Medieval Crossbow

The subject of this project has been one of my preoccupations since childhood. Growing up in Europe, the local museum had one medieval crossbow on display and I remember looking at it many times trying to figure out how it was made… Of course nobody I talked to had a clue about the actual simple mechanism that is at the heart of the crossbow. Recently, I did quite a bit of research on the matter and came to the realization that although simple devices, pretty much there are no two crossbows alike. This is a rather ancient device, and as the centuries progressed so did crossbow technology. At its heyday in the middle ages around 1300 AD it was used for warfare and hunting, and at the introduction of guns it was far superior being cheap and powerful. This is my rendition of the crossbow, made in the 21st century using old and new materials and techniques.

I made it at the TechShop Chandler for the Dremel Challenge using Dremel tools as well as other implements.

Step 1: Materials Needed

Materials:

Although materials were provided, anybody can build this project for about $10. With a little planning ahead actually it can be made for free as all the materials for all the parts and pieces can be scavenged frequently from the scrap bins.

Ideally some hard wood was used for the Body of the Crossbow sometimes called the “Tiller”. Alternately it can be made of layers of wood or plywood glued together. Some nice designs and figuring can be obtained that way. I used a piece of hard pine that was actually a 2X4 clean, and fairly free of knots or defects. The shape was drawn in SolidWorks and some PDF templates were generated. This simplifies things and people can copy the design more accurately. Besides, the templates can be modified to suit the builder as crossbows were sized and shaped according the intended use and user. Other materials were, one piece of “Bender Board” a strip of MDF ¼ thick and 4” wide sold in 10 foot lengths at home centers, also one piece of PVC pipe ¾ in OD thickness, and about as long as the crossbow. The piece I found was schedule 80 which has twice the wall thickness of regular pipe found in the home centers. Some scraps of tempered Hardboard used for trigger and cam. Arrows or bolts were made from hardwood dowels 7/16 from the craft store. For hardware I used Two 12D sized 3” long bright nails, about 6 small finishing nails, two deck screws 2.5” three drywall screws ½” long and one paper clip. Only the 12D nails are used for the project, the screws and small nails are used for holding, and positioning templates and other the parts during cutting and assembly. One bungee cord slightly shorter than the finished length of the bow, wood glue and finally some stain and varnish of your choice.

Step 2: Tools Needed

Tools:

Since this is a rather primitive device the tools used can be simple also. A successful crossbow can be made out of a simple length of wood with no shaping just some holes… However I used everything I could think of to make this project go faster and precise. Although this write-up seems elaborate, the project can be entirely made in one evening with some preparation. I used the tools from TechShop, Band saw, laser cutter, drum sander, belt sander, thickness planer, jointer, chop saw, scroll saw, drill press, cordless drill, Router table, hand router and an assortment of Dremel tools and attachments for sanding and deburring. Also some hand tools, Philips head screwdriver, various clamps for gluing and positioning, some sand paper, pliers, wire cutters, various files and rasps for shaping wood, template router bit, Forstner bits, and wood drills matching the nails and screws.

Step 3: Begin Work

Fabrication:

Begin by taking the 2x4 to the thickness planer and taking a few light cuts on both wide sides to clean and flatten the wood. Do not take too much it is not necessary as the template will allow marking and cutting of the excess wood. Next take the resulting beam to the jointer and square off the two sides left, again do not take too much.

Next go to the chop saw and cut the wood to the final length of the crossbow plus about two inches on each side for a total of 4 extra inches. You can leave even more if so inclined, it makes for a better support later. You should have two pieces of equal length and some shorter left over piece. Save that wood cut off, it will come in handy later.

Put the two pieces together lengthwise wide side on side, watch the grai for symmetry, and line them up good and clamp them securely. Using the hand cordless drill or drill press, predrill one hole at each end about ¾ or so from the ends, so you can use the two deck screws to hold the two pieces together in alignment for further work… These “sacrificial ends” will be cut of at the end just before staining. From now on, predrill all the holes to prevent wood from splitting, make sure you use undersized drills for screws. Using the Drill press use will ensure that the holes are square to the wood.

Take another slight pass or two on the jointer on what you decide that will be the top of the crossbow to have a flat surface that is continuous without ridges or uneven. You should have two mirror pieces that should always be assembled the same way from now on. Mark them with a pencil so you don’t get confused about the orientation and cut the mortises wrong.

