Over-powering discussion if you please....

[PEARL DRUMS]

This over-powering thing has be baffled. I didnt want to hi-jack that HBRO thread from that fella. If some of us believe the back over-powered the core that would mean that 1/8" of hickory is stronger than (roughly) 1/2" red oak correct? That would make hickory 4x stronger.

[parson]

I'm in the process of finishing one that fits that definition- red oak board bow with 1/8" hickory back on it. It's around 55# at 28". I hope it holds up. I have tempered the belly, that oughta help.

[Buckeye Guy]

Pearl
I think you may have over simplified this !
the part of the bow that is over powered is just a small portion of its thickness .
In your example the belly could be over powered by the hickory + most of the rest of the oak ,then add in the glue line factor and the leverage factor for thickness
consider the compression vs tension ,and a few other things that could be going on and yes there might be some over powering going on !!!
So what was it you wanted to say ? Hickory is better than red oak for bows ? with that I will agree !!!
Have fun my friend !
Guy

[PEARL DRUMS]

Thansk Guy. I just wanted to better understand this over-powering thing. I underatand that only a small portion of the surface wood does all the compressing and stretching. With at being said why does it matter how thick your back is when only 'x" amount is doing all the work? I have only built maybe 8-12 hard backed bows and none failed or chrysaled, did I get lucky?

[mikekeswick]

Remember that most of the 'work' either compression or tension is being done by the very surface of the back/belly. Really the rest of the thickness is just a spacer - think about a steel I beam - they aren't that shape for no reason. Have a look at stress/strain equations. 
I keep thinking how it would be possible to make a bow with an I-beam cross section....it would likely be the fastest bow ever made....lateral stability would be the issue

[mikekeswick]

A lot is said about thin backings....narrower backings would be a better way to think. Thin or thick doesn't make much difference in my opion.

[MWirwicki]

Drums:  I imagine you're going to get a bunch chiming in, here. 

Nevertheless, my understanding it that there is a relationship between the compression/tension properties of a wood species and where the neutral plane occurs, in the bow.  When you back a bow or introduce a second species of wood, it affects the neutral plane by shifting it either more towards the belly or more towards the back.  The differing compression/tension qualities of one wood species to the other can move the neutral plane too far in one direction (or the other) thereby causing an overpowering affect.  This is why there are good and poor combinations.  I myself would like to see a "cheat sheet" indicating those that are good and maybe those that are bad. 

It can be a confusing topic.  In TBB Volume I, Tim Baker discusses tension, compression, trapping and The Poisson Effect under Bow Design & Performance.  It is a worthwhile re-read.   

[PEARL DRUMS]

Excellent info Matt, hopefully I do get a bunch of chime in's, I love to learn. I may have to re-read Tim's chapter tonight! So maybe it isnt the backing or cores thickness as much as the wood combo used. 

[MWirwicki]

Yes.  Although an exaggeration to ponder is that if you backed a red oak future bow with a 3/8-inch hickory backing, you might not have any red oak remaining after tillering. 

[Matt S.]

I think Matt summed it up rather nicely, so let me put my 2 cents in and try to "murky things up a bit"
Imagine the two woods glued up and being bent. The harder wood will resist the bend more than the softer wood, but both woods have to bend the same amount. If the harder wood (hickory in this case) is resisting the bend, then that means the softer wood (red oak) is taking on more work, and, as we bowyers say, is being over powered.
Now to get the hickory to do its fair share of the work, we have to coax it to not resist being bent. How do you do that? Well, we all know that thin wood will readily bend and thicker wood doesn't, so thin the hickory!
I think this is another way of visualizing the relationship between tension and compression forces and the neutral plane.

At least this is how I sort of understand it, but I'll admit, I'm no expert! 

[PEARL DRUMS]

More good info Matt S., thanks man. Matt W my first hard backed bow was just that, except its still kickin' because of light draw weight and long length.

[Buckeye Guy]

Mike
 the I beam thing has been done before and if my memory is correct the lateral stability ended up being relieved thru adding a extreme light weight wood to fill in the sides so some of the
benefit was lost and allot of work was consumed
since I am lazy I don't see it as that great a thing, but the color effects could make it worthwhile!
If you folks keep jogging my memory I may actually have something to say once and awhile!
Have fun
Guy

[Gaur]

good discussion.  I like Matt S simple definition for dummies like me 

The yumi bow is kind of like a I beam as Buckeye described it with the stacked boo core and a lighter wood like mulberry along the edges I guess.

[kiwijim]

Some keep in mind that all wood is much stronger in tension than compression. Think about the last horizontal branch you cut for a stave. Notice how the pith was not in the center of the branch, but rather near the upper surface? This is because the branch needs alot more compression wood than tension wood to hold itself up.  Wooden bows are the same.

[PEARL DRUMS]

Very insightful Jim. I never even thought about that, or looked at the sapwood that way.