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A Combat Crossbow

History

The crossbow owes its beginnings to the Manuballista of the Roman Empire, which was a hand held siege weapon derived from the Greeks Gastraphetes that was a form of light artillery. Like many Roman things which were lost during the dark ages, so too was the crossbow, it doesn't reappear for use in warfare until the 10th or 11th century, but it isn't until the beginning of the 13th century that it becomes a favored weapon in the armies of the day. At this time the crossbow undergoes significant changes possibly related to experience gained in the first crusade and becomes larger and longer with prods of horn and sinew and now uses stirrups to enable these much more powerful crossbows to be drawn.

At the end of the 13th century we saw the introduction of the Anglo-Welsh longbow with draws of 100-180 lbs these bows quickly proved their supremacy as in the hands of an expert they could shoot up to 20 shots per minute. The best longbows made of Central European mountain-grown yew could produce greater power and range than most military crossbows of the 14th century. Although the draw weights of the typical longbow was half that of its contemporary crossbow, it produced a power-stroke that was three times as long. Add to that the fact that the typical 300 lb crossbow could be fired perhaps 4 or five times in a minute, and that it was far more expensive to construct, one can see why longbow-men were preferred.

So why didn't the longbow replace the crossbow completely? Because of the time it took to "grow" a longbowman. They had to be strong, well-fed and well trained, typically from childhood as it took ten to fifteen years to train a good longbowman. The crossbow on the other hand is much simpler to use and train, and is well suited for use by the citizen soldiers of medieval armies (assuming you have the money). In addition, due to their expense one could justify retaining them locked-up in a military armory and not out amongst the peasantry for constant training (as with longbows), a good thing when you are worried about a revolt!

In response to the longbow, crossbow makers began making heavier and more powerful crossbows using first belt-hooks to draw them, then inventing new lever devices such as the Wippe, Goatsfoot or Gaffle and finally a Windlass or Cranequin system. Around the middle of the 14th century we see the introduction of steel prods, and though they were less efficient than horn, they were cheaper, less sensitive to weather, and low maintenance. The draw of these new military bows were around 1000 lbs and could hurl a 3 ounce bolt up to 350 yards. Even larger siege bows had draws of 2000 lbs and ranges of 450 yards with 4 or 5 ounce bolts!


Design

Crossbow Design

In designing this crossbow, I chose the more basic Western European design that features a narrow, more angular stock and a simple trigger shape and roller-nut release. Western European bows commonly had a metal-side plate that was used to reinforce their narrower stocks next to the nut-socket. For simplicity of construction I chose the most extreme of these mechanisms which features a nut socket which is completely bored out and which uses only the side plate to hold in the nut.1

The style of the stock is approximately 15th century Italian and is based upon a design provided by the makers of the steel prod I used. Payne-Gallwey uses a similar stock design in his book but with a more complicated lock mechanism.

In order to hold a SCA combat bolt, I had a choice between using a completely non-period plastic tube as many people currently use, or use a relatively rare period mechanism called a spring clip. I chose an oversized spring clip mounted over the lock which would put pressure on a bolt slid up underneath it. The spring clip is the most unsightly part of the crossbow, but in my opinion less so than a plastic tube. As this was to be an SCA combat crossbow, I knew that too many flourishes would be wasted on the stresses of combat, and so the design of the bow was to remain simple and undecorated. I wanted a bow that would stand up to the rigors of combat, and having seen a number of light-weight pine-wood SCA crossbows, I decided that a more period hardwood was still called for, I knew that this would make holding the crossbow for extended periods more difficult, but I also figured that the extra heft would act as a stabilizer for the shots.


Materials & Construction

When constructing a custom crossbow, the place to start is with the prod. In order to fashion a period bow, I decided to use a steel prod, and finding one was perhaps the most difficult part of this entire process. Eventually however, I did find a supplier through the World-Wide-Web(WWW). Alchem Incorporated.2 produces custom steel prods which are perfect for reenactment, and which is what I started with for this project. I chose the 75 lb prod because it would comply with all possible reenactment uses and is specified at 600 inch/pounds of draw (75 lbs at 8" draw) which is well within all society rules. Just getting the prod from Alchem was not enough however, it seems that Alchem doesn't know the proper length of the string to use with their prod, and it took further research to find someone who had actually used their prods and determine a proper custom string length: 27 1/2 inches! Now I had to find someone who could produce a proper crossbow string of that length.3 The reason I chose modern materials for a bowstring is twofold, first is cost and time, researching period string making was proving to be a near impossible task, and one which relied heavily on the skill of the string maker in identifying and using the proper materials. Second was to reduce the risks associated with breakage, a broken string snapping into someone's face could be hazardous!

