9/14/25: my last diagram is not quite right. I will update it.
The curvy Italianate molding above that window in the center? How did they do that?
How did carpenters in south eastern Massachusetts in c.1850 lay out the picturesque pediment so it could be cut and assembled?
This was the question posed to me by Nathan Goodwin of H.I.S. Construction. He was asked to lay out a copy of that molding for installation above two garage doors.
Nathan and I posted ideas back and forth. Nathan needed to draw and define the curves, especially how the arc over the shuttered windows evolves into the arc which ends in a point above the main window.
While we focused on that curve I wondered how the master builder laid out the whole design. What geometry might he have used so that the pediment complimented/completed the windows? So it is integral, not just stuck on the top?
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A center window flanked by 2 skinny windows, now shuttered. Together with their casings they form a rectangle. The 3 windows' tops are half circles. Around and above them is the embracing molding which follows the semi-circles before it swoops up with a reverse curve to meet at the center in a point. The molding seems to be the same width throughout.
We saw that the pediment was derived from the windows. The windows and their casings were a rectangle, 4 units wide. Note the red rectangle and lines below the window sill.
The curve for the section of the pediment over the side windows was easy to see and draw. It's the extension of the small windows' half circles. The red dashed line and the dotted lines drawn here radiate from the center of those shuttered windows. I shared this with Nathan.
The pediment's height over the center window was also easy to find - see the dashed red arc on the right. The half circle's radius is half the width of the windows. Note the black dashed line. It's a reverse curve. Where was its center? How was it generated?
The white-out on the image comes from us exploring and rejecting options.
Nathan and I shared ideas back and forth. He posted this suggestion: a layout based on the width divided into 4 units.
He extended my 4 units into rectangles, divided the rectangles themselves into 4 parts and used 3 units as the radius for the molding hoods over the shuttered windows.
The sides of the rectangles cross the semi-circle. He added diagonals from that point to the center of the top of the main window. The crossing point became the center of several exploratory circles for the reverse arc curving to the pediment's center.
Nathan ended up with this diagram. It worked for the width of the garage doors; he could lay out the curves and cut the parts.
I wanted to know about the original design - the layout of windows, casings, pediment with moldings. How might the master builder/ joiner/carver (I don't know his title) have laid out the design?
Here's what I saw. Nathan's division of parts worked across the width of the window. The whole width is 16 parts/units.The center window is 6 parts wide; the casing on each side is 1 part. The side windows are 3 parts wide; with one part on each side for the casing.
Nathan's geometry for the reverse arc over the main window also worked. The radius of the center window's arched top is 3 parts, with the casing: 4. This doubled is the diameter of the circle which draws the arc of the pediment.
