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Interesting HLD bow explosion (Pic heavy)

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BoltBows:
Hi there folks!

With a lot of inspiration from Leon (aka Leonwood) and Simon (Simson) I wanted to build a HLD elderberry bow. Leon gave me a great piece of elderberry to use and so it began.
I did try to make an elderberry HLD recurve before, but after heat treatment it failed and developed fatal crystals in the sides near the handle.
The first HLD I tried to make involved a lot of work with gouges and scrapers to get the hollowed out shape. Being a woodworker I decided that could go a hell of a lot quicker!
So I took up one of my granddad's old concave moulding planes. (Not sure what this one is called in English.) And well to put it shit way: It will save you a lot of time ;)

So this HLD elderberry made it to a 28'' tiller when I decided to shorten it a little to get a few lbs extra. It was just under 40 and I wanted about 42-44.
The left limb seems to do way less than the right, but the left limb had quite a kink which resulted in reflex exactly where the knot it, in the middle of the limb!
Quite dodgy, but amazingly it did what it had to.


However, after shortening it, it exploded spectacularly on full draw. So now the interesting part:
It was the right limb that broke, although in the whole process I felt like the left one was gonna go.
And what's more interesting than that, is the way it broke. As you can see on the picture below it split lengthwise for almost half the limb.
It looks very much like the backing of the limb has been broken off because of the limb deformation, although it might have been that little knot you can see in the picture on the left.
however I still think that knot was not the case, because of the fact that the limb halves almost split a cm apart in width.
In my mind this confirms the theorie of the cross section tension which makes this HLD so fast, however this was probably a bit too extreme.

After this happened I wondered what the cross sections looked like exactly, so yeah.. here they are:

Looks pretty good I suppose. I even compared them to Simson's recommendations which are in his tutorial on his website, and I was damn close!
Keeping in mind that he makes even more extreme versions of this, mine should be okay I guess.
So yeah, I probably went a bit too extreme, wanting too much from this piece of wood. But it resulted in an interesting project I think!

Cheers guys, thanks for reading.

Jaap

Badger:
  I don't believe it has ever been confirmed that the hollow limb is a fast design. Have you seen any tests done on it?

leonwood:
Hey Jaap, nice to see you posting here! Sorry to see this one explode, thought you made it! The hld cross section looks pretty good to me.
However it also could have been the wood since my broken elderberry from last week and Erics from last month where from the same tree and they all broke!

leonwood:

--- Quote from: Badger on November 19, 2018, 07:30:25 am ---  I don't believe it has ever been confirmed that the hollow limb is a fast design. Have you seen any tests done on it?

--- End quote ---

Don't believe anyone has ever done any comparison tests, I know for sure my fastest selfbow is a HLD black locust recurve but I am not sure if that has anything to do with the HLD part.

Would be interesting to test it though... Take two staves from the same tree an tiller them at the exact draw weight and mass, one hld and one flat. Would that work???

Bayou Ben:
There you have it....if Leon's bow broke from this wood, it's the wood's fault!

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