A double screw vise where the screws look to be fixed to the rear jaw. Also, the legs are attached to the vise, making it a medieval version of the workmate as we know it today. Blockbuch Eysenhuts, 1471. Herzogliche Bibliothek, Xyl III no. 8. Gotha, Germany.
The double screw vise is a piece of equipment for the workbench which saw its first appearance in the late 15th century. At least, that is the date of a woodcut that shows such a device. The double screw vise also appears in later woodworkers books from Randle Holme (1688), Felibien (1667) and Moxon (1678). But apparently there is another medieval image showing what looks like giant double vises - or a mixture of a single screw vise with a parallel guide. I just found this image on Christopher Schwartz blog, and he found it in a book on planes. It seems to be an northern Italian drawing of around 1300. The Italian relation is confirmed by the two-handed plane in use on the first workbench. The screw vise is similarly constructed to that of the vise shown above.
Noah constructing the ark. Northern Italy. Six workbenches with screw vises are shown. In the middle is a stack of lumber with stickers drying, on the right wooden beams are being squared. On the workbenches other carpentry work is done: planing, sawing, using a chalk line, using axes.
A bench and a closer look at the two planes. The large foreplane also has an Italian style grip at one end.
This detail shows clearly the difference between the two sides:
a screw vise on the right, a square stick with pinholes on the left.
The double screw vises of Holme, Moxon, Felibien (E. Crochet ou sergent. F. Estraignoirs. G. Presses de bois [wood press]) and Roubo, respectively. The Estraignoirs superficially look like the screw vise but are used differently as shown in the plate by Roubo below.
The estraignoirs are used with at wedge as clamps for gluing large boards.
Detail of a plate from Roubo. Lart du menuisier (published around 1770).
I liked to make a (Moxon) double screw vise as an addition to my medieval workbench. Good discussions (these and these) on how to make these double vises can be found on Peter Follansbees blog (and in his book How to make a stool from a tree). Furthermore, Roy Underhill has a video show on the subject ("Two screws for you" with Christopher Schwartz) which shows the creation and the versatility of use of the double screw vise. Finally, Christopher Schwartz has a (free) article on how to make such a vise in the popular woodworking magazine. Although the construction is excellently described in the above mentioned sources, there are some details useful to add.
The first issue are the holes to be drilled in the jaws. The centre of the holes of the front and rear jaw have to be at the exact place - this is obvious and can easily be achieved using a jig with fences on the drill press. Less obvious is that the diameter of the holes of the front and rear jaw are different. The rear jaw hole has to be smaller, as the internal thread has to be tapped here (the front jaw is a clean hole and does not have a thread). As the wood threading kits are sold in non metric sizes, I had to work with a 1 inch set. This meant converting the holes to cm drills: 22 mm for the small hole and 25 mm for the large one.
The set-up on the drill press. An mdf board with a long fence is clamped directly to the drill press, as is a short block acting as a second fence. The beech vise jaw is placed against the fence and clamped as well. The Forstner bit can be changed for a smaller or larger bit, while keeping the set-up and centre point at the same place.
The second issue is the bolt/dowel. As they recommend hardwood for the dowels, I used hornbeam. I first made the eight-sided handle and then turned the dowel on an electric lathe to 25 mm thickness. I used a jig to check to exact thickness, made of a drilled 25 mm hole in a piece of wood that was partially cut open. As the dowel needs to go smoothly through a 25 mm hole, but not too smoothly, a bit of sandpaper was held against the turning dowel. The end of the dowel was slightly chamfered.
A jig was used to check the dowel thickness to exact 25 mm.
The third issue is the threadbox (I use a Taiwanese one). It is made up of three parts: the smooth entry hole, the cutter, and the threaded exit hole. This construction means that you cannot go to the end of the handle. This is also not necessary as will be explained later. [But if you wish so, you need to dismantle the threadbox and remove the entry hole (do so after you already have made a start on the thread). The exit hole is then to only way to stabilise the cutting.] The dowel needs to be (good) lubricated with (linseed) oil to ensure a good cutting.
Having cut two handles I found out that they fitted too snug in the threaded hole of the vise jaw. It squeaked on every turn, and oil or wax did not help. Also much force was needed to make the handles turn. I had to redo the threading and set the cutter a bit deeper. This is best done when the threadbox is dismantled. Rethreading the handles did solve the too tight fit and they are working smoothly now.
The dismantled threadbox and the adjustment of the V-cutter.
The handle is held in a workbench vise. At start a slight downward pressure is needed, but later the threading tool guides itself. Once you have started cutting, always use a forward motion. If the cutter binds, back up no more than a quarter of a turn to clear any chips, then continue cutting new threads.
The final issue is where you stop making the tread on the dowel. The front jaw of the double screw vise has an unthreaded hole. This means that the dowel also does not need to be threaded here. I.e. the last 4.5 cm are just blank dowel.
The dowel at the front jaw of the vise does not need to be threaded.
My double screw vise has a length of 66 cm and a height of 10 cm. Each jaw is 4.5 cm thick and made of beech. The centre of the drilled holes are at 13 cm of each end, but placed off-centre at 5.5 cm. The handles of the hornbeam bolt are 10 cm long, the remainder of the dowel 19 cm (so in total a length of 29 cm) of which 14 cm is threaded. My double screw vise can be conveniently attached to my medieval workbench with two holdfasts. The vise works very good and is a really handy tool to have. In fact, I use it more often on my normal (non-medieval) workbench!
The double screw vise in use at castle Hernen.
The double screw vise on top of the bench without any holdfast. Two bench-stop hold the vise in place for planing.
The double screw vise fixed at the edge of the workbench with two holdfasts. Long wooden planks can now be held in place, for instance for sawing or dovetailing.
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