Step 4: Making and Using Templates

Templates:

To speed things up I made templates from thin MDF, sometimes called flexi board. It is very smooth and free of flaws, perfect for templates if you do not require more than 4 inches in width. The PDF template files are uploaded here for everybody to enjoy they are drawn to make use of these sizes. Take a look at the shapes and if you don’t like the shapes modify them to suit. I cut the MDF on the laser cutter but the band saw and drum sander can be used also, if you really want to go medieval you can do it all with hand tools J, however you will be in the shop for a while… You can also cut the templates from some cardboard or whatever appropriate material is at hand…

You can also free hand draw the design of your choice, you cannot go wrong, as crossbows were made in all kinds of sizes and shapes. Only the mechanism principles matter, the rest is just “stile”. Just try to stay symmetric. A search on the internet will reveal hundreds of designs.

Here are some guidelines: The handheld crossbows were held like long guns, so about 30” length is appropriate, they were also no thicker than 3.5”. The Arrows (Bolts) were no longer than 12” and between 7/16 to ½ in thickness. The release cam (called a Nut) was no bigger than 1.5 in diameter and about 1.25 thick, made of horn, bone, iron or very hard wood. The bows were made from wood, wrought iron, or horn and sinew composite, for the ultimate in draw performance. The bow was laced to the Tiller with some various natural fibers or leather or in the case of wrought iron bows, with iron side plates wedges and pins. The bow string was made of some natural fiber twisted and wrapped to resist wear and tear and increase strenght. For finishing the wood surfaces, probably linseed oil, bees wax or similar stuff was used. Sometimes embellishments made from various materials were used for decorative purpose especially on hunting crossbows.

Position templates securely using the guide lines etched on them using the edges and center joint of the stock as registration marks and draw contour lines with a pencil. If you made templates from MDF the tiny holes provided are for some finishing nails used to secure the MDF in place. Look at the lines and See if you like the shapes resulting and modify them if they do not suit your build and stature.

Step 5: Making the Cam Nut

Cam Nut

Release Mechanism:

Using some scrap hard board cut a series of Cam nut profiles on the laser. You might want to mix and match to end up at the right thickness. In this example there are some tiny holes used for alignment pins made of finishing nails. Use them and leave them in place after gluing. Using the dimensions provided, you can make a cam from metal or some Teflon in the lathe if so inclined. Set cam aside to dry in a clamp or vise. When completely dry it is rather hard, dress the part with a file and round off corners, also cut the notch on top with a round file to match the Bolt diameter. Do not make it tight, the bolt needs to let “fly” without friction…

Some non metal Nuts were reinforced inside with a metal pin or wedge perpendicular to the axis to protect from wear from the bolt shaft and trigger release. There is some debate as where the notches for the string and trigger should go, a good rule is that they are cut in line with the center pin. Sometimes the draw string is slightly forward (about 2 degrees) of the center line which makes for a very touchy release. The nut is sitting slightly recessed down from the top surface of the crossbow, just a touch, so the arrow has less friction on takeoff and also will set loose on a straight path being caught by the string squarely on the back of the bolt shaft.

Since you have the two halves marked using templates, you should know with precision where to bore the recesses for the Nut. Using a Forstner bit matching the nut diameter and using the cutoff piece as a side fence (to avoid tear out) drill down carefully about half the Nut thickness. When the two stock halves are joined together and clamped the nut should rotate freely in the recess. Use the depth stop on the drill press to sneak on to the right depth. When done, drill the holes for the pins holding the cam nut and trigger. Back the wood with some scrap so the exit drill hole is not splintered. Before drilling make sure the cam recess is aligned perfectly and not askew. Practice on some scrap if unsure.

While at the drill press drill the two front holes used for the Bow and lashing. It is easier now when the stock is still a square piece of lumber, and the holes resulting are perpendicular.

Step 6: Making the Trigger

Trigger:

While at the laser it is time to cut the trigger mechanism. Use the file provided, and make it from some scrap ¼ tempered hardboard. Laminating two of these together with glue will result in a pretty sturdy trigger. Glue and Clamp and set aside to dry well. Alternately it can be cut from same material using a fret saw.Original triggers were of multiple shapes and mostly made out of wrought iron, some were hard wood. You can bend some cutoff scrap metal to the approximate shape provided, just make sure it pivots properly with the cam and actually fits in the recess cut in the stock for it. The originals were made from 3/8 or thereabouts thick metal.

While the stock is still not shaped it is easier to use the template provided to cut the trigger recess. Screw the pattern down with the small screws in the holes provided. Use a hand router and small pattern bit and a ring spacer in the router plate designed for “Sign Making” That way the bit will run along the edge of the template cutting a perfect recess. I used a ¼ bit and appropriate spacer. You might want to practice a bit to determine the right depth for the bit, as well as direction of feed. The trigger should be free moving but not sloppy, or it will affect the release mechanism geometry. (I did not cut the recess until after shaping but realized it is easier to position, clamp, and way sturdier to cut before the stock is shaped.)

