This is the fanlight over the main door to the Old First Church, built in 1803-5 in Bennington, Vermont. Lavius Fillmore was the Master Builder; Oliver Abel, his Master Carpenter, and Asa Hyde, the Joiner and carver.
The fanlight design consists of 2 parts: the 'scallops' around the curve and the 'leaves' coming up from the base. It is simple, graceful.
How was it laid out? In 2012 - when I first wrote about this fanlight - I knew the geometry for the scallops around the curve - expanded daisy wheels on the horizontal and the vertical axis.
The 3 leaves below the scallops? I was lost.
Laurie Smith - English timber framer, historian, geometer, the most knowledgeable person I know about the use of circle geometry in medieval design and construction - provided the answer.
Here is our geometry for the fan light. It may not be how Lavius Fillmore laid out the pattern.
The circle, its 6 points around the circumference laid out by the radius of the circle, is set on a line which defines the shape of the fan light.
The circle is surrounded by 6 circles which have their centers on the 6 points. The center pattern is a daisy wheel with 'petals'.
The circles expanded.
This set of circles around the original circle adds petals
to the exterior of the first circle. Add the fanlight shape and the petals become scallops around the arc of the fanlight.
Rotate the circles 15* - or 1/2 a petal - and the fanlight's scallops' locations change.
Overlapped, the daisy petals create the double scallops of the fanlight.
The overlapped petals are also the pattern of the 'leaves' in the fanlight: too big, not in the right location, but crossed as are the leaves.
Add regulating lines from the center of the circles to the second ring of circles and center lines in the petals.
Connect the center points of the scallops to each other. Where they cross the petals is the center of the small circles which form the leaves.
The radius of the circles is the distance from the center of the petal to the scallop.
I've drawn it in red to make it more visible. It is a complex layout for a seemly quiet, unassuming design.
This pattern was drawn at about 3/8" = 1'-0". A scale of 1"=1'0" might have been easier. However it would still be tiny here on the page. For clarity I left out the overlapping scallops.
The real fanlight was laid out full scale - 5+ feet across - on a framing table or floor. The proposed design sketch would have been studied, the arcs drawn with a compass using chalk or charcoal, the lines checked, redrawn, the points pinned. Finally, when the regulating lines were erased, the simple, clean design was visible.
I would like to have been there, listening, watching. I think they were pleased.
Thank you, Laurie, for your help.
my drawing in 2012