Daryl,
I had a little bit of a panic when you raised the issue with the limbs. I took the unbraced picture and placed lines much like your own as a check method.
- Hickory CTP Rekerf - Unbraced - limb length check.jpg (100.36 KiB) Viewed 4130 times
I've measured the working limbs several times - as a necessity for limb thickness comparison - and they measured equal. The picture above shows that, unbraced, they're the same. The two lines are equal length (differing width & colour though). I can only assume it was the bow angle - holding the tillering rope, a phone AND pressing the 'take picture' button can be a challenge at times, especially with a dodgy left leg. I'll be going back to the proverbial drawing board and building a new tillering set up soon. Perhaps with a bolt at 28" to hold the draw there when taking pictures. Certainly with a backboard this time, and perhaps a better seat for the bow handles.
Incidently, I'm in the finishing stages of a light poundage shortbow where I've left one limb 3/4" longer than the other to account for hand placement. It's a prototype of a new design and made from ground laminates, so it will be interesting to see how it turns out.
greybeard wrote:Your bow design is ‘different’, was it based on a particular design or more of an experimental project?
It is a little 'different', for sure. The concept grew from my initial shot at the kerf method (
http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=15852) which stemmed from your own, Colin & Dave's efforts (your own post -
http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=15516 - Colin's -
http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=15843 - and Dave's -
http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=15876). I took Colin's advice in reducing the angle of recurve and lengthening the overall design to 68" ntn. I also included Dave's 'wedged' limb insert and reduced the number of kerfs cut to one from two.
The dimensions on this bow are as follows;
- 68" ntn, 70" total length
- 12" stiff riser section (inc. 4" flat handle and two 4" semi-working fades)
- 12" static tips on both limbs with additional limb depth + wedged kerf inserts for 3" of recurve over this section
- 1.5" width at the fades to 23" from centre (start of kerf) then tapering to 1/2" at tips
Aside from horsebows, I've only shot one static recurve, so my hands-on familiarity with them is rather limited. I seem to often err toward a shorter working limb than strictly necessary, probably due to an affection for horsebows, which you've rightly picked up on. However, to my mind, this is not entirely dissimilar to neolithic bows either - long(ish), narrow (ish) static tips with wide (or wider) working inner-limbs. This bow, once I've ironed out the tiller, will have the entire kerfed section rounded out to reduce mass. This, in effect, won't be dissimilar to neolithic bows - not precisely the same, but conceptually similar. As the limb thickens, it will become rounder, if you get my meaning.
greybeard wrote:I believe that reworking your existing design could produce a more efficient bow
Whether it ends up a 'performance' bow, I'm not overly fussed. It's a chance to try out a technique and prove that CTP (with a Hickory backing) is good for a shorter working limb at mid-range poundages. The previous attempt at this showed that a Red Oak backed Cypress (very) short limb didn't fail in compression - it was the lateral twist that caused longitudinal cracking, although I won't chalk that up as 'proof' until a working bow is finished with that combination. With these timber combinations there is never going to be a 'high performance' bow built, but people don't race Austin Mini's because they're the fastest car about - sometimes it's just about the challenge of getting the best out of a less-than-perfect situation.
With that in mind, I'm still interested in your how you would improve the efficiency of this bow - reduce limb mass + something else? Perhaps changing the width profile on the tips? In future I will undoubtedly be reducing the kerfed, static section but I am hoping that rounding these out on this bow should yield a little better performance, at least.
greybeard wrote:Embarking on projects as yours is about the only way we can develop our bowyer/design skills.
And I'm getting there! Slowly but surely, each build is a new lesson and I've come lightyears from the early builds a year or two ago. It's one thing building a bow from a stave alongside a master, it's a whole other thing to do so from boards and on your own.
Neil