At this stage check the fit and function of the Cam Nut and trigger assembly by using just one half of the tiller and two 12D nails. Simulate tension of the string with your finger, They should move freely without hang-ups. Sand, file and correct any issues now, when assembled the trigger is in place permanently. The trigger needs a spring, to force it down at all times and help in loading the crossbow. I used a large paper clip opened up (see pictures) not too strong but does the job nicely. Alternately a piece of metal from band pallet strapping would be better, but I could not find any laying around. In practice, After firing the crossbow, the cam was rotated in place by hand and the spring would automatically set the trigger tip in the proper place, on the cam nut bearing surface.

Step 7: Cutting Tiller to Shape:

Cutting

Tiller to shape:

Using the band saw prepare to cut along the template drawn lines. Cut the bottom “belly” profile first, this way you can later cut the top profile square on. Use a glue gun to lightly tack the cutoff pieces back on. You can snap them off when done and scrape the excess plastic glue. That way, the top profile can be cut with ease and straight using the flat table of the drill press. Try to stay close to the lines. It will save time and speed sanding and filing. Do not drift inside the line, you can always cut excess but cannot add wood back. Do not cut the end piece blocks by mistake, they are used throughout the build for squaring and holding purposes…

Put the side template back on first half using the same positioning holes, and using a tall router pilot bit take the tiller half to shape gently. Pay attention to the direction of router bit feed and also to the grain of wood, especially at the ends, you do not want to blow out and break a chunk of wood off and ruin the piece… In case of some cheap wood, which I recommend using for practice, I would start over, for hard wood try Super glue to salvage the part. Using the pattern bit saves a lot of filing and sanding work and gives your Tiller a head start. When done with first half attach the second half back on and now the same pattern bit can be used to clean the other surface and use the first half as a bearing surface.

Step 8: Shaping Tiller

Shaping

Tiller:

Using the largest 80 grit coarse drum, mounted in the oscillating spindle sander, sand the sides and bottom to the lines drawn. Do this as a single unit with both halves screwed together at the ends, it is the only way to have symmetry.

By now, the Tiller should be pretty close to the final shape, and resembling a “Queen Ann” cabriole table leg. In fact all this is very good practice for future aspiring period furniture makers J

When happy with the sanding results and all saw marks are gone, take the Tiller to a vice and grasp it using some scrap leather or thick canvas. It will prevent marring from the vise serrated jaws. I actually used a discarded belt from a sander, rummaging through the textile scrap bin turned up nothing good L.

Using rasps or heavy cut bastard files take the stock to the final rounded shape. Sight along the center frequently during filing and maintain symmetry. When happy with the results take out the oscillating Dremel sander and using a progression of sandpapers take it to a nice polished finish. The Dremel takes a lot of sweat and toil from this operation and the shape of the triangular pads allow for fine contouring of the piece. Use a Dremel rotary tool to prepare the flaring for the lashing and bow holes to shape, they are too small in this design to fit files or do it by hand with sandpaper. Use some hand held fine sandpaper to ease any sharp edges left on top and clean any remaining “fuzz”. At this stage the Tiller is ready for final finishing, so treat it carefully and avoid handling with dirty hands or putting dings in the wood.

Step 9: Bow Making:

Bow Making:

This is the part that gives the crossbow its properties and also the name as it crosses the tiller at a 90 degree angle forming a cross. The PVC pipe I ended up with is pretty stiff and makes quite a spring, but it is nothing compared with some of the real bows. Some of the weaker ones made out of wrought iron had a draw strength of 1500 kilograms and going up from there… Some crossbows had to have special devices for drawing the string into firing position. Also because our bow and bungee cord setup is more along the “toy” strength (under 10#) the stirrup found on some crossbows was omitted as it was not necessary. Feel free to add one for looks ;)

Cut the PVC on the chop saw about 3-5 inches shorter than the finished length of the tiller. That will give it the right proportions to the Tiller. Put it on a small wood block and using a heat gun soften it and give it a gentle curve. Make sure you do not get too close and burn it due to impatience… It will soften in a few minutes and be limp like a noddle. Now it can be shaped by hand using some gloves as it is quite hot. Put a chord of about three inches from the bow to the imaginary line of the string. It is mostly for looks, as the bungee does not put any tension on the tube strong enough to make it curve. Work gradually, heat evenly, and do not kink it, or it is ruined. Use a Dremel with a burr and notch the ends to take the wire hooks from the bungee. The bungee should be under some tension while in the bow only so it does not fall out. Adjust the bungee length to achieve that result. The Bow is lashed in place with some parachute cord. See the internet for some fancy weave work to dress up this part.

