it uses the strongest muscles. To supinate (turn the hand palm up - think of holding a bowl of soup) or pronate (palm down - think of the prone or front leaning rest position for doing push-ups) there are muscles in the forearm. However, the primary supinator is the larger bicep! Which means that supination is the more powerful movement for a righty. To apply power for pronation with the right you will notice you begin to recruit the musculature of the shoulder - which is what a lefty has to do with tightening screws. In industrial health it is a well established fact that leftys have a greater incidence of injury and repetitive strain disorders.

There is a tendency to ambidexterity in my family. My father and grandfather were ambidextrous and two of my three brothers are as well as I am. I can tell you that it is more of a curse than blessing. When I was a kid I didn't know what hand to catch with so the ball usually bounced off my forehead. If I managed to catch the ball in the glove I would throw both ball and glove to 1st base! When I started teaching I had to learn to be careful how I demonstrated because as the grain changed under the plane I would swap hands leaving the kids to wonder just what it was that I had done.
Joe, this is fascinating, and made more interesting if you take time to observe your own hands, arms and shoulders in motion. This same kind of thing seems to apply to the motions of the mocotaugan, or one-handed draw knife. By observing the motions of the arm in use of the knife, you note that as the the tool is pulled toward you, the amount of strength available in the arm increases, whereas in using a traditional knife cut, away from the body, available cutting strength is reduced as the arm reaches full extension. Joe adds the following:
Another biomechanic principle is in action using the mocotaugan, a drawknife and a sloyd knife as taught by Willi Sundquist is that the elbows are pulled into the body providing a brake on the motion so that you don't commit seppuko (hara-kiri, literally belly cutting, is considered a rude expression by the Japanese). You can use the larger muscles of the back such as the latissimus dorsi to take really large cuts with a regular drawknife and still exercise considerable control and safety despite the initial misgivings you may have on seeing this for the first time.

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