Hickory backed ERC questions

[Woody roberts]

I’ve started working on my hickory slats and a ERC stave. Unless you all change my mind this will be a pyramid style.
64” ttt, 2” wide at the fades. Thinking the hickory needs to be about 3/16” thick and the cedar 7/16” with 3 or 4 inches of reflex at glue up.
Looking for 45/50 lb at 26” draw

Thoughts, criticism, ideas, recommendations all welcomed.

[RyanY]

Sounds like a lot of reflex to me. I’d make the backing thinner and make the belly lam thicker. ERC is elastic in compression and will likely be thicker than what you’d expect from other woods. I also think 2” wide pyramid bows are narrow in most woods but I’m the only one.   

[Kidder]

I’d second Ryan’s advice on going thinner on the backing and that you’ll likely need thicker for the belly.  If it were me I would consider substantially trapping the back as well. I probably also wouldn’t exceed 3 inches Perry reflex - my only experience with more than that (boo/erc) ended with a fretted belly the entire length of one limb.

[Flntknp17]

Agree with the two above.  I have experimented quite a bit with hickory slats as backing the last couple years, and I would really advise something like 1/8" for the hickory on something soft like ERC.  ERC can certainly take the compression if laid out right and tillered well, but I do believe the bow will live longer and be less prone to hinges and inhomogeneities in the ERC the thinner the hickory is.  I use 3" of Perry reflex on hickory or osage bellies, but have had better luck with 2" or so when using maple or other softer woods.

Matt

[Woody roberts]

Thanks guys, this is the kind of info I was hoping for.

[bownarra]

Less reflex. 2" is plenty.
Hickory thickness doesn't matter as long as you don't run out of belly. 3/16" is fine. The work of the backing is done by the outer couple mm of thickness. Unless you go down to veneer thicknesses thinning it doesn't make any difference. Narrowing it or crowning it are another matter and these two things will reduce the stretch resistance of the hickory. I really don't know where this thinning the hickory thing came from but it doesn't hold up. Reucing the thickness of the backing from say 1/4" to 1/8th does nothing to change the properties of that outer bit of hickory that is doing the work. It's like saying only use a 1/8th piece of hickory but change the core wood and the belly will act differently.....

[Eric Krewson]

I have only made one hickory backed ERC bow, my hickory was 1/8" thick, the backing looked good with no runouts.

The bow surprised me, very light in hand, it really zipped an arrow but the hickory failed in short order. I have had several hickory back bows meet the same demise, perhaps my hickory isn't as good as it looked.

I have a bow making friend who has made a ton of bamboo backed ERC bows with no problems, his bows are fairly narrow, I am guessing 1 3/8" or close to it. If I make another backed ERC bow it will be bamboo backed.

Here is my bow in the building process and the failure.

Glue up, my ERC is flawless, no knots, twisty grain or runouts.



Only moderate reflex


Looking good at brace



BOOM!

[mmattockx]

Reucing the thickness of the backing from say 1/4" to 1/8th does nothing to change the properties of that outer bit of hickory that is doing the work.

No, but it does change the neutral axis of the limb and how much strain the belly wood will see because of the significant difference in the stiffnesses of the two woods. A thicker backing will shift the neutral axis towards the back, adding extra strain to the belly. A thinner backing reduces that effect.


Mark

[txdm]

I did a 60"x2" ERC/hickory a while back and used roughly 1/8" hickory backing. I mis-tillered it an didn't hit the draw weight. After some piking and heat treating it ended up being a very quick and light 28lb bow. I remember putting 3" of reflex on glue up and it retains 1" of reflex after my poor tillering and several hundred shots. Such a beautiful wood combo, and a good performer if done right.

[Stoner]

Been there, done that. I feel your pain, I have built some all wood lams. Got them shooting, but have yet to get them to finish stage. John