Hickory, Ipe and Lemonwood...

[hunterguy1991]

Dennis, I think some serious finite element analysis would need to be done on the different cross sections with varied laminations. Something I would he interested to do but unfortunately lack the program to accomplish.

my best be at the moment would be to make another of these bows but use a less dense and stiff core lam of the same thickness and glue up with the same reflex to see what that bow held after tillering/shooting.

an interesting thought tho, my 142lb warbow with an ipe belly holds more reflex that this one. It has a lemonwood core lamination.

possibly worth a trip back to uni to consult with a few lecturers and get their thoughts on the matter.

[Dennis La Varenne]

Colin,

Personally, I am not surprised at the result you had with your Ipe bellied ELB. I reckon that Ipe is far superior in compressive strength than commonly available Lemonwood, at least it seems to on my two bows. Its elastic limit is probably a good bit higher than Lemonwood on average, so deformation of its internal structure probably requires a much greater bending load than you are subjecting your bows to I guess.

Interesting to hear from your Uni blokes, though.

[Nezwin]

Reading all this about Ipe & set, I've been pondering a few things for a while that might be relevant...

Maximum Shear Stress occurs at the Neutral Plane. If the use of Ipe has caused less set to be taken, it would be as a result of Ipe's performance in Shear. Stick with it here because it goes off on a tangent now...

I think there might be two types of compressive strength in timber - one as an inherent property (call it the 'x-factor') and another which is a function of density.

Yew & Lemonwood are examples of 'x-factor' timbers - inherently strong as a result of certain properties. They also take appreciative set. To a lesser degree, I believe Osage has this 'x-factor', although it is also very dense, so takes less set. These are also fairly 'springy' timbers.

Density Strong (in compression) timbers are legion - Ipe, Spotted Gum, Ironbark, etc. They take less set, for the most part, too. There's exceptions ofcourse, and those timbers which sit in the grey area between, but as a rule of thumb this might work.

Now, remembering that wood is made up of the wood fibres themselves, the glue holding the fibres together and the voids between these (Colin, you might consider this in the same way that a geotech material is made up of solids, liquids and voids of which the solids can be graded and classified as silicates or non-silicates), each of these respond differently to loading. These properties would be subtly different again in late wood & early wood.

In less dense timbers I'd assume the fibres contribute less to the overall mass and properties of the timber but (in the case of Yew, for example) the glue holding the fibres together exhibits some kind of 'x-factor' which provides compressive strength, or rather, elasticity (I think). However, being less dense, there are more voids and under compression the cells realign and cause permanent deformation, ie, set.

In denser timbers I'd assume that the fibres are closer together, consisting of an overwhelmingly dominant percentage of the timber mass & contributing a greater proportion of their properties to the overall properties of the timber. With little in the way of voids between the fibres, there is little space available for the cells to move into under load and therefore there is little permanent deformation, ie, set.

So what does this mean for set in a bow with an Ipe core? The Ipe would be under maximum Shear Stress at the core but with little in the way of internal voids for the cells to realign into, it takes very little set. Lemonwood, in the core, would have those internal voids to realign into and would subsequently take set. At the core, however, it is to be remembered that the material is being both pushed together and pulled apart, so the proximity of the fibres and proportion of voids would come into play here as the dominant factor. It's all to do with the ratio of fibres/voids/internal glues with different species fibres & glues having different properties. For Yew, it would seem the glue is very elastic and strong.

With consideration for direct heat bending, with Yew the space between the cells allow the heat to transfer through with little difficulty. I'd predict the same is not indifferent for Lemonwood, albeit to a lesser degree perhaps. With denser timbers require steam bending as there's little in the way of space between the cells for heat to penetrate through and more time is required for adequate temperature change.

I'm pretty cavalier with my terms and I've no idea how this hypothesis would stack up scientifically, but by classifying wood as a composite of wood fibres, internal glues & voids, it would seem to clear some of the murkiness on a non-homogeneous material. Happy to be proven (or even 'my experience says otherwise') wrong! I'm by no means a bowyer but I do appreciate some materials science concepts.

