On the Flume
Hello again! To continue from the last post, I’ll be discussing the construction of our flume. I had previously referred to this as the "waterbox," but more recent research suggests that “flume” is the period correct term. This is an ongoing project, which we’ve been working on in conjunction with the timber framing and wheel construction thanks to the generous help of both volunteers and school groups. The image below shows one of the sheathing boards which was grooved by students who visited the site, they all signed their work so they’ll become a permanent piece of our mill!
What is a flume?
To begin, let’s define what we’re building. There do not seem to be any clear dictionary entries for the term from our period of interpretation, so I’m unfortunately unable to provide a hard-and-fast definition. But we know flumes existed, and from the few sources which mention them, "flume" seems to be the correct term. The image below shows a flume powering a water wheel from Diderot’s Encyclopédie.
Suffice it to say, the flume is an essential part of the power source for our wheel. Flumes carry water from the millrace to the wheel, and many accelerate the water before reaching the wheel to increase the wheel's effectiveness. Our flume is a large wooden box, approximately 5’ wide by 35’ long, which will be filled with water from our millrace through a cast iron pipe which runs under Cheyney Road. This allows a steady reserve, without having to rely solely on the millrace’s current. The flume sits above our wheel, extending out over the top so that as water is released, it fills the top right quarter of the wheel and causes it to spin. At the end of the flume there is a control gate, which allows us to modulate the amount of water being released, essentially acting like a throttle. All together the flume regulates the water for our wheel, which in turn converts that potential energy into mechanical energy through rotational motion.
What is it made of?
Our flume will be made of two primary components: the sheathing and the framing. The sheathing, which will sit inside the framing, is made from red cypress boards, 3” thick and 10” wide, splined together with white oak.
Once the splines and the cypress swell with water, they’ll create a watertight seal. Around the sheathing there will be a series of timber framed bents (essentially large wooden squares), made out of 8” x 8” white oak beams which will provide rigidity to sheathing, as well as giving them something to press against as the boards swell with water.
These bents will sit on two large 10” x 10” white oak support beams, which will extend out over the wheel and sit atop the king-post truss support we discussed last week.
How is it made?
The first step in making the flume is to prepare the cypress sheathing boards. This starts with jointing both edges square. To joint these long pieces (they range from 12’ to 16’ in length) we’ve come up with a set of specialized sawhorses. These have pegs driven into them, which we secure the boards to with wedges that hold everything tight enough to plane.
Jointing starts with running along the top edge with a coarse fore-plane, then a finer try-plane. Next, a marking gauge scribes the layout line for the spline groove. This is a ¾” square groove, centered on the edge of each board.
A batten is tacked down to the line to act as a guide for a custom grooving plane (made by Jeremiah Wilding) to cut the groove.
Once each board has been grooved, we’ll install the king-post trusses, then begin assembling the bents and support beams. The support beams will be scarfed together out of multiple pieces, following illustrations in Francis Price’s The British Carpenter from 1765. These will extend out from the stone foundation to the king-post trusses.
After these are all in place we’ll begin installing the sheathing, build a control gate, and soon we’ll have a completed flume (it’ll be a lot more difficult than that sounds, I’m sure).
In the coming weeks I’ll be changing the style of these posts slightly, focusing more on the individual tools and techniques of 18th century woodworking and millwrighting, as this will allow me to continue to produce content from home. Once I’m able to return to the millwright shop, I’ll get back to updating you on the progress of the wheel. In the meantime, stay safe, stay home, and be sure to check in every Saturday for the next post!
"Agriculture and rural economy – Sugar plantation and refining." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Ann Arbor: Michigan Publishing, University of Michigan Library, 2010. http://hdl.handle.net/2027/spo.did2222.0001.344 (accessed April 7, 2020). Originally published as "Agriculture et économie rustique – Sucrerie et affinage des sucres," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 1 (plate II) (Paris, 1762).
Price, Francis. The British Carpenter: Or, A Treatise on Carpentry. 5th Edition, United
Kingdom: A. Millar, 1765 Google E-book https://www.google.com/books/edition/The_British_Carpenter_Or_a_Treatise_on_C/sxcbzQEACAAJ?hl=en