setting tiller weight goals for mystery wood ......bow finished, pics added

[PlanB]

I've really enjoyed reading this thread. It's been very helpful nd interesting. I'd like to see how your bow works out over time, too Willie, if you post it.

[bow101]

When I hit floor tiller I'm probably 20# to 30# over draw weight(just a guess). By the time I get to low brace I'm about 10# over draw weight. As I remove wood and exercise the bow I slowly draw it to my intended draw weight or just below it and check the draw length. From floor tiller I also just use a scraper and rarely a fine rasp when needed. Taking it slow, exercising the wood and watching for any string follow is the way to go. If your bows are taking excessive set you are either using unseasoned wood or over stressing the wood.

That is a great explanation.  To the point 100%.     Most of us resemble that post nothing more to add.

[joachimM]

  I don't know the qualities of larch at all. I would assume it to be similar to cedar for my experience with it working arrows. For example if I were working a suspect wood I would probably add about 4" the the draw length I used in a mass calculation..

From what I gather in the wood database, Larch, just like douglas fir, is pretty stiff wood (high modulus of elasticity) but not so flexible (you cannot bend it very far before breaking it). Quite the opposite of yew. Relative to its high stiffness, it is rather good at compression though and average in tension.
You can get an idea at the graph in this post: http://www.primitivearcher.com/smf/index.php/topic,50571.msg692410.html#msg692410
you'll find larch at a relative stiffness of 26, and douglas fir at 27.
Compare this to yew or osage, with a relative stiffness of around 15. This means, for the same limb mass and limb thickness, it takes 1.6 times more force to bend the larch than the yew. But the larch will take set or break at a lower draw length than the yew. It's stiffer, but it cannot take as much strain.

That in mind, I think Larch would be better suited for a long pyramid style flatbow than a longbow. To get the most out of stiff not-so-flexible wood, I'd go for thin and long limbs, being less strained. To gain poundage, make'm wider.  Pyramid limbs allow near-circular tiller with even strain along the entire limb.

In principle, for the same bow mass, a larch bow is capable of storing the same amount of energy as a yew bow, but it requires a different design IMO.
Now, with the tillering approach you took, you can make a longbow out of larch. My guess is it will be a bit less deep and a bit wider compared to a yew longbow of the same poundage and length because of the reasons outlined above.   

[willie]

bow101

when one has a weight goal in mind before starting to tiller the stave, the method described by by PatB seems to be as good as it gets. But what do you do with a stave with unknown quantities? If you are tillering to see "just what I can get out of this wood" , (as DC was asking in a recent thread), I would think that one would have to approach tillering from a different direction.

That in mind, I think Larch would be better suited for a long pyramid style flatbow than a longbow.

joachim-

 This bow was en experiment of unknown woods and as a trybow for a future warbow. It gets pulled to 32" and then some. It recovers nicely from just unstrung set and retains about 1" from where the tillering started. It is basically flat for 2/3 of it's overall width, both back and belly. Not really a long bow cross section.