Edit: I just saw the comments on the second page which I believe covered most of the above but in far fewer words...

[bigbob]

From my academically challenged perspective and lacking any sort of engineering nous your hypothesis Nezwin certainly seems to hold a deal of merit. I am not knowledgeable enough on this subject to add to it, merely ingest,digest and gather useful information. I will keep watching this post with interest however.

[Dennis La Varenne]

Nezwin, like Big Bob, I think your hypothesis has merit, despite my previous arguments above. It is perhaps the most plausible of any in regard to central stiffeners and deserves some kind of follow-up.

However, the final proof of efficacy is that on average, bows made with a central stiffening layer develop significantly less string follow. My 3 examples previously instanced above did not support the hypothesis, but likewise, I do not know the building process of the bowyer who may use a technique which overstrains the bow before finishing.

[greybeard]

The following # image shows the end grain at 10 times magnification and the average dry weight of some of the timbers mentioned on this site in relation to bow making.

# Source; http://www.wood-database.com/

End Grain X 10 Zoom And Kg per cu-m.jpg (166.78 KiB) Viewed 4506 times

The individual cellulose fibers are extremely small and are tubular in cross section.

Softwood Hardwood Fibre Length.jpg (35 KiB) Viewed 4506 times

*Cellulose

It is a high molecular weight, stereoregular, and linear polymer of repeating beta-D-glucopyranose units. Simply speaking it is the chief structural element and major constituents of the cell wall of trees and plants.

*Lignin

A complex constituent of the wood that cement the cellulose fibers together. Lignin is brown in color. Lignin is largely responsible for the strength and rigidity of plants.

*Hard Wood

Wood from trees of angiosperms class, usually with broad leaves. Trees grown in tropical climates are generally hardwood. Hardwood grows faster than softwood but have shorter fibers compared to softwood.

*Softwood

The trees classified as softwoods have needle like or scale like leaves that, with a few exceptions, remain on the tree all through the year. Hence softwood trees are sometimes called evergreens. Botanically, they are known as gymnosperms, from the Greek word meaning "naked seeds." Instead of bearing seeds from flowers, gymnosperms have exposed seeds in cones.
Generally grown in cold climates, softwood grows slower than hardwood but have longer fibers compared to hardwood.

*Compression Wood

This wood occurs on the lower side of the branches and leaning trunks in soft wood. Compression wood contains more lignin and less cellulose compared to normal wood. For a picture of compression wood please go to; http://www.treedictionary.com/DICT2003/ ... ood-1.html

*Tension Wood

This wood occurs on the upper side of the branches and leaning trunks of hard wood. Tension wood contains more cellulose and less lignin compared to normal wood. For a picture of tension wood please see link above.

For more information click on the link below.

*Source; http://www.paperonweb.com/wood.htm

Daryl.

[Dennis La Varenne]

Good post there Daryl. I have always referred to wood fibres being held together in a matrix of what I have thought was referred to as a 'plastid' which is probably technically correct, but obviously among the woodies, the fibres are cellulose and the matrix material is lignin. I always thought is was there other way round but there you are.

I knew about the tension and compression woods as they lay in the tree. The compression wood usually takes a big set when drying because it reverses its curvatures in the tree and likewise the tension wood dries into a big reflex which is handy for bowmaking. One of the very best of my Osage flatbows was made from a 60" length of tension wood which had a dried reflex of 5" and held a bit over 2" after shooting. Pisser of a bow too. Gosh it was quick.

[Nezwin]

Nezwin, like Big Bob, I think your hypothesis has merit, despite my previous arguments above. It is perhaps the most plausible of any in regard to central stiffeners and deserves some kind of follow-up.

However, the final proof of efficacy is that on average, bows made with a central stiffening layer develop significantly less string follow. My 3 examples previously instanced above did not support the hypothesis, but likewise, I do not know the building process of the bowyer who may use a technique which overstrains the bow before finishing.

