Windsor chairs were designed by turners, for turners. Spring-pole, treadle, and great-wheel lathes were all common in early 19th-century America, along with a few water-driven mills and lathes powered by horses, oxen, and even dogs.
Of the human-powered options, great-wheel lathes had power, speed, and continuous rotation, but the apprentice turning the wheel was an expensive power source – these lathes were best reserved for large-diameter turnings. Treadle lathes had speed and continuous rotation, but lacked power until 19th-century improvements came about. Spring-pole lathes had both power and speed – they were a good choice for turning chair parts. And they are easy to make – my lathe is cobbled together from junk boards, bungee cords, and decking screws, just like they did in 1810.
The lathe was and is the fastest route from a living tree to a smoothly finished furniture part. Long, thin parts are troublesome to turn on a lathe, as they tend to “whip” or bend as they are being turned. Some mid-18th-century Windsor chairs had 30" spindles, but as the need for speed increased, chair backs grew shorter or were divided by horizontal slats interspersed with short, easily turned spindles.
–Elia Bizzarri, excerpt from “For Speed: Fancy Windsor Chair Production in Early America,” in Issue Eleven