Centring

Centring^[1],centre^[2],centering^[3]^[4],orcenter^[5]is a type offalsework:the temporary structure upon which the stones of anarchorvaultare laid during construction. Until thekeystoneis inserted an arch has no strength and needs the centring to keep thevoussoirsin their correct relative positions. A simple centring without a truss is called acommon centring.^[3]A cross piece connecting centring frames is called a lag or bolst.^[6]

Centring is normally made ofwoodtimbers, a relatively straightforward structure in a simple arch or vault; but with more complex shapes involving double curvature, such as adomeor the bottle-shapedfluein aNorman-period kitchen,clayorsandbound by a weaklime mortarwould be used. Shaping could be done by eye, perhaps with the help of a template, thenstonesorbrickslaid against it. On larger works like a 19th-centurypottery kilnthis was impractical. The structure would be built round a post acting as a datum, and each course of stonework would be set at a distance from the datum.

When the centring is removed (as in "striking the centring" ),^[3]pointing and other finishing continues.

Gallery

A simple arch centre suitable for single skin brickwork.
A centre for a flat segmental arch.
The centring for asemicircular arch.
Centring of trusses, not common centring
Catenary arch kilnunder construction over centring

References

^"Centring" def. 3.Oxford English DictionarySecond Edition on CD-ROM (v. 4.0). Oxford University Press 2009
^"Centre" def. 13.Oxford English DictionarySecond Edition on CD-ROM (v. 4.0). Oxford University Press 2009
^^a ^b ^c"Centering 2, Centring 2" def. 1. Whitney, William Dwight, and Benjamin E. Smith.The Century dictionary and cyclopedia.vol. 2. New York: Century Co., 1901. p. 885.
^Courtenay, Lynn T. (2003). "Centering".Oxford Art Online.Oxford University Press.doi:10.1093/gao/9781884446054.article.t015212.
^"Center 2, Centre 2" def. 1. Whitney, William Dwight, and Benjamin E. Smith.The Century dictionary and cyclopedia.vol. 2. New York: Century Co., 1901. p. 885.
^Ching, Frank (1995).A visual dictionary of architecture.New York: Van Nostrand Reinhold. p. 3.ISBN 0471284513.

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[1] "Centring" def. 3.Oxford English DictionarySecond Edition on CD-ROM (v. 4.0). Oxford University Press 2009

[2] "Centre" def. 13.Oxford English DictionarySecond Edition on CD-ROM (v. 4.0). Oxford University Press 2009

[Century-3] "Centering 2, Centring 2" def. 1. Whitney, William Dwight, and Benjamin E. Smith.The Century dictionary and cyclopedia.vol. 2. New York: Century Co., 1901. p. 885.

[4] Courtenay, Lynn T. (2003). "Centering".Oxford Art Online.Oxford University Press.doi:10.1093/gao/9781884446054.article.t015212.

[5] "Center 2, Centre 2" def. 1. Whitney, William Dwight, and Benjamin E. Smith.The Century dictionary and cyclopedia.vol. 2. New York: Century Co., 1901. p. 885.

[6] Ching, Frank (1995).A visual dictionary of architecture.New York: Van Nostrand Reinhold. p. 3.ISBN 0471284513.

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