Dennis,

The hypothesis is just that - a hypothesis. And if the results don't support the hypothesis then the hypothesis should be junked. Really, it was just a way for me to get some thoughts out there that had been buzzing around in my head. They rarely make a whole lot of sense but it eases my mind to have them out! I did the same with the 'above & below neutral plane' thread (sorry for hijacking that, Daryl), someone happened to do something which loosely applied to something I'd been considering for a week or so. Doesn't mean I'm right but it does get the discussion going. One sword sharpens the other, eh?

The following # image shows the end grain at 10 times magnification and the average dry weight of some of the timbers mentioned on this site in relation to bow making.

# Source; http://www.wood-database.com/

End Grain X 10 Zoom And Kg per cu-m.jpg

The individual cellulose fibers are extremely small and are tubular in cross section.

Softwood Hardwood Fibre Length.jpg

*Cellulose

It is a high molecular weight, stereoregular, and linear polymer of repeating beta-D-glucopyranose units. Simply speaking it is the chief structural element and major constituents of the cell wall of trees and plants.

*Lignin

A complex constituent of the wood that cement the cellulose fibers together. Lignin is brown in color. Lignin is largely responsible for the strength and rigidity of plants.

This is interesting and gets to the main point of what I was hovering around in the previous post -

Assuming all woods are essentially composites of Cellulose fibres in a Lignin matrix (or Plastid, as Dennis has rightly termed it), what is it that changes between these Plastids that provide different properties?

For instance, Hard Rock Maple and Yew have ADW's of 705 kg cu/m yet exhibit vastly different properties under loading. What specifically is different between the fibres and/or the lignin in these timbers? And what is different between how these mesh together (aside from the obvious differences shown in the picture above) in the Plastid?

I would imagine that there is a discernible difference in yield, quality, colour, weight, etc of paper when using different source products so I imagine an individual with a background in paper manufacturing would have more insight into this...

From an Engineers POV, it would seem the fibres function in a way not dissimilar to the fibre in a composite material (carbon, glass, kevlar, etc) and the Lignin acts in a similar manner to the resin (epoxy or polyester, for the most part). Reinforced concrete is another example of a commonly used composite, and perhaps a better example, as the Lignin-analogy here is a composite itself of voids, cement, sand and graded gravel.

[Dennis La Varenne]

Neil,

I do understand what an hypothesis is and its purely propositional nature. Just the same, it has started me thinking too. Like you, I have thought of wood as having similarities to fibreglass and other reinforced composites.

[greybeard]

.....Assuming all woods are essentially composites of Cellulose fibres in a Lignin matrix (or Plastid, as Dennis has rightly termed it), what is it that changes between these Plastids that provide different properties?.....

Hopefully this line of discussion will not derail the topic.

From my understanding plastids nourish the plant and the lignin binds everything together.

*The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a major double-membrane organelle [1] found, among others, in the cells of plants and algae.
Plastids are the site of manufacture and storage of important chemical compounds used by the cell. They often contain pigments used in photosynthesis, and the types of pigments present can change or determine the cell's color.
They have a common origin and possess a double-stranded DNA molecule that is circular, like that of prokaryotes.
Those plastids that contain pigments can carry out photosynthesis. Plastids can also store products like starch and can synthesise fatty acids and terpenes, which can be used for producing energy and as raw material for the synthesis of other molecules.
For example, the components of the plant cuticle and its epicuticular wax are synthesized by the epidermal cells from palmitic acid, which is synthesized in the chloroplasts of the mesophyll tissue.[2]
All plastids are derived from proplastids, which are present in the meristematic regions of the plant.
Proplastids and young chloroplasts commonly divide by binary fission, but more mature chloroplasts also have this capacity.