Step 10: Making the Bolt

Arrow or

Bolt

The proper name is bolt J. Use a nice straight hardwood dowel. Try to get some Hickory if possible, they make nice stiff bolts. Temporarily assemble the crossbow halves with nut, trigger and bow plus string. Arm the crossbow and put a block of wood between the tiller and the trigger. This will prevent from releasing the mechanism as you fit the bolt. Actually there was a safety installed on some crossbows which consisted of a small shaped block of wood attached to the tiller with a string. It was positioned acting as a wedge to prevent premature firing. Put the bolt shaft in the Cam Nut notch and mark a line where it clears the nut. That is usually about ¼ “ or so at that point, this is where the bottom fletching starts. The fletching was made of only two vanes mostly of thin wood for war crossbows (cheap in quantities) and fine feathers arranged as an array of 3 on hunting crossbows. Take the wood shaft to a scroll saw and make a slit about a third of the total length of the bolt. Cut some thin stiff but flexible material (plastic sheet) and make the fletching. Glue the end over the fletching and you have the bolt almost ready. I scavenged a suction cup from a toy bow that fits perfectly on the dowel and hot glued it to the end. Find a suitable solution such as a piece of foam or rubber for the tip. The bolt I made flies about 25 feet with that setup, plenty for a toy.

At this point take a scrap piece of thin plywood about the width of the crossbow at the bow end, and put a notch in it. (see pictures) glue this in a shallow groove cut to take it. The tip of the bolt will rest on this as the tail end is in the notch. This reduces friction and eliminates the need for cutting a channel for the bolt on the top. Some crossbows had this feature some had a channel cut.

Step 11: Final Assembly

Final

Assembly:

Carefully put some wood glue on both halves of the tiller. Make sure you do not get glue on the trigger and inside any of the mortises. Do not put the Cam Nut in, it meant to be taken out for replacement (wearable item) it can be installed easily later. Line up the halves with the two pivot nails left in and the long screws at the ends. The trigger pivot nail can be cut later to size as well as the Cam Nut pivot one. Clamp the whole assembly and let dry well. When dry, make sure any excess glue is scraped off, sanded, and the mechanism is functioning properly. If you glued the whole thing shut, I can only offer advice as where to hang the piece on the wall for decoration J

When fully dry, Cut off the end pieces used for lining up the halves during construction, so it resembles the picture. Sand the ends smooth.

At this point it is time to lash the bow in position using some sturdy twine. I used Parachute cord, for the initial tryouts. It is now all ready to go. Cock the mechanism and do some dry firing to test the can and trigger setup, then load the bolt and point it in a safe direction. Trial fire the newly minted crossbow. You have now gone medieval, well sort of…

Step 12: Finishing

Finishing:

I used a stain and polyurethane to finish the crossbow. That is the reason I do not have a final picture. For some reason it is really slow to dry and I decided to wait a few days before lashing the bow to the end, as I do not want the finish to get marred, and the lashing to embed in the varnish surface. Some crossbows had carvings and decorations all over, they were looking more like a piece of jewelry, than an utilitarian implement. The Metropolitan museum of art in NY has some amazing examples…

Maybe somebody can use the laser or the ShopBot to improve on my design and procedures or maybe even doing some hand carving or whatever… I will post the last picture as soon as the finish is ready to take the lashing

Some parting Thoughts:

I hope You enjoyed this little medieval trip, I did, using the internet and this Instructable for inspiration some pretty nice looking crossbows can be made. I advice that you use a piece of pine instead of some nice hardwood for practice. It is easy to make mistakes. You will feel better if you just wasted a piece of scrap, versus a $30 piece of hardwood. Also the bow can be made to resemble a real medieval bow. In case of a flat blade fitted to the nose the end is cut at an angle as to provide little drag resistance as the string is released. An angle of about 7 degrees is common for a normal length crossbow. When cocked the string should make a perpendicular to the bow as viewed from the side.

Make sure you use common sense when firing this crossbow, do not point at people, animals and other “did I doo that ?!?!?!?!!!!>>>>” items. Although it is sized in strength as a toy and pretty weak by crossbow standards it can do harm if not treated carefully. Also stepping on the crossbow can cause a twisted ankle with dire consequences…Also dropping it on someone head can lead to injury…

My daughter fired it a few times found it very cool and decided that I should make her a small version of it J

Step 13: Shaping Tiller

Shaping

Tiller:

By now, the Tiller should be pretty close to the final shape, and resembling a “Queen Ann” cabriole table leg. In fact all this is very good practice for future aspiring period furniture makers J