Medieval carpentry didn't vary all that much from carpentry today except for the fact that they didn't have electricity hence, no power tools. Well, o.k they did have the waterwheel and a few things like that, but bottom line most everything was done using human power and lots of it.
The medieval carpenter's tool chest would have been quite recognizable to modern eyes. They had their hammers, mallets, saws of various sorts, chisels, drills, knives, snap strings, axes, adzes, measuring instruments, planes and the occasional specialty tool. Each tool had one or more tasks that it was intended to perform and was designed to accomplish those tasks in the best manner that experience and medieval technology could provide.
|The "bow saw" was basically two upright sticks with a stretcher bar between them. The blade was inserted either between two spindles at the bottom of the saw (in the case of a the "turning saw" variant of the bow saw) or simply pinned into some slots cut into the bottom of the uprights. A heavy cord that was twisted at the top of the two uprights tensioned the saw. The cord was kept from untwisting by means of a short stick (sometimes referred to in later periods as a "bird") that served as a handle for twisting the cord and as a stop to keep the cord from unwinding. The entire mechanism is an exercise in "tension and compression". The mortise and tenon joint by which the stretcher is kept in place in the uprights forms a fulcrum so that as the cord is twisted it compresses the upper end of the uprights, it forces the lower ends apart. The blade being pined in one form or another is then put under tension by the leverage of the bottom ends of the uprights. The more the cord is twisted... the greater the tension the blade is under. Very simple... very elegant...|
Making the Saw: (This ain't tough... stay with me here...)
The Blade: The only part of a bow saw that may not be readily available in the size form that you might want it in would be the blade. While there are places where you can find blades for saws such as these... probably the easiest way to obtain a blade for your saw is to simply make one. This isn't as difficult as you might think. Go to a good hardware store and look up bandsaw blades. I would recommend going with a 3/8" (.375") width blade to start with if you're making a turning saw... If you plan on making a fixed blade bow saw for heavier duty cutting you might wish to buy a blade of at least ¾" (.75") width or more.
Once you have these blades (which come in a variety of teeth per inch (TPI) and some other characteristics, you can cut from it a piece of whatever length you want your saw blade to be and drill holes of appropriate diameters in the blades to facilitate fastening them to your saw. The nice thing about this manner of obtaining blades is that you can get a number of "spares" out of a bandsaw blade... nice to have when you're miles away from a blacksmith! The Frame: As noted above, the frame of a bow saw basically consists of three sticks of wood... and there are no "hard and fast" rules in determining the size or exact shape of those pieces. Generally speaking, the heavier the work you have planned for your saw the heavier you want the construction of the saw. The saw should fit comfortably in your hands and should be comfortable to work with... neither too large where it might become unwieldy to use or too small where it will be insufficient to the work.
The picture below describes the dimensions that I used to build my turning saw and is presented as a suggestion for how to layout and assemble the frame of the saw. Just follow the basic pattern and make any adjustments you think would make your saw better for your use...
Odds and Ends: I used a heavy twine (about 5 loops of it... but .25" sisal works better) to make the cord used for tensioning. Just put your blade on the blade end and start wrapping cord on the cord end. Tie the ends of the cord together, insert the bird an twist... if the cord or anything else breaks, you've cranked it up way too tight.
Oh... I used some basic brass pins to hold the blade in the handles. It can be bought at various hardware stores easily enough... nails also work well too, just remember to file down the edges where you cut them.
Like the saw itself, the bird isn't really anything more than a heavy stick used to twist the cord. On my saw its about 7.5" long by 3/4" wide by a bit over 1/2" thick. As with the cord ends of the uprights, I took a rasp and worked the end where the cord wraps around to a: hold the cord in place better and b: relieve any sharp edges...
... and again... "Have fun... Make stuff..."