My cheap crossbow broke, so I decided to make a wooden one using the left over parts (limb, trigger mechanism and foot stirrup) that could fire marbles or ball bearings by having a top barrel so the bearing doesn't jump out.this is my first instructable and im also writing this in hindsight; meaning i've already made it. this is more of a guide to the layout not strict instructionWARNINGIf you plan on making one of these you should treat it as a normal crossbow. NEVER POINT IT AT ANOTHER PERSON OR LIVING THING!I made this for target practice and for fun but a ball bearing could be potentially lethal! obviously bear in mind that power tool and hand tools can cause harm so work safe! I take no responsability for any damage or injury sustained by making and using one of these!
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So first of all you'll need some wood, I used sapele because I had some but you could use most hardwoods (bear in mind it will be under a lot of stress from the bow being in tension and then released so go for something sturdy like ash or beech if you can) the stock needs to include the distance the bowstring is drawn back, a handle or grip and the butt which is normally the lenght of your forearm.
Step 2: Layout
really the only critical part of this project is routing the channel for the marble so that it sits right and can roll freely while still leaving room for the bowstring. That and the recess for the trigger mechanism. in my case i had 16mm bearings and the string was 6mm thick so i made the depth of both channels 5mm with a 45 degree bevel on the inside.
Step 3: Shaping!
using a spokeshave i rounded the edges and also cut a notch for the bow that i packed with leather to hold it steady.
Step 4: Changes/improvements
I planed the stock down to about 30mm thick, routed an ovolo to reduce friction on the string and made a longer barrel to hopefully increase accuracy.