Trapping

[williwaw]

If I am laminating a bow, I am going to put the materials with more compressive strength near the belly

this is often done with wood laminated bows, for instance making a bamboo backed osage bow. 

It must be said that the the osage is "stronger" not in the sense that Mark is using the word, but more as Flem is referring to osage ability to bend further than other woods or have "elastic rebound". Different qualities both being described with the same word?

There is similarity between a laminated wood bow made with two different materiels and a glass bow with a trapped back. The back and belly are stressed differently to a useful effect.

Shredd mentioned earlier,

Here is something to think about...  If Trapping were such a sure thing in gaining performance then everyone would be doing it as a standard in building bows...

No one really responded to whether trapping is done universally in any particular designs. My question is related. Are there proven designs where different thicknesses of glass are used on the back or belly, or limbs glued up with asymmetrical stacks?

[Flem]

"I will be removing material from the belly side. Which in theory should shift the neutral plane and cause the back to work harder."

This is an erroneous statement for sure. let me clarify my thoughts on the neutral plane. My goal is to get it as close to the belly side as possible. To that end and within reason, the preference would be for a material to be of low hysteresis and compact/dense with the goal of using as little volume of it as possible in relation to the material on the other side of the zone. With the desired result of shifting the neutral plane to the belly, forcing more material into tension.

"Since wood and bow composites will return to a neutral position faster from being put in tension than being compressed"

This is also an erroneous statement. I should have said, materials suited for tension applications will generally, in the context and scope of bowyering, return to a neutral position faster than materials suited for compression applications

[Mad Max]

Flem
I'm not really following the thread but I was thinking

NOT that anyone would do this.
If you backed balsa wood with a bamboo slat the neutral plane would have to be the belly of the Boo,YES?
so any other wood the neutral plane would be moving towards the belly, Yes?
So Boo backed Ipe would be closer to the belly than Boo backed Osage?
From what I know Bamboo and Ipe are the best for a laminated Tri lam, so the neutral plane would be closer to the belly. If you used Ipe for the core that would move it even more to the belly?
JUST SAYING, I'm no Brainiac but it sounds like what I said would be true.?

[Flem]

Everything you said sounds correct, to me Mark. I'm talking about taking the next step, which for me is attempting to tweak the ratio of material volume, in tension vs compression, to the tension side. Why not take advantage of the compressive properties of the heaver woods and reduce it's mass in relation to the lighter more elastic Bamboo? Sure, the Osage does not need the bamboo to make a good bow, but if you are making a composite, the goal should be to maximize the attributes of each material. I don't recall anybody stating they would prefer a bow will more compressive resistance than tensile? If somebody has that preference, please share your rational.

I can't believe I got sucked into the Neutral Zone again! My character would have been killed off on the first Star Trek episode. The worst part is being sucked into the intangible. Yeah there are formulas for estimating the location of the neutral zone, but how thick is it? one cell? one molecule? one atom?
How do you locate something that itself can't feasibly be measured? And in a dynamic environment like the ones we create will bending limbs and fulcrums, does the plane shift progressively like the increase in resistance  to the bending force?
Some folks wish to be revealed the meaning of everything on their death bed, me, I would be fine with just the mystery of the neutral plane

[Mad Max]

 

[monterey]

or limbs glued up with asymmetrical stacks?

What is meant by "asymmetrical stack"?

[williwaw]

having different glass front and back or having a core that is not the same under the front as it is under the back.

[mmattockx]

I should have said, materials suited for tension applications will generally, in the context and scope of bowyering, return to a neutral position faster than materials suited for compression applications

This is possible, but I have never seen any testing of materials in this fashion. Have you seen/done any to confirm it?

From what I know Bamboo and Ipe are the best for a laminated Tri lam, so the neutral plane would be closer to the belly. If you used Ipe for the core that would move it even more to the belly?

Yes, that is likely correct and is the end result when you do a two lam bow using 'boo and ipe. Since most of the stresses are carried by the surfaces of the back and belly you may get a faster bow by doing a tri-lam with a lighter core wood and thinner back and belly lams because the core isn't doing much work aside from holding the back and belly surfaces in place while the limbs bend. I haven't yet made one to find out, though.

The worst part is being sucked into the intangible. Yeah there are formulas for estimating the location of the neutral zone, but how thick is it? one cell? one molecule? one atom?

There are no intangibles with the neutral axis, it is a geometric property of the cross section shape. Unless your limbs see significant shear deflections (which should not ever be the case that I know of for a bow) it doesn't shift or change in any way due to bending. The thickness is zero because it is a geometric plane. It doesn't have to be measured, it is a calculated property.


Mark

[Flem]

Its still intangible. The same way electricity is intangible. Ours is a tactile endeavor.

[Crooked Stic]

Al righty then my brain is hurting.

