free build — shape the arch by hand; it stands or falls by the same line of thrust
The Drawing Board
Build it, then release the load
Set the span, the crown’s rise, the ring’s depth and the number of stones — or grab the brass handles on the springings and crown directly. Drop weights on its back and drag them where you like. The faint gold line is the live thrust; keep it inside the stones. Then release the load.
weights on the backnone
— drag the dark block across the arch to move it —
thrust eccentricity
thrust within the middle third — no tension, the stone is at ease
within the section — it stands, but the stone cracks
thrust has left the stone — this joint hinges