1 Plastids_types_en_svg.jpg (54.17 KiB) Viewed 4483 times

* Source; https://en.wikipedia.org/?title=Plastid

+ Lignin is an organic substance binding the cells, fibres and vessels which constitute wood and the lignified elements of plants, as in straw.
After cellulose, it is the most abundant renewable carbon source on Earth.
Between 40 and 50 million tons per annum are produced worldwide as a mostly non commercialized waste product.
It is not possible to define the precise structure of lignin as a chemical molecule. All lignins show a certain variation in their chemical composition.
However the definition common to all is a dendritic network polymer of phenyl propene basic units.
There are two principal categories of lignin: those which are sulphur bearing and those which are sulphur-free.
It is the sulphur bearing lignins which have to date been commercialized. These include lignosulphonates (world annual production of 500,000 tons) and Kraft lignins (under 100,000 tons p.a.).
Due to the lack of suitable industrial processes, the sulphur-free lignins are as yet non-commercialized.

0-Formulelignin.jpg (47.84 KiB) Viewed 4483 times

+ Source; http://www.ili-lignin.com/aboutlignin.php

# Lignin and cellulose work together to provide a structural function in plants analogous to that of epoxy resin and glass fibres in a fiberglass boat. The fibrous components, cellulose or glass fibres, are the primary load-bearing elements while the matrix, lignin or epoxy resin, provides stiffness and rigidity. Thus trees (lignin content between 20% and 30% of dry weight) grow much taller than grasses (lignin content below 20%) before they bend under their own weight.

Beyond the structural function, lignin plays several other important biological roles in plants. Because it is much less hydrophilic than cellulose and hemicellulose, it prevents the absorption of water by these polysaccharides in plant cell walls and allows the efficient transport of water in the vascular tissues. Lignin also forms an effective barrier against attack by insects and fungi.

Kraft Lignin After Filtration And Washing.jpg (22.12 KiB) Viewed 4473 times

# Source; http://www.lignoworks.ca/content/what-lignin

....I would imagine that there is a discernible difference in yield, quality, colour, weight, etc of paper when using different source products so I imagine an individual with a background in paper manufacturing would have more insight into this......

The different types of pulping processes generally determine pulp ‘brightness’ and fibre length. Follow the link for more a comprehensive overview.

http://www.paperonweb.com/gradepl.htm

Daryl.

[Dennis La Varenne]

Daryl,

That is a very interesting post indeed.

Re the word 'plastid', I found it used by Bootle in his book - "Wood in Australia". I read its use to be a sort of generic term for a how your post describes the purpose of lignin. It seemed to refer to a group of materials having plastic properties rather than to plants specifically.

However, consulting both Merriam Webster and Oxford Dictionaries, both agree with what your post contains. Perhaps engineers have their own use for the term.

[hunterguy1991]

I was just reading through a post about some of Daryl's Asiatic style bows that he made some time ago and he made the comment that a bow he made which utilised an ironbark core seemed to have better recovery (think that's the word he used in the post) than a bow that did not...

Not sure if the other bow had a less stiff core material or no core material or if the bows were the same draw weight or not but I find the comment interesting and in line with my experiences currently.

[Dennis La Varenne]

Colin,

I'm not surprised at that. It's very strong stuff with one of the highest ratings among the indigenous timber varieties. All of the so-called 'Iron Barks' rate as very strong with not much between any of them that the published figures show.

[greybeard]

Dennis and Colin,

During the drying/seasoning of timber is it possible a large percentage of the plastids dry out/dissipate while all the lignin remains in the timber.

.....The fibrous components, cellulose or glass fibres, are the primary load-bearing elements while the matrix, lignin or epoxy resin, provides stiffness and rigidity. Thus trees (lignin content between 20% and 30% of dry weight) grow much taller than grasses (lignin content below 20%) before they bend under their own weight.......

Perhaps timbers that display string follow are low in lignin content whereas those with high lignin content resist more to taking a set. There appears to be very little information available on the lignin content in the various woods.

