suggestion for backing Black walnut

[Dakota Kid]

I am looking to make a wood backed black walnut board bow. The choices for backing are hickory, red oak, or ash. I was planning to use hickory from the start, but in doing research, someone stated that hickory may over power the walnut.

Help me make up my mind fellas.

Thanks

[LittleBen]

Trap that back! I'd use whatever you have most readily available. Just trap the back well.

Going slightly wider in the limb will also help prevent compression failure.

[Dakota Kid]

My plan is to rip off simson's fancy boo backed erc design. From his pics it looks like he trapped the back so heavy it comes to a point. I will probably stick with my first instinct and use hickory, unless I hear a good reason not to by tomorrow.

thanks

[half eye]

Keep your hickory backing strip to a 1/16" or so and you will have no trouble at all...glue it on at about 1/8" and flat sand to roughly half that when dry.

Walnut will also make a fine self bow.
rich

[Dakota Kid]

The board I have is okay, but not perfect. I'l feel less nervous about failure with a backing. For this particular design I think a contrasting backing wood will do wonders for the aesthetics of the final project.


I wish I can find a small tree to get a stave from, but BW is heavily harvested in these parts. If people have them on their land, typically they want to keep them. In fact one of my stave collecting spots has a no walnut clause attached.

[DarkSoul]

I'd go with maple or ash, but I'm sure that hickory will work as well. Make sure to trap the back and to leave the belly flat.

[mikekeswick]

Red oak or ash are better bets than hickory. More important than wood choice is perfect grain on your backing.
The stronger the wood is in tension (resistance to stretching) then the less it works in a combo with a weaker in compression wood like walnut thus causing the belly to do more of it's fair share of work = chrysals. Hickory is super strong so you should trap it heavily. Red oak or ash won't need much trapping at all.

[bubby]

I disagree mike maple would ve the best vet to vack with but it wasn't in his options, use the hickory and trap it

[LittleBen]

According to Forest Products Laboratory data hard maple, red oak, and white ash have nearly identical tensile elastic modulus at around 12,000 MPa. Pignut Hickory has a tensile elastic modulus of 15,600MPa.

My point is that all the non hickory options mentioned should perform identically in terms of how likely they are to promote compression failure in the belly, which should be entirely dependent on tensile modulus. Which backing is strongest (i.e. Which can stretch farter before breaking) is another matter, but FWIW, maple, ash, and red oak, also have similar modulus of rupture (stress at failure), and strain at failure. So according to the data, they should be nearly identical, and straight grain probably matters a lot more than species.

If the hickory backing is trapped to 80% of limb width it should perform identically to unwrapped maple, ash, or oak.

Lastly, according to the data, an even better choice would be Elm for a backing as Elm is about 20% less tensile modulus than maple, ash, or oak, and nearly 35% less than hickory.

Sorry for the rant, it's the Engineer's plight .... We can only understand the world numerically .... Lastly this assumes the data is accurate, but since I have no reason to doubt the validity, I use it.

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch04.pdf

[bubby]

Ben from experiance most red oak is a terrible backer, and I've used it hickory maple and white oak, i would list it maple, hickory, white oak and i won't use red oak as a backer at all, not an engineer, just a redneck that builds bows and jmo

[LittleBen]

Bubby,

I'm with you 100%. I wouldn't choose red oak for a backer. If you're ripping backings down to thickness, it makes sense to use better wood which isn't anymore expensive (like maple and hickory as you mentioned). I also agree that the numbers don't really tell the whole story when you start bending wood near the point of failure. The only point I was getting at is how much trapping each wood might need if chosen compared to the others.

I had a couple white oak fail backing Ipe, so I abandoned that ... Always wondered if it was just a bad piece. Never tried maple. I live and die by hickory, it's my go to.

[GB]

I've only made a dozen or so backed bows and that's a small sample size and I still have much to learn.  I do like the idea of trapping the back if you're using hickory on a less dense wood.  I just finished a hickory backed maple pyramid bow (trapped) and am happy with the way it turned out.  I'd love to try maple as a backer, but have yet to find a nice, straight grained board.  I used red elm as a backer on ERC once and was happy with the results.  One of TBB books recommended it as a backer for lighter woods if I remember right.
Thanks for running the numbers, Ben.  That's something I never think about, but I always am interested in when someone else posts 'em.  More food for thought.

[bubby]

Gb try a maple selfbow if you can light and fast, one of the reasons it makes a good backer

[Dakota Kid]

Wow lots of good info since last night. Thanks to all. Ben don't apologize for a good answer with the data to back it up. That was exactly what I was hoping for. I'd love to try the maple it looked really pretty contrasted against the walnut, but alas I'm out of stock. I do have some really nice ash, grain is wonderful and I've already made two nice shooters from the batch. The hickory I was going to use is actually the toughest piece I've seen since I began using it, so I'll save that lumber for another project.

Does grain spacing on the backing wood come into play at all here? Some is more spaced than others. Should I use the tight stuff as I would if I was doing a selfie, or should I try to match the spacing to the piece of walnut? I'd just go for it and learn from my mistakes but, I only have enough walnut for two tries. It would be nice to do it right on the first one.

[mikekeswick]

Well i've used red oak a few times and it worked just fine as a backing wood for 'not so dense' bellies. As always the grain must be straight and quarter sawn is best with this heavily ring porous wood.
Maple wasn't on the list and I didn't say that my advice was about the 'best' wood to back his walnut with.....I listed my opinion on the order of his options?
Maple isn't 'lighter' than red oak or ash? Average density of about 0.6 - 0.65 s.g. Maple makes a good selfbow because it's compression/tension characteristics are similar!