Now, this prod as I mentioned has a 8" maximum draw from a 3 1/2" brace (the distance of the strung string from the prod when at rest) which results in a release point that should be 11 1/2" from the groove. This is the most critical measurement in the design of the stock to allow for maximum use of the energy in the prod. I constructed the stock from 1" x 4" red oak planks, available at local hardware and lumber supply stores which I cut with a scroll saw. By using thin lumber like this, there was no need to split the lumber to hollow out the space for the trigger mechanism, I simply routed out the space for the trigger bar (3/8" mild steel bar stock) in both plates using a router. In period this would of course be done using a chisel to create a mortise, but this technique allows me (an amateur woodworker) to achieve the high degree of precision needed in making a crossbow. I clamped together the two boards and used a drill press to bore a smooth nut socket through the entire stock.

Lets talk about the nut for a moment. Period nuts were made of wood, horn or metal. Metal nuts were slow and wood nuts had a tendency to split. The best nuts were made of horn, but the precision carving and shaping to produce a horn nut was well beyond my capabilities. After a bit of research I found a reference to using Delrin, a modern plastic to use as a substitute for horn. After a bit of shopping I found a source4 for 1 1/2" Delrin rods which would be perfect for creating the nut for the crossbow. I cut the proper length of delrin using a handheld miter saw (produces a much finer cut than power tools) and then used the scroll saw to shape the finger into the nut (see picture). Finally I had to create a sear, which is the hard metal plate or pin used to seat the metal trigger. I did this by cutting a notch into the nut opposite the finger and gluing a plate of 16 gauge steel into the notch. I then carved out the nut where the trigger would rest so that the end of the trigger could slide into place against the sear.

Crossbow Nut

Now I carefully sanded and smoothed both the nut and the socket until they fit tightly, but operated smoothly. Next I drilled the pin hole for the trigger, and used it to mark the trigger which I also drilled for the pin. Note: when marking the trigger, always leave the trigger a bit long. You can used a grinder to grind down the tip of the trigger to make it fit, but if you have cut the trigger to short to reach the sear, it will still be too short no matter how many times you cut it! I then fit both the trigger and nut in place and made the fine adjustments to get smooth operation of the lock mechanisms.

Once the lock was working correctly, I glued both halves of the stock together and mounted the trigger with a brass pin. Now the nut was locked in using the brass side plates and brass screws. Next I shaped the stock by sanding it to smooth the hard edges, but not too much, as the western style was very angular. I strongly rounded the butt to allow for stomach braced drawing of the bow.

Finally I fitted the prod to the stock, the angle of the groove must be carefully measured and tested to ensure that the string rests against the stock, but only lightly. After temporarily binding the prod to the stock, I test fired the bow several times to ensure proper operation and then remounted the prod using the period technique of using wet rawhide lacing which when it dries makes a permanent mounting of the prod. Obviously there is much more that can be done when fashioning a crossbow, and further work begs issues of finishing touches, fine tuning, maintenance, performance enhancements, etc. But this will suffice for describing how this piece was constructed.


Summary

After all is said and done, I very much enjoyed making this crossbow and intend to make several more, using what I learned to make them better. The next effort will probably use a stronger prod, and I will use bow irons and a stirrup to make mounting the prod and drawing the bow easier. I would also like to create a fully authentic sport bow with a 175 lb draw and exotic woods designed to fire real bolts for use in competition shooting.


Bibilography


Footnotes

1: Payne-Gallwey, pg 99 fig 56.

2: Alchem Incorporated, 314 East 195th St. Euclid, Ohio 44119, (216) 313-8674, (http://www.alcheminc.com/crossbow.html).

3: JB Strings, Jim Branch (520) 887-5556

4: Cadillac Plastic, (520) 741-1900