All Hail the King-Post!
Hello again! I hope everyone is staying safe, practicing social distancing, and not going completely stir crazy. While Newlin Grist Mill is temporarily closed due to the COVID-19 Pandemic, we were able to make substantial progress over the past few months on the framing and construction of our new replacement waterbox. Today, I’d like to focus on one part of this, the timber framed king-post trusses which will support the waterbox as it extends above our waterwheel.
What is a “king-post”?
King-posts are a single vertical post, which bear the weight of a structure. In timber framing, these are commonly used to support roofs, or as trusses for bridge construction. This is a 1765 illustration of a king-post roofing truss Labelled “R”, from Francis Price’s The British Architect. 
Here we can see another application of king-post trestle from Diderot’s Encyclopedie, this one is used as part of a floating bridge. 
We are making two king-post trusses (a truss is essentially beams held together tightly in a packaged form, this seems to be a colloquialism within the building trades as the closest period definition I can find is “a bundle”) out of 10”x 10” white oak timbers and with a slightly simpler design (without the struts, or smaller diagonal members coming out from the base of the king-post, these are only necessary with smaller timbers over larger spans). Ours are made up of four timbers, all connected with mortise and tenon joints, each of these joints are then drawbored. Drawboring is the process of boring a hole through both cheeks (sides) of the mortise, then another, slightly offset, on the tenon. When a peg is driven through it pulls the tenon tighter into the joint creating a tighter fit. See the image below for more detail.
Additionally, here’s a 3D model of one of our trusses (they look better in person, trust me).
Once fully assembled these will be about 5’ high by 8’ at the base, and will stand on either side of, and slightly behind, the water wheel. They’ll be connected by a 10”x14” white oak beam about 6’ long, which will support the waterbox. Here’s a graphical representation of both of our trusses and the support beam, I’ll be modelling the rest of the wheel and waterbox over the next few weeks, so stay tuned!
How are they made?
The process started with timber selection, this is one of the most important steps in any project, but is often overlooked. Each piece was inspected for checking, wind, rot, and insect damage. Once suitable stock was found, the base was cut to length.
Then, the center was marked, this became our reference point for all other measurements on the base, that way, even if there are variations in length, the joinery in each will line up.
Next comes the long task of chopping mortises. Using a 2” framing chisel, Tony, along with a number of volunteers, chopped out the center mortise, and roughed in the two diagonal mortises.
As you might have guessed, we now have to cut the king-post’s tenon, this will fit snugly into the mortise, and lock the two pieces together. First, the shoulder is sawed down to the line, then relief cuts are sawed on the cheeks. The waste is chopped away until you have a strong, square, and well-sized tenon.
After a little bit of trimming the joint fits together, and this allows us to start laying out the diagonals. These are laid out by scribing the lines straight off the post and sill, ensuring a perfect fit. From here, the process is pretty much the same, layout, chop, cut, trim, fit, and little by little a structure begins to emerge, along with a very large pile of shavings and chips. Once the two trusses are finished, then we can move on to building the rest of the waterbox. So stay tuned for more updates!
Again, I would normally invite everyone to come visit us in the shop, but it’s currently closed during COVID-19. But I now have a lot more time to write these blog posts, so be sure to check in soon for more!
If you’d like to take the next step and get involved in the shop once this has all calmed, please contact us:
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 PRICE, Francis. The British Carpenter: Or, A Treatise on Carpentry. 5th Edition, United
Kingdom: A. Millar, 1765, Google E-book, Plate F
 "Carpentry – [Plate XXX]." The Encyclopedia of Diderot & d'Alembert Collaborative
Translation Project. Translated by Ann-Marie Thornton. Ann Arbor: Michigan Publishing,University of Michigan Library, 2012.
 Bailey, Nathan. An Universal Etymological English Dictionary. United Kingdom: R. Ware, 1764. Google E-Book “Truss”
Bailey, Nathan. An Universal Etymological English Dictionary .... United Kingdom: R. Ware, 1764. Google E-Book
"Carpentry – [Plates XXVIII-XXX]." The Encyclopedia of Diderot & d'Alembert Collaborative
Translation Project. Translated by Ann-Marie Thornton. Ann Arbor: Michigan Publishing,University of Michigan Library, 2012. http://hdl.handle.net/2027/spo.did2222.0001.414 (accessed March 30, 2020). Originally published as "Charpenterie – [Planches XXVIII-XXX]," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 2 (plates) (Paris, 1763).
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