Bits-and-braces, similar to drills and augers, work by means of either a “twist” (a single-inclined planed wrapped as a helix around a shaft), or a sharpened “spoon” set at the end of a shaft. The “bit” is the cutting part of the tool, and bits are also part of drills and augers. Spoon bits are much less common today, largely relegated to greenwood traditional Windsor chair makers and period furniture re-creators. Modernly, inclined-plane bits may come in single-helix and double-helix varieties, with additional conveniences such as “spurs” (small, sharp protrusions which score the edge of the circle being bored) and “feed screws” (which increase precision and help pull the bit into the wood).

Spoon bits from the Mästermyr find. Photo from “The Mästermyr Find” by Greta Arwidsson
Four bits from the Coppergate find. Bottom-most bit is a twist bit. Photo from “Craft, Industry and Everyday Life: Finds from Medieval York” by Patrick Ottaway and Nicola Rogers.

The “brace” is the portion of the tool into which the bit is set, and which provides an off-set handle -or crank- by means of which torque (rotational force) may be applied. The brace also has a pivoting head, on which the user may set a free hand or their chest to firmly set the bit against the surface to be bored. Bracing against the chest appears to have been quite common throughout the Middle Ages and into the modern age, as early 20th century examples of chest braces (with specialized heads specifically to be used against the chest) abound. These have the advantage of allowing for greater force to be applied, and freeing up the hand not turning the crank. Braces used against the chest were often used in conjunction with a wooden “bib” to help spread the force across the chest, increasing comfort and decreasing bruising. Braces used by holding the head with the free hand may have been equally common in the Middle Ages, to judge by the frequency of their appearance in art, and continue to be regularly manufactured and used today. Modern braces may also include a ratcheting mechanism and adjustable “jaws” to fit a variety of sizes of bits.

Detail from the Merode altarpiece (circa 1427-32) attributed to the workshop of Robert Campin. Note how St. Joseph uses his chest to press the brace against the board. From the angle he is drilling, I surmise that he is using a spoon bit.
The Dordrecht brace (circa 1350-1421). Photo courtesy of the St. Thomas Guild.

A brace from the Mary Rose wreck (sank 1545) with illustration of bit. Note that the shape of the head suggests use both against the chest and with the free hand.

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