Bow backing advice?

[Grooveski]

Been roughly roughing out a yew log. Got it dry, only 49" long with a crack right along one face. There's still a bow in it but it's got fourteen knots as yet with only maybe four left to hack out.

The bow's for my mum if it works out, looking for 35lb at 23"(ish) and would rather it didn't blow(or at least blew safely) so I'm going to back it.

Don't know whether to chase a ring as best I can then back with rawhide or decrown?
I've got sinew or bamboo(or glass fibre - boo and hiss all you want, it's for my mammy, pain is not an option) that I could use if I decrowned but it will be pretty horrific underneath.
Not sure if sinew would handle it.

The rings are quite tight. I doubt my ability/patience to follow one as my first attempt at yew.

 

[Snufkin]

Yew is pretty forgiving stuff. Chasing a ring is not so vital with yew (though I would try to keep it as close as possible) a few violations are OK. It looks like you have a pretty high ring count there, I'd take the sapwood down to a quarter of an inch and then back with rawhide (or FG is you are really worried) and go for it. Your target draw weight sould be OK. If you're going to sinew it I'd remove all the sapwood as I've read of the shrinking sinew tearing off the sapwood.

 

[Grooveski]

Started working it down. It's maybe not as bad as I thought. Two of the problem branches are smack-dab in the middle of the fades and the other bad one is central at least.

Interesting about sinew tearing off the sapwood, hadn't heard that one before.

Ok, going to aim for using hide unless I make a mess in which case I'll square it off into the heartwood and stick on a strip of bamboo.

Amazed how soft and easy to work the yew is.

 

[Toddy]

Can you explain why the Yew needs to be backed, and why the materials you have mentioned are best suited, please?
I'm not being awkward, I'm just curious.
atb,
mary

 

[Grooveski]

Yew doesn't need to be backed, leaving on sapwood acts as a natural backing.

This log is a knotty piece of work though and I'm a rank amateur so there's a fair chance of it breaking. Putting a backing on is a safety precaution so that if it does go the backing will hold the pieces together and hopefully stop them flying apart.

If it goes during tillering fair enough. It's only muggins that gets hurt.

Rawhide doesn't add anything to performance and is simply a layer that reinforces any wee errors on the bow back and holds the bits together if it blows.

Bamboo would replace the sapwood altogether. The back would be decrowned(planed flat) before it was applied. There's quite a high crown on this since it came from such a narrow diameter log.
High crowns are a waste because only the centre of the back is taking full strain(where all the knots are ). Taking it off and backing with bamboo is quite appealing as it would fix the above, means that there was no chance of it blowing in tension and pretty much covers up the knots, making it easier for a monkey like me to get a decent bow out of a rough log.

Using glass fibre, putting it on over the sapwood back, would add a bit of performance and protect from blowing a bit more than rawhide would(maybe).

Sinew would be similar to glass but imparts a bit of pre-stress because it shrinks while drying. I only have enough for one bow and was hoping to use it on a bit of ash I've also been working on so finding out that it's not suited to yew is a good thing.

 

[Grooveski]

S0rry Toddy. If you mean why do folk back bows at all it's because the back of the limb is in tension and the belly is in compression.
Defects in the back make the limb prone to cracking/breaking. Putting a layer of something on the back which is stronger in tension than the existing wood makes it less prone to breaking.

Rawhide takes tension but is easy to stretch so it doesn't add performance.

Bamboo will take silly amounts of tension. A bamboo backing is more likely to cause the belly to fail in compression if the belly wood isn't suitable.

Fibreglass will try to spring back to it's original length so adds a bit to performance.

Sinew even more so because of the shrinkage when drying.

One of the reasons Yew is such a fine bow wood is because its heartwood is good in compression and its sapwood good in tension so it's essentialy backed to begin with.