*Maclura pomifera

"The present results are in agrees with the previously reported results,where chemically the wood contains of 41.22 % lignin and 0.33 % ash[24]. Furthermore, the content of cellulose was lower than the amount regular appears in the hardwoods. Previously, it has been observed that at the same height level, the lignin, extractives and ash decreased from pith to the bark, while cellulose increased by increasing the age. This is supported by the fact that the juvenile wood has higher lignin and lower cellulose content compared to the mature wood. The extractives and ash content of juvenile wood was also found to be lower than the mature wood [25, 26]."

[24] Marchan, F. J. 1946. The lignin, ash and protein content of some neotroplcal woods. Canbbean Forests 7:135-138.
[25] Gabriell, J; Tampson, M; Figueira, J. 1999. Within-tree variation of heartwood, extractive and wood density in the Populus de1toides hybrid. Wood and Fiber Science 33(1): 3-8.
[26] Sliupe, F; Clioong, T; Groom, H. 1996. Difference in some chemical properties of innerwood and outerwood from five populus species. Wood and Fiber Science 29(1): 91-97.

*Source; JOURNAL OF FOREST PRODUCTS & INDUSTRIES, 2013,

With regards to the Asiatic bows it was mainly a case of improvising during the building process as there was little information available at the time for an all bamboo bow.

The upper bow in the picture was of all bamboo construction and it took a fair amount set, the lower bow had an ironbark lamination as well as two of bamboo.

Asiatic Static Tip Bows.jpg (73.17 KiB) Viewed 4447 times

As you can see the bows are a little different in profile which could account for differences in performance. Additionally I believe the hardwood siyahs added too much mass to the ends of the limb.

In defence of the all bamboo bow the outcome could have been different had I known about heat tempering bamboo.

Back then it was a matter of learning by experimentation.

Daryl.

[Dennis La Varenne]

Daryl,

That is a very interesting observation about the differences between juvenile and aged woods. Curiously, my two all bamboo bows have been miserable failures where the belly was a Bamboo lamination despite being told that the material had been heat tempered. Even so, I should have learned the process myself and applied it to be certain. I suspect that what I was told was not the case in fact.

I recently bought on eBay, an all bamboo laminated bow with a hard wood glued on handle which is only 60 inches long. I had to take it as well as the better bow I actually wanted. However when it arrived, it looked like rubbish and was barely 1" wide at its widest and hardly narrower at the appallingly cut nocks. When I tried to bend it, it was barely bendable. I was amazed. Jeff Challacombe had a go with the same result. He spotted something I had missed. It was that the thick belly lam was made from vertical flooring obviously of some superior kind backed with the usual rind backing. It is an absolute brute to try to draw.

Jeff remarked to me that flooring was usually pretty spongy in his glassed bows but this thing was something else. The seller commented on eBay that it was a very quick bow. I am not surprised.

My best ever flatbow of 60" length was made from a very very juvenile log of Osage cut not far out of the town of Wangaratta in Victoria by myself, Jeff and Col (Ribtek) Graham. It had 5" of reflex and retained 2" of that despite drawing in excess of 70lbs at 26" when I could draw such draw weights. I later sank it to 65lbs and the bow still retained its reflex. Jeff Challacombe made a slightly narrower and longer flatbow from wood from the same stock and it too shot almost as well as his good glassed bows as he told me. His bow had rather Mollegabet ends which were deflexed, but it still shot astonishingly quickly. Rightly or wrongly, I attributed that to the observation that this wood had a very high percentage of latewood in its makeup and very thin layers of early (Spring) wood. Both of our bows had barely two growth rings in the thickness of their limbs and towards the tips, mine thinned down to one growth ring.

This Osage was cut from suckers which had begun to coppice from a larger felled tree. They were perhaps 5 - 6" diameter. The leaves were huge and bright green as happens to Osage when it is very young - the later older trees having much smaller and darker leaves somewhat like those from Elm trees.

It was amazing stuff which we have not ever got again. But that does not over-ride your material above as a general observation of course.