A month into the 2020 COVID stay-at-home order I developed a desire to tap into my neolithic roots, and ordered some supplies to make a longbow. I had picked out a particularly straight 1x2in maple board as a stave at Home Depot the previous year, but didn’t follow through with the arts and crafts portion of the project until the following spring when I had a lot of time on my hands.
I did a little three-point bending test on the stave to see if I could identify the subspecies, but with N=1 I could only really confirm that it was maple. The loading of a longbow when it is drawn is quite nonlinear as a result of the relative beam thickness and high displacement, not to mention the effects of humidity and relaxation on the wood fibers when loaded repeatedly.
There are various rule-of-thumb tables available online, as well as a number of DIY tutorials and forum posts. I looked through a few of these and then made some plans of my own.
After determining the profile of the bow, I took it to rough shape using hand tools, and then removed material from the “belly” (side closest to the operator) until it could flex enough to be fixtured to apply a fiberglass backing with a few inches of “backset”. I made my gluing fixture out of an IKEA bedframe strut. The fiberglass was applied wet with Smooth-On EA-40 Bow Glue and compressed to the stave by tightly wrapping it with bicycle inner tubes. Left to cure for a few days in residential boiler room.
After de-molding the bow and cleaning it up, I began the process of “tillering” - slowly removing material from the belly until the desired draw weight is reached. Spoken in engineering terms: iteratively adjusting the shape functions of two cantilevered (fixed-free) beams until their load-displacement curves are symmetrical and match the desired endpoint in the elastic regime (150N @ 0.75m).
Unfortunately my excitement was my downfall - I was not patient enough with the tillering (once you get close, microns count!) and ended up with a relatively weak, asymmetrical bow. It can still fire, but my neolithic ancestors would not be impressed. Stay posted for Rev B.