 

[Snufkin]

Toddy, bows break because a splinter of wood lifts on the back of the bow (the side of the bow facing away from the archer) and runs into the wood causing it to go KABOOM!!!. A backing is applied to create a solid back to the bow so that splinters cannot lift up. In the case of rawhide it is protection only but sinew and fibreglass add to bow performance as Grooveski has explained.
Also short bows are often sinew backed as they are being forced to bend more to reach a specific draw weight and so are more likely to go KABOOM!!!. The wood is also more stressed so is likely to take more "set" (the bow wanting to retain its strung shape). Sinew helps fight this as it is highly elastic and trys to return to it's unstretched length, pulling the bow with it. Often sinew bows are "force reflexed" where the bow is essentially strung backwards before the sinew is applied so that it is forced to stretch even more.
Rawhide actually detracts from bow performance as you are adding nonworking mass to the bow limbs. The drop in performance is incredibly slight so unless you are going for a recordbreaking flight bow it's not worth worrying about.

 

[Snufkin]

Grooveski, It looks like you are going for a stiff handled style. I'd be inclined to go for a working handle design and perhaps give it mild recurves to keep the string angle good, and resist the string pulling off.

 

[Grooveski]

Just leaving options open!
There's still wood there for allsorts. Until I know what's going on with the back I've no idea what's going to happen to the rest of it.
I've got my heart set on a mini boo-yew Torges style number if all else fails, needed to leave some width to play with.

I'd hate to turn it into chips.
A Yew log at last... .
Chips....

 

[Snufkin]

Sensible to keep your options open. Watch your drawknife around the knots as they like to tear out. And remember that dust mask when it comes to sanding.

 

[Grooveski]

It'll likely be some time before I have to worry about that but thanks for the reminder.

While we're talking backings here's the wee ash number. Cut three months ago and hacked away on the spot so there wasn't much bark left to peel off(that was fun)....

....then dried for a couple of months before shaping it. It took on a couple of inches of reflex(was a straight log but the bow is from the tension side) and may even take on a bit more when the sinew goes on.
The profile pic was early in the evening, the handle and fades were more even when I hacked the belly down 'till it started bending...

...and there it sit's. It's a campfire whittling bow, don't work on it at home.
Again, looks like a stiff handle but really just haven't decided yet.

 

[Snufkin]

It'll likely be some time before I have to worry about that but thanks for the reminder.

While we're talking backings here's the wee ash number. Cut three months ago and hacked away on the spot so there wasn't much bark left to peel off(that was fun)....

....then dried for a couple of months before shaping it. It took on a couple of inches of reflex(was a straight log but the bow is from the tension side) and may even take on a bit more when the sinew goes on.
The profile pic was early in the evening, the handle and fades were more even when I hacked the belly down 'till it started bending...

...and there it sit's. It's a campfire whittling bow, don't work on it at home.
Again, looks like a stiff handle but really just haven't decided yet.

Ohh, that's really nice. How long is it?

 

[Grooveski]

It'll be 64" between nocks. If it hits 55lb at 27" I'll be well chuffed. Anything down to 45lb would be livable.

Talking as if it was a bow. It's still just a lovingly crafted tentpeg. Getting there though.

 

[Grooveski]

Spot the rot.

Knew the branch was from a windfall but guess it had been lying for a while. Can't believe I even posted a picture and didn't notice it, let alone scraped away at the sapwood wondering why some bits were tougher than others.

May be hope yet for the deep heartwood(he says, eagerly eyeing up the bamboo ).

Mmmm, chips.

 

[Snufkin]

It's more than likely that the rot is confined to the sapwood, I'd say remove it all and sinew it.

 

[Grooveski]

Look at the first decade of heartwood .

There are a few patches along the length where it was the same. The sapwood felt ok until I got down a bit then softened up.
I started prodding about with a scribe and one of the worst bits was right where I took the pic.
Not what I was looking at at the time though.

 

[Snufkin]

I looked again at the pics and I think you should still have enough wood for a decent weight bow once backed with either boo or sinew.