ERC with sinew design

[Kidder]

So I’ve decided to try my hand at a sinew backed ERC bow. I’ve got some very clear ERC boards I intend to use. The intended draw length will be on the longer side - 30 inches, shooting for 50#. First off was hoping someone could suggest a design (stiff handle) to get me started - how long and how wide? Secondly would it be suggested to put a little crown on the back before adding the sinew or leave it dead flat to start? If flat would the sinew need to be applied to provide a slight crown or also kept relatively flat? Thanks everyone!

[WhistlingBadger]

No advice from me yet, Kidder, but I'm interested in the topic too.  With me it's juniper, but they're similar woods.  So, thanks for asking!

[bownarra]

The last sinew backed juniper I made was a stiff handled 58 inch recurve. 28" draw....sinew and juniper are a match made in heaven
the heartwood can take more compression than the sapwood. Definately crown the stave and crown the sinew. A heavy crown is a good thing.

[txdm]

A heavy crown is a good thing.

can you elaborate on why having a heavy crown is good on ERC or Juniper vs de-crowned following the contour? And does that apply to un-backed?

I have plenty of access to 3" juniper branches that would make great bows if I could just peel them and go.

[chasonhayes]

I know nothing and am just starting but I have read several places that ERC needs to be backed. that is probably why decrowning doesn't weaken it. My first attempt to make a bow was from a stave of ERC that I had and it was unbacked and exploded on me. But that means nothing since I have broken all my bows except the most recent one. That is why I switched to hickory. It is supposedly idiot proof but I am firmly testing that concept. After I get some success I would like to try again with ERC. It's really light wood and plentiful around here

[Fox]

A heavy crown is a good thing.

can you elaborate on why having a heavy crown is good on ERC or Juniper vs de-crowned following the contour? And does that apply to un-backed?

I have plenty of access to 3" juniper branches that would make great bows if I could just peel them and go.

Having a heavy crown is a good thing with woods bad in compression and good in tension, now ERC is a wood with horrible tension and not bad compression. This is why you back it, and when backing it with sinew the likelihood of a properly sinewed bow to break in tension is pretty low, where’s its more likely for a erc bow to fail in compression when backed correctly with sinew… that could probably have been explained better and that’s just what I know about it, there’s probably more to it then that though.

[Mo_coon-catcher]

With this combo and crowning essentially comes down to that the ERC is very soft so compresses easily but is very good in its compression resilience so it springs back from being compressed without damage. So because it compresses so easily you need more wood on the belly to resist being compressed and put some strain on the sinew. So you crown the sinew so the wood can make the sinew stretch a little and make use of its snappy nature. If you don’t stress the sinew enough it won’t act much different than any hard backing paired with ERC since a vast majority of the bending stress will be put into compressing the cedar and relying on the resilient nature of the cedar to keep its shape.

Does this make sense? I hoped I worded it well enough to get my thoughts across.

Kyle

[txdm]

Thanks Kyle, that helps. I'm looking for the best design ideas I can use for juniper without sinew. I might use hickory, but most likely will be stuck with preventative backing stuff like paper or linen for the time being.

[Kidder]

With this combo and crowning essentially comes down to that the ERC is very soft so compresses easily but is very good in its compression resilience so it springs back from being compressed without damage. So because it compresses so easily you need more wood on the belly to resist being compressed and put some strain on the sinew. So you crown the sinew so the wood can make the sinew stretch a little and make use of its snappy nature. If you don’t stress the sinew enough it won’t act much different than any hard backing paired with ERC since a vast majority of the bending stress will be put into compressing the cedar and relying on the resilient nature of the cedar to keep its shape.

Does this make sense? I hoped I worded it well enough to get my thoughts across.

Kyle

This is a great explanation - glad you chimed in - especially given your solid track record with ERC (oh no yeah, I’ve been keeping an eye on you!) You essentially mentioned properly or adequately stressing the sinew. That said for a stiff handled bow drawing 30 arrows niches how long would you go tip to tip? Thanks!

[Mo_coon-catcher]

Let’s see, 4” handle, 2” per fade, with flipped tips I think 29” from fade to tip leaving 28” of working limb which should be plenty of working limb but short enough to stress the sinew well. You could bump up to 30” limbs and be good with plenty of reflex induced. So about 66”. I’ve noticed that sinew really likes to pull ERC into a reflex. I had one start to rip apart the belly one time from the sinew pulling such a hard reflex. I think one had 6” of reflex before I started tillering on it.

Kyle