This is a bow I posted recently on the r/bowyer subreddit page. I thought you guys might find it intesteresting, so I'm reposting it here now.
After seing the ingenious overlapping primitive take-down bow introduced over on reddit by u/Mysterious_Spite1005, I got to thinking about how to take advantage of the second benefit of that design: The ability to make a BITH bow "wider" in the handle by stacking bow limbs on top of each other, without compromising the ability to actually shoot an arrow.
To make the most of that idea, I decided, the design would be one that concentrated as much bend as possible near the handle, and which would not otherwise be possible, due to either too much stress or too wide a limb in the center. This way, the friction between limbs would also be minimized. This decision then called for stiff, light outer limbs, so naturally a lever design came to mind.
This is a 60 inch, BITH, reflexed, extreme lever bow. It is rather short, but still manages to have half of its total length devoted to stiff, narrow levers. Thus it has approximately the same length of draw and bending limb, while being only 1 inch wide. It has around 2 inches of reflex, and draws 34 # at 27 inches. It accomplishes this by having three limbs stacked on top of each other near the handle, that move freely against each other. Functionally, the middle half of the bow works as a 3 inch wide pyramidal limb section that straight tapers to 1 inch width right before the lever fades. To keep the limbs aligned, I chose a very straight stave that had a bit of crown, and used a curved scraper to give it a slightly hollow limb cross section. This way the free tips of the "extra" limbs stays in place during the draw.
I was worried noise would be a problem, and thought that friction would steal a lot of energy and make the bow sluggish, but after rough assembly, it only made a slight clacking noise (like an arrow hitting the arrow pass), which i think might have been due to a too loose temporary assembly handle wrap. Nevertheless I glued some felt between the limbs at final assembly which took care of the noise. I didn't do a very neat job of it, and I think a few strategically placed small leather patches might be better.
I just chrono'ed it yesterday, after shooting about a hundred arrows through it the last few weeks. The only appropriately spined arrow I had weighed 442 grains, but it still shot around 160 fps with snap shooting, and around 151 fps with my normal shot cycle (might be a bit shorter draw as well). I think that corresponds to around 169/170 fps with 10GPP. It shoots really smoothly.
Tillering was surprisingly easy, as the circular tiller and limb profiles called for close to uniform thickness. In addition, the three limbs kind of evened out any small irregularities. I did a fairly hurried tillering job on it, as I didn't know if it was even worth the effort, but it was very forgiving. One thing that surprised me, and that you should remember if you want to try this is to make the main limb a bit stiff to start with in the outers, as it doesn't really get any support from the secondary limbs against the "inwards" part of the pull. So if you aren't careful, it will bend too much out there when you go to a short string tillering.
During tillering, I just wrapped a bow string around the handle for temporary assembly.
I might try this approach another time, but then I think I would go for an extremely reflexed r/d design of a similar length. What do you guys think would be a good design for this approach?
Cheers,
Nicolas
Topic: An experimental leaf-spring lever bow (Read 286 times)