This is a Heavy Hunting or War crossbow, as very thoroughly documented in "The Crossbow, Medieval and Modern Military and Sporting" Sir Ralph Payne-Gallwey, BE. This type of bow was used widely throughout western Europe from 1370-1490 and there are many similar bows depicted in art and various Museums; Doge's Palace- Florence, Musee' d'arme, Paris.
Materials: Beech, Oak, Steel, brass, Hemp Rope, Modern Bowstring
Tools: Metal Lathe, Mill, Grinders, Belt Sander, Various saws, Torch
The intent of the project was to make a bow as much like an authentic one as possible. The book contained detailed measurements and diagrams, which was extremely helpful in the patterning aspects. Whether Sir Ralph took these dimensions off an original is not certain, but the one diagrammed in the book looks very much like the ones in museums, so it seems highly plausible that he did so. In any case, such a detailed set of illustrations is hard to pass up when you don't have an original available to work from.
The Prod (bow), trigger, and part of the crank piece of the windlass were traded with François L'Archevêque (non-SCA), who started making a bow several years ago, but did not complete it.
There was little attempt to use period processes for the metal components in this build. All parts were made for this project, except the trigger spring. For a majority of the newly-fabricated steel components, the initial shapes were traced into a CAD program and cut with a water-jet machine. the forward pulley assembly was welded together and all components were then ground and finished on a combination of belt-sander, die grinder, dremel tool, and extensive hand-filing. Obviously, only the hand-filing is a period process. The pulleys on the windlass assembly underwent an additional step of being turned on a metal lathe and case-hardened with a case-hardening compound and an oxy-acetylene torch. Case hardening was done in-period, and these were considered critical-strength components.
The screws for the lock assembly were also lathe-turned from stock material, to match those in the illustrations. Thread size and pitch was undefined in the documents, so a us-standard 1/4-24 pitch was used.
The pulleys were assembled into their mounts and the axles piened and made flush. The windlass was assembled with 8mm hemp rope, with the anchor point on the crank section sliced into an eye and whipped.
The Beech stock was cut on a bandsaw and the round area for mounting the nut-holder was drilled on a drill press with a forstner bit. The trigger side-plates were inlet with a small router and the edges refined with a set of small wood chisels to get a tight fit. The trigger mounting inletting in the stock was cut with a mortising machine and a 1/2" mortising chisel. The stock was then coated in several applications of natural boiled linseed oil, drying and buffing between coats.
The brass inlay on the bolt-channel on top of the stock was milled and the matching slot for it was likewise milled on the same machine. Tolerances were easily controlled this way and fit was extremely tight.
The bow was assembled, several times, to adjust fit and was finally mounted into a vice to pull it back using a steel cocking cable made for bending the bow for stringing it. The objective pull of the bow was 1,000 pounds. And then things got interesting. The handle was cranked and the bow came back, significantly stiffer than expected, resulting in the rope on the windlass breaking. Calculations regarding how hard the crank had been pulled indicated the bow had far exceeded expectations, pulling 2", less than a quarter of the designed 9" draw distance, and the tension at that point exceeding 1,500 pounds. This would indicate a final pull of over 5,000 pounds. A jig was then fabricated to hold the bare prod and cable, and a load measuring device was attached. Several iterations of grinding the prod and pulling it on the jig have brought the pull down significantly - to somewhere around 2,000 pounds, so more thinning is underway.
"The Crossbow, Medieval and Modern Military and Sporting" Sir Ralph Payne-Gallwey, BE.
Doge's Palace, Florence
Musee' d'arme, Paris