Overlap the 4 pencils as shown in the picture!
You will also need at least 2 tight rubber bands (I suggest 4 or 5 though.)
Rap the rubber bands around the 4 pencils. Making it look like a T. Tape the 2 pencils right before the erasers and also may want to tape the other 2 at the bottom (this allows for easy handling.)
Cut the rubber bands you have chosen for the "draw string" on the crossbow!
By placing the rubber bands in the pen caps the placing the pen caps over the pencils, it creates a snug fit and requires no tape or glue (this allows for easy changes in the rubber bands, so your crossbow isn't stuck with broken rubber bands on it!)
Tape down an office clip to the end of the main 2 pencils.
Also tape the inside of the clip (where mine is yellow) so it doesn't come up when "cocked."
He it is, thanks for viewing at take a look at my next Instructable "Mini Rocket Launcher!"