Tools of the Trade: The Double-Screw
As we’ve progressed through the tools of the trade series, we’ve covered sharpening and preparing our tools for work, laying out what we want to make, and finally holding our work with a holdfast. Today we’ll add another tool to the list: The double-screw.
What is a Double-Screw?
Unlike holdfasts, Moxon doesn’t provide us with a very thorough explanation of the double-screw, but Randle Holme, author of The Academy of Armory, does: “they are made of Spar, the Screws are fitted with holes or Screw Boxes in the Spars fit to receive them, which being turned, the two pieces are drawn together so hard, that they hold firmly any thing set between them.”
Let’s unpack this description briefly. First, in this context, “spar” means a piece of wood 2 inches thick by 4 inches wide. What Holme is describing is a vise with two threaded wooden screws and two wooden blocks, which can be used to hold your workpiece. That’s simple enough, and luckily, Holme, Moxon, André Félibien (a French contemporary to Moxon), and Denis Diderot all provide us with illustrations of this or similar tools.
Below is Randle Holme’s illustration of a double-screw. You can clearly see the threads on the screws that tie into the rear block; as they’re tightened they press down on the front block, creating a clamp.
Here’s Moxon’s illustration of a workbench. On the right-hand side, there are two wooden pegs sticking out of two wooden blocks attached to the bench. While there’s debate as to whether or not a double-screw would actually be attached to a bench in this manner, it at least provides us with more examples of the style of double-screw in use at the time.
This plate, from André Félibien’s Des principes de l'architecture, de la sculpture, de la peinture, et des autres arts qui en dépendent, shows a very oversized double-screw on the wall behind the bench. Notice its similarity in style to Moxon and Holme.
And finally, Diderot, in his Encyclopedie, shows a dedicated double-screw bench. This time two nuts are twisted down on threaded rods in order to provide clamping pressure--as opposed to Holme, Moxon, and Félibien where the rods act more like bolts--and have a shoulder which clamps down on the outer block, and in turn, the workpiece.
How are they used?
Now that we have a better idea of what these are, let’s take a look at their use. As we mentioned earlier, this is all Moxon had to say on their use: “its farther Cheek is laid an edge upon the flat of the Bench, and fastened with an hold-fast, or, sometimes, two[,] on the Bench.” This gives us one major piece of information: the double-screw is held to the bench with a holdfast, to allow a joyner to keep a piece steady while being worked.
Here are the ways in which we use our double-screw:
Clamping on the edge of the bench to hold your work on end
Clamping on top of the bench to hold your work on edge
We even use it while truing the edges of our rim boards, as our volunteers Mark and Michael demonstrate here:
To 18th century woodworkers, double-screws were a vital part of the workbench tool kit, and they’re still useful for us today. Join us again next week, as we continue the tools of the trade series with a look into planes.
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 Moxon, Joseph. Mechanick Exercises: Or, The Doctrine of Handy-works. London: D. Midwinter and T. Leigh, 1703. Page 65, Google E-Book, accessed April 13, 2020.
 Holme, Randle, The Academy of Armory, Chester, 1688. Ann Arbor: Text Creation Partnership, 2011. Page 354, Accessed May 5, 2020.
 Holme, Randle, The Academy of Armory, Chester, 1688, plate 142.
Moxon, Joseph. Mechanick Exercises, page 69.
 Félibien, André, and Adriaan Schoonebeek, Des principes de l'architecture, Digitized copy, Page 135. Accessed May 5, 2020 https://archive.org/details/desprincipesdela00feli
 Diderot, Denis. "Cabinet making and marquetry." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. (accessed May 5, 2020) Originally published as "Ebenisterie-marqueterie," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 4, Plate IX. (Paris, 1765).
 Moxon, Joseph. Mechanick Exercises, page 65.
Diderot, Denis. "Cabinet making and marquetry." The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project. Translated by Ann-Marie Thornton. Ann Arbor: Michigan Publishing, University of Michigan Library, 2010. http://hdl.handle.net/2027/spo.did2222.0001.442 (accessed May 5, 2020) Originally published as "Ebenisterie-marqueterie," Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, vol. 4, Plate IX. (Paris, 1765).
Félibien, André, and Adriaan Schoonebeek, Des principes de l'architecture, de la sculpture, de la peinture, et des autres arts qui en dépendent: avec un dictionnaire des termes propres à chacun de ces arts. A Paris: Chez la veuve & Jean Baptiste Coignard fils, 1699. Digitized copy, Accessed May 5, 2020 https://archive.org/details/desprincipesdela00feli
Holme, Randle, The Academy of Armory, Chester, 1688
Holme, Randle, The Academy of Armory, Chester, 1688, Ann Arbor: Text Creation Partnership, 2011, Accessed May 5, 2020 http://name.umdl.umich.edu/A44230.0001.001
Moxon, Joseph. Mechanick Exercises: Or, The Doctrine of Handy-works. London: D. Midwinter and T. Leigh, 1703. Google E-Book, Accessed May 5, 2020, https://books.google.com/books?id=t_IRCzjTf08C&newbks=1&newbks_redir=0&dq=Joseph+Moxon&source=gbs_navlinks_s