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The U-shaped part is a kind of crankshaft. It gives the brace much greater torque than other kinds of hand drill; a brace can be used to drill much wider, and deeper, holes than can a gear-driven hand drill. The price of the greater torque is lower rotational speed; it is easy for a hand drill to achieve a rotational speed of several hundred revolutions per minute, but it requires considerable effort to achieve even 100 rpm with a brace. Due to the design of the brace it tends to be easier than a power drill to keep at a precise 90 degree angle.
The front part of the brace consists of a chuck spindle with V-shaped brackets or clamps inside. Turning the spindle of the chuck in a clockwise direction tightens the drill bit in the chuck and turning in a counter-clockwise direction loosens the bit for removal.
In most braces, immediately behind the chuck is a three position gear release which allows ratcheting of the handle when in tight spots. Turning the gear release from the center position allows ratcheting the brace in the direction needed. Turning the gear release fully clockwise lets it remove wood in a clockwise direction with the ratchet action going counter-clockwise. Placing the gear release fully counter-clockwise then allows turning the brace and bit in a counter-clockwise direction, usually to remove the drill bit from the hole. The center position of the gear release prohibits the ratcheting effect.
The U-shaped crank has a wooden spindle on it and, along with the top spindle, is allowed to freely turn under the hands without producing wear and tear on the hands (thus, no blisters).
- White, Jr. 1962, p. 112
- White, Jr., Lynn (1962), Medieval Technology and Social Change, Oxford: At the Clarendon Press