Negative tiller is not desirable on any design because it forces the arrow into the rest on the power stroke.
When this idea was first published, to my knowledge, it was in the context of a selfbow and I got the impression the ideas were solely those of the author. I commented publicly that I didn’t understand how negative tiller could ever work. Some time after that he and I had a long discussion privately by email, at his invitation, over the course of days or weeks and I thought came to a resolution on the issue of negative tiller, essentially that his ideas were misinterpreted.
My position is this. Tiller is required to offset the asymmetry inherent in having to draw a bow string above the fulcrum of the bow hand. It has the effect of shortening the upper limb, ones string hand simply must grasp higher on the string because you can't shoot an arra through your bow hand. The common workaround is to stiffen the lower limb, which has the effect of shortening it in terms of its spring action. Not surprisingly, simply shortening the length lower limb has exactly the same effect even if the spring strength is made constant with the upper, i.e. no more or less positive tiller. So, the logical conclusion is that shorter lower and stiffer lower (positive tiller) are interchangeable. They have the same effect and can be used in any combination.
We find this in practice, with all current production bows and countless examples from antiquity. Not surprisingly, shorter upper and negative tiller are not well represented in either category. The published scientific study of the bow and arrow supports the positive tiller paradigm, predominantly Kooi as related by Tapley.
http://www.goarchers.org.uk/mechanics/ My experience with seflbowyering over the last 10 years or so supports this position as well. In general, when I shorten a lower limb I can use less positive tiller and still get good arrow flight with modest nock point setting and a balanced (in terms of stresses upon the limbs) bow.
I don’t think the author of this idea ever intended to propose bows be made with shorter upper limbs and negative tiller. Rather the opposite, that bows be made with longer upper as an alternative to weaker upper. Makes a heck of a lot of sense actually, why make the upper weaker and thus more strained when you could just as easily use shorter lower? Why use imbalanced spring action when you can use geometry instead, or in combination with less imbalanced spring action? He simply wanted to counter the modern renaissance idea of a “symmetrical” bow, where arrow pass is placed 2” above dimensional center, is desirable or well balanced. When in fact this design exaggerates unnecessarily the inherent asymmetry cited above.
My purpose here is not to debate this question. I’ve resolved the issue for myself, completely. My purpose is only to present another perspective, the accepted dogma for millennia actually, for those who may follow. I think its incumbent upon me. I have a large personal investment in the craft. It’s been very good to me personally. Others have invested a great deal of time and energy and materials even, very generously, helping me to understand and use the underlying physics and principles and to be a better bowyer, to promote the craft. So I’m happy to help those who follow in my footsteps, obliged to even. Misinformation or misinterpreted information does nothing but harm. But it’s a task I honestly do not relish because more than likely some or most who disagree will see me as the antagonist, malicious even. They already have said so.
Topic: Tiller top limb (Read 869 times)
