Build Your Own Crossbow

Medieval Design By Leonardo Da Vinci

“Fear is the Mind Killer” This basic precept was the chief inspiration behind Greek and Roman siege weapons.  Leonardo Da Vinci knew this when he created them for the ruling class of his day, as did the Chinese of the three Kingdoms whose comprehensive understanding of mechanics and animatronics was far beyond that of its time.

The benefits of the crossbow weapon as a tool for survival are unprecedented, and can be summed up in one word- invisible.  For the survivalist, Do-it-yourself-er or the urban guerrilla enthusiast it is the weapon of choice- why?  Because its simple design of construction means anyone can build it out of everyday materials without arousing  interest.  The procuring of timber or sheet metal for example, from a hardware store, does not raise the same level of awareness as the purchase of a truckload of fertiliser and diesel fuel.

Medieval Crossbow

Like the hammer, the basic design of the crossbow has not changed- why?  Because, like the hammer, the @#$%*!! thing still works.  The crossbow stock is made up of a center spine covered on each side by a strengthening flank. As a bolted-together unit, this flat-aluminum assembly serves as a combination barrel or chase in crossbow terminology, trigger housing, hand-grip, and shoulder extension.  The bow, or prod, is set into the nose of the fore-stock, and the two-piece trigger mechanism, cut from 1/4″ plate steel, is pinned between the right and left flank pieces just below the receiver. Walnut stock inserts were trimmed and shaped to mate with the stock on either side of the shoulder extension.  Since the string does contact the barrel and is thus subject to friction, we added a pair of shoulder slides to the sides of the chase to reduce string wear and increase bolt velocity. Though these could also be made of walnut, we used Delrin (a Du Pont acetal resin) because it possesses an inherent lubricity.  This crossbow’sopen sights consist simply of a front frame made of aluminum strap, and an alloy rear ring mounted to the receiver. Socket-head cap screws threaded into each of these brackets provide sighting beads, and the rear unit can be lowered or raised as necessary to zero the piece in at a specific range.

Chinese Repeating Crossbow from the Han Dynasty

A repeating crossbow is a type where the separate actions of stringing the bow, placing the bolt and shooting it can be accomplished with a simple one-handed movement while keeping the crossbow stationary. This allows a higher rate of fire than a normal crossbow. More complex ancient designs worked with a chain drive instead: there is a magazine containing a number of bolts on top of the bow, and the mechanism is worked by moving a rectangular lever forward and backward.

The Chinese repeating repeating Chinese crossbowis a device with a simple design. Also known as the lián nǔ meaning “continuous crossbow”, the invention is commonly attributed to the strategist Zhuge Liang (181-234 AD) of the Three Kingdoms period, but those found in Tomb 47 at Qinjiazui, Hubei Province have been dated to the 4th century BC.    Developed by the Office of Strategic Services (OSS) during WWII and tested, but never adopted, by the British Special Operations Executive (SOE). The Little Joe was a hand-held crossbowconstructed of aluminum with a rubber band propelling mechanism. The darts were constructed of wood with a steel broadhead. This crossbow pistol fired the dart at a velocity of 170 ft / sec., or 115.9 mph. Maximum range was said to be 250 yards, with excellent accuracy out to 50 yards. It was intended to be used for eliminating sentries and guard dogs with a minimum amount of noise. The only thing rarer than the darts are the experimental crossbowpistols, with only very few known to have survived.

Crossbow Pistol

For ease of construction, outline the crossbow’smajor parts and drilling point within a grid, this will allow you to make up-scaled templates for the metal pieces. Match the templates perfectly before taping them to the metal and scribing their outline and carefuly cut the aluminum stock, as the pieces must join closely, and ensure the center spine’s weak spot—the trigger guard—is no thinner than 7/32″.

