In this tutorial I will show you how to make a fully functioning quite powerful crossbow. this crossbow has the capabilities of shooting sharpened lengths of dowel over 20m. do not point at anyone or use this inappropriately.
Step 1: Shaping the Stock
firstly you must design the outline of the stock used for the main handle of the crossbow. once you have designed the outline, draw it onto the wood and carefully cut around the outside of the line with the jig saw cutter I have used two sheets of 19mm ply (as this was the only material I had available at the time) and screwed them together.
Step 2: Crossbow Prod
the prod is the part at the front of the bow that stores the energy in the timber limbs when the string is pulled back. this is made from a flexible 5mm craft wood that I purchased from the local timber seller. I have cut the strips of wood into 3 different sizes, the cutting list is as follows: 2 @ 500mm 2 @ 350mm 2 @ 200mm the prod is tapered outward so that the smaller lengths are on the inside and the longer lengths are at the back this helps when it comes to storing energy and efficiency of energy transfer to the arrow (bolt). with the stock cut out and shaped I have cut a square hole at the front of the stock which the prod can simply slide through, now pre-drilling a hole through the end of the stock and through the centre of the prod, this allowing us now to drive a screw that will hold the prod in place.
Step 3: Arrow Channel
on the top of the stock I have made a channel for the arrow to fit into and slide across. this depends on the width of the arrow used, I have simply used 10mm dowel that I have cut into 200mm lengths and sharpened. now that you have worked out what projectile width you will be using you can start to make the arrow channel. the arrow channel does two things, it allows the arrow to slide off of the crossbow with accuracy and it also gives you a spot to hook the bow string around so that it stays behind the arrow until you are ready to fire. firstly I have cut one strip of 5mm craft wood to fit on top of the crossbows top edge this running most of the way down the stock (depending on your design) note* previously I have stated that I was using 2 x 15mm thick pieces of ply joined together to form my stock so the width of the piece of craft wood that will sit on top of the stock will have to be 15mmx2= 30mm so now you should have a strip of wood that runs along the the top of the bow. having select arrow width, I have used 10mm dowel, this means that the 30mm strip of wood sitting on top will have 10mm taken up by the width of an arrow, leaving me with 10mm either side, so now I can cut two 9mm strips of 5mm craft wood (allows for 1mm arrow clearance either side) and nail them using small nails to each edge of the top panel that we fixed to the crossbow only moments ago. this will leave you with a 9mm strip of wood, a 12mm gap, and then another 9mm piece of wood, lastly you need to cut a very small price of timber that runs horizontal to two direction in which the arrow is being fired, this piece of also 5mm craft wood, will sit closest to the trigger completing the channel and giving it a U shaped look when looking from directly above, this piece allows for support for when you pull the bow string over it.
Step 4: Trigger and Rope
all that is needed to do now is construct the trigger and attach the rope to the prod. drilling a hole halfway between the width of the timber behind the arrow channel will allow us to slide a bolt through the hole, with the head of the bolt on the underneath side of the stock, we can now slide a washer over the threaded end of the bolt and tighten a nut onto the bolt. ( but not tight, so that when the head of the bolt is pushed it raises the washer higher than the arrow channel so the rope can slide off and launch the arrow.) attaching the rope to the prod: drill a hole in the end of the two 500mm prod lengths and tie a rope or string from one hole to the other, keeping a little slack on the rope so that the wooden prod does not snap.
Step 5: Firing!
to fire the crossbow, pull the rope back over the arrow channel and sit it on-top of the washer, place the arrow in the channel and simply push the head of the bolt up, this will lift up the rope and the energy will be converted from potential energy stored in the prod to kinetic energy transfer to the rope, and then to the arrow.