Yew specific gravity, performance and MoE

[NicAzana]

I was lucky enough to get a load of freshly cut European Yew staves this summer from a family member, and spent the last three days drying a sample in the oven at 105 *C (221 *F).
It is all from the same tree, which came from a stand of fairly large diameter (10-30 inches?) straight-growing yew in a timber forest on sandy soil here in Denmark.

It turned out to weigh 79.9 g and I just measured its volume to between 100-105 ml by submersion in a measuring cylinder with 10 ml markings.
That gives me a specific gravity of .77-.78 which I think is pretty good for Yew, especially low elevation yew. Even if I make a conservative estimate and assume that it wasn't completely dry - say, 79g (even though it only lost about 0.2 g in the last ~6 hours of drying), and take the absolute maximum volume (105), that still gives me an SG of .75.

My question is, does anyone have any specific advice for yew, when it comes to adjusting for density, beyond the general observation that higher density allows for a more narrow and/or short design?

And does anyone have any concrete information on how modulus of elasticity changes with specific gravity in yew? I've recently started using VirtualBow in the design phase (and a bit for informing tiller shape), and MoE is a key input.

Thanks,
Nicolas

[superdav95]

I am sure the man on here that might know this is Del.  He has a you tube channel that has a lot of info too with yew.  As for my anecdotal experiences with pacific yew.  Has been that it varies from stave to stave and tree to tree.  I’m sure this would be the same or similar with European yew.  Ring count for me is a bigger factor for yew.  The better bows I’ve made from yew have been those with higher ring count.  This is true for variety of bow builds.  I’m not saying that a decent cannot be made with yew with lower ring count but it’s my opinion that higher ring count is better.  Yew is magical stuff and quite different then really anything out there and hard to compare it with other woods.  It’s basically a natural composite.  The tension strong sap wood side and compression strong heartwood side.  Congratulations on your wood score.  You will have some good bows come from it and be surprised at how soft it is to work.  It’s softer but also springy wood.  Very cool stuff. 

[mmattockx]

And does anyone have any concrete information on how modulus of elasticity changes with specific gravity in yew? I've recently started using VirtualBow in the design phase (and a bit for informing tiller shape), and MoE is a key input.

Instead of trying to use some general rule of thumb on MoE you are better off measuring it directly with the wood you will actually be using. It isn't too hard to make a test rig that will get you much better data than information from someone else taken from a different piece of wood.


Mark

[willie]

I will second Marks advice about making a simple bend test.

Consider also that the Moe input in Virtualbow does nothing more than help you predict theoretical draw weight of your design at some arbitrary stress. Determining a pratical working stress for your materiel is more difficult and will take some trial and error.

Can your yew stash can provide some smaller samples that can be utilized to make some minibows that can be reverse modeled in virtualbow with the goal of fleshing out a suitable working stress?

[Hamish]

It depends on what style of bow and its purpose, draw weight, to what suggestions could be offered.
You don't really have a problem with yew. Even the poorer specimens make a lovely bow if designed and made properly.

Yes, Del will chime in soon with some good advice.

[Del the cat]

IMO the only generalisation you can make about Yew is that you can't make generalisations!
I used to use simulation programs and computer stuff when I designed electronics, and its all well and good.
But for making bows, is it "primitive"?
I was going to post my latest flight bow (boo backed yew) but the plywood riser is held together with screws, so I decided it was not primitive enough.
If we use the mass principal (and I don't so maybe I've got the wrong end of the stick) doesn't that pretty much account for density ring count etc?
Anyhow, the properties of a stave can vary along its length (even across its width!), and surely that's the challenge of working with wood?
It all seems a bit of overthink to me... after all, you can only use the wood you have! it's no good pining for some perfect piece that is half way round the world with extortionate shipping.
Maybe I'm just a jaded old git?
I'm not "anti" using the software, just beware its limitations, and its not for me.
Del