Agriculture Reference
In-Depth Information
Figure 85
Moxon's plate 8
showing drawings of the
setting out of a flat and
semi-elliptical arch.
Joseph Moxon
MECHANICK EXERCISES
Or the Doctrine of Handy-Works 1703.
In this respect Moxon (1703, 279) emphasises:
Other kind of Circular Arches, as half Rounds and Scheams [segmental], being
described from one Centre, are fo plain and eafy, that I need fay nothing con-
cerning them.
The first reason for choosing semi-elliptical and straight arches to explain the set-
ting out procedure was the popularity for the semi-ellipse for wide-span entrances
into courtyards; here most horse-drawn vehicles could pass with the driver still in
position as this arch gave maximum height, and thus headroom, within its span.
The straight arch was desired for classical brick façades as a means to securely
bridge an opening yet provide the desired flat beam-like effect.
The second reason for the selection of semi-elliptical and straight arches is the
intricacy of their setting out, establishing individual voussoir positions and their
precise shapes for the cutting templets; vital for accurate gauged work. In the
straight arch individual voussoirs up to the central 'key brick' are unique to
their position; replicated (but only as a mirror-image) on the other half of the
arch. With the semi-elliptical arch, the same factors apply. However, the arch
is geometrically set-out from three separate centres or 'striking points' and so
individual voussoirs relate only to their relative radial point. It is therefore a com-
plicated arch to draw, set-out, cut and 'turn' (build) to ensure an accurate, neat,
and precise arch.
In reading Moxon's description of drawing, setting out, and establishing
the face templets, for gauged arch voussoirs, one needs to be aware of his