Use a band saw equipped with a metal-cutting blade to trim the parts accurately. Because the smooth operation of the trigger and stringy catch depends in great measure upon the perfect alignment of the three stock component, hold off drilling the flank pieces until you’ve bored the 9/64″ post holes according to the center points indicated on the template. Once those sockets are complete, clamp the aluminum center spine to one of the flanks and recheck the alignment, using the template cutout from the trigger housing. Then drill corresponding holes in the one flank piece

The Modern Twinbow II By Swiss Crossbow Makers

With that done, use No. 6 X 3/4″ machine screws as temporary locating pins for the two bored components, and clamp the second flank piece in place. When you’re satisfied that all three parts are evenly mated, drill the final member. Since the post screws are recessed, you’ll need to countersink the exterior openings with larger bits according to the design of the screws and nuts you’ve chosen.

The steel trigger components have to be thinned by 1/64″ in order to allow them freedom of movement within the stock. Once this is done, those parts can be drilled where indicated with a 1/8″ bit, and the 1/8″ X 3/4″ expansion pin pivots can be pressed in and centered. The pivot pins ride in 9/64″ sockets drilled into the right and left flank pieces; to be on the safe side, you might want to use the trigger-housing template cutout to position those openings accurately.    Both the trigger and the safety catch are returned by small compression springs set into slots cut through the central spine.

Setting the bolt tang or the spring-steel leaf that holds the projectile snug against the barrel, adding the wooden (or Delrin) slides to the flanks, and cutting, shaping, and fastening the walnut inserts that dress the shoulder extension. These can be cut to shape using the template as a guide, then rounded with a sander and bolted or glued to the aluminum spine prior to being finished with varnish or tung oil.

The state of the art PSE-TAC-15- Tactical Military Crossbow

The front sight is a piece of 1/16″ X 5/8″ X 6-1/2″ strap aluminum bent into an open frame configuration so the bolt can pass through it. It’s fastened to the top of the forestock with two No. 6 X 1/4″ machine screws, and a short cap screw locked through its crown serves as a bead. Though we used a machined ring at the rear (to provide a housing for an experimental scope sight), you can make an excellent sighting post by simply drilling and tapping a hole at the top of the receiver to accept a 632 socket-head cap screw about 1-1/2″ in length. This can then be adjusted up or down for sighting.

You need to order a prod with a draw strength of 175 pounds but, if you choose a lighter bow to lengthen string life, you’ll need a cocking lever to pull it into position. You can make one by bending four sections of 1/8″ X 1″ flat metal to create a two-armed, bolt-together yoke that uses mechanical advantage to ease cocking (see illustration). A pair of slots in the stationary part of the lever hook into a 5/16″ X 3″ steel rod fitted into the crossbow’s forestock (this should be located as indicated on the template and pressed in place before you install the prod), and another set of slots cut into the short “jack arms” catch the string. The fulcrum’s just a movable collar that can be locked into the optimal position.

The prod is held in place by a 1/4″ X 1″ X 1-1/4″ block of aluminum faced with a strip of hard rubber. A similar pad, glued to the rear of the prod socket, provides additional cushioning, and the metal block is forced tightly against the bow’s face by a 1/4″ X 1-3/4″ cap screw threaded into a tapped hole at the nose of the stock.    Once the prod’s installed, you’ll have the pleasure of stringing it. Unless you’re extraordinarily muscular, we’d suggest you purchase what’s called a bastard string along with the regular Dacron cable. This set of strands is longer than the service string and thus can be slipped onto the prod more easily. It’s then used to draw the bow’s ears back to the cocked position so the real string can be looped in place. When that’s done, both strings can be released with the trigger and the bastard removed. This is the only situation in which the crossbow should be “dry fired,” since that practice can split the prod.

Wrist mounted, Laser Guided Crossbow

The trend toward Laser technology, miniaturization, mobility and concealment have not escaped the modernisation of the humble crossbow, as the wrist mounted, laser guided mini crossbow by Hobbyist Patrick Priebe attests.  The device’s housing, bow body and bolts are custom built out of aluminum. The bolt rest and trigger string guides are manufactured of Teflon, while steel cable make up the trigger and bow strings. Most of the rest of the parts were turned out of brass and steel, as were the bolt tips.
Although somewhat of a novelty the design in the hands of an experienced manufacturor could be re-engineered into a more serious and permanent piece of hardware, albeit highly dangerous & illegal.


3 thoughts on “Build Your Own Crossbow”

  1. I would like information on the plan’s for the medieval crossbow. If you have them or where I can get the plans. Thanks.


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