[mmattockx]

Its still intangible. The same way electricity is intangible. Ours is a tactile endeavor.

This is true. It certainly is a mathematical construction and is not something of physical substance.


Mark

[monterey]

having different glass front and back or having a core that is not the same under the front as it is under the back.

Thanks, I'm familiar with that concept but had never heard that terminology.

[monterey]

I'm not an engineer or scientist, but readily grasp the concept of the neutral plane.  It's my own thought that the ideal is to balance the tension and compression forces equally regardless of where the neutral plane ends up. 

I'm not sure if the balancing act can be done with a calculator given that wood varies from piece to piece within the same species but then again with our glass bows that may be less important than the comparative properties of the glass on each side with some consideration needing to go to what lay immediately under the glass.

[mmattockx]

It's my own thought that the ideal is to balance the tension and compression forces equally regardless of where the neutral plane ends up.

Can you explain or expand on what you mean by this?


Mark

[monterey]

in my mind it is a matter of what happens during draw and release.   IOW, tension is not overwhelming the belly and vice versa.  I visualize the action of the limbs the back pulling and the belly pushing. 

[williwaw]

I should have said, materials suited for tension applications will generally, in the context and scope of bowyering, return to a neutral position faster than materials suited for compression applications

This is possible, but I have never seen any testing of materials in this fashion. Have you seen/done any to confirm it?

It is common to see references made in bow building forums to the wood database or other similar resources when bowyers ask questions about the materiels we work with. The published data is certainly useful for the basics, but I often wonder if wood, when bent as far as we make it bend, can act in ways that are not well understood.
In the bow building world. we are our own testers when we build bows and make improvements as we go.

the preference would be for a material to be of low hysteresis and compact/dense with the goal of using as little volume of it as possible in relation to the material on the other side of the zone.

I have never found much information about hysteresis specifically in tension, but one only has to make a bow out of wet wood and watch the arrows drop more and more especially as we draw the bow further, to see hysteresis in action. Presumably increasing on the compression side as we can easily see the belly fail.

Any good ideas how we could test for hysteresis on the tension side?

[mmattockx]

IOW, tension is not overwhelming the belly and vice versa.

How would you know or sense if one is overwhelming the other?

The published data is certainly useful for the basics, but I often wonder if wood, when bent as far as we make it bend, can act in ways that are not well understood.
In the bow building world. we are our own testers when we build bows and make improvements as we go.

This is very true. We are doing things with wood that none of the standard reference sources ever considered. Pretty much all of the data available was collected with the intention of using wood as a structural material for buildings, bridges or aircraft structure. No one was thinking of taking a long, slender piece of wood and bending it to near 90 degrees then letting it snap back to the original shape.

Any good ideas how we could test for hysteresis on the tension side?

Not without big $$$ lab equipment. My gut feel is that hysteresis on the tension side is near zero. If you take a wood bow (either a selfbow or a lam bow) and cut the back off the belly you will find the the back typically stays straight or goes into reflex and the belly pulls well into deflex. All the damage to the wood appears to be on the compression side, which is what my gut feel says as well. Tension doesn't cause the same kind of cellular damage because a tension failure normally occurs in one single, violent event as soon as the tension limit is exceeded.


Mark

[monterey]

How would you know or sense if one is overwhelming the other

Well,  that's the crux of it.   Maybe a bow that delams would offer clues.

I'm going to take the path of more compression resistant material in the belly.  Starting with thicker glass.

One approach to knowing what is happening is looking for deflex (string follow).  My bows are primarily ASLs which makes string follow easier to observe and more likely due to the higher ratio of core lams. 

What if there is no follow observed over time?  Then an indicator would be the changes in draw weight over time.  It calls for careful record keeping.  If I can get to no string follow and no, or very little,  loss of draw weight I'll feel that balance has been reached.

Blacky Schwarz always  came up with a figure for hysterisis but I got no idea how he arrived at it.

[Mad Max]

quote from mm "This is very true. We are doing things with wood that none of the standard reference sources ever considered. Pretty much all of the data available was collected with the intention of using wood as a structural material for buildings, bridges or aircraft structure. No one was thinking of taking a long, slender piece of wood and bending it to near 90 degrees then letting it snap back to the original shape.

Horn bows were made 1000's of years ago using wood cores.

[mmattockx]

Horn bows were made 1000's of years ago using wood cores.

I understand that, but those were still crazy bowyers. All the wood test data we use comes from people that were using wood as a structural material that sees static loading for the most part and small deflections due to that loading. Bowyers are using wood in a completely different way and there has been precious little testing done for our uses. Our situation is not helped by the fact that we are trying to walk right up to the edge of failure with each piece of wood and that the variance even among pieces of wood from the same tree are very substantial.


Mark