Sinew layer compression and veneers
Hi there,
I am Outlaw from Belgium, new hre but I have roamed around the forum and site for a while, knowing whos who, reading first before initiating this topiC
I have never attempted a composite sinew horn bow endeavour, but I have been shaping surfboards for a while and know a couple things about this and that...I am an engineer (type of enginer undisclosed), and that also helps out. I have been doing pretty much self bows since 12. So, technically, I am in diapers here!
My first attempt is currently a turkish oversized in span bow, sinew and horn. Core is ash @ 1.2 cm, first layer is sinew is already poured, but I did something and I need to ask what the masters think of it:
I coverd the sinew/raw hide when liquid and warm with a red elm veneer of near 0.75 mm thick to give compression to the sinew layer, i wraped it up like if it was the horn belly (compressed it with thick rope), which has reduced th nominal sinew/rawhide layer to just barely to a mm and a half. I had to do this since being that part of the limb a traction zone, some compression there could increase the power, while keeping the weight low.
Doe it make any sense?
As well, i am experiencing absolutely no natural bending of the limb by contraction of the sinew when drying out.
Consequences?
Thanks very much, this is a fantastic and delightful living site...
I am Outlaw from Belgium, new hre but I have roamed around the forum and site for a while, knowing whos who, reading first before initiating this topiC
I have never attempted a composite sinew horn bow endeavour, but I have been shaping surfboards for a while and know a couple things about this and that...I am an engineer (type of enginer undisclosed), and that also helps out. I have been doing pretty much self bows since 12. So, technically, I am in diapers here!
My first attempt is currently a turkish oversized in span bow, sinew and horn. Core is ash @ 1.2 cm, first layer is sinew is already poured, but I did something and I need to ask what the masters think of it:
I coverd the sinew/raw hide when liquid and warm with a red elm veneer of near 0.75 mm thick to give compression to the sinew layer, i wraped it up like if it was the horn belly (compressed it with thick rope), which has reduced th nominal sinew/rawhide layer to just barely to a mm and a half. I had to do this since being that part of the limb a traction zone, some compression there could increase the power, while keeping the weight low.
Doe it make any sense?
As well, i am experiencing absolutely no natural bending of the limb by contraction of the sinew when drying out.
Consequences?
Thanks very much, this is a fantastic and delightful living site...
Quite hard to gasp what you are actually doing.
Please add pictures.
Please add pictures.
I dont know why I cannot add attachments, so I provide an schematic hereunder:
Beginning:
------------------------------------------------- Red Elm Veneer 0.75 mm
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
===========================
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& Sinew and Glue layer
[___________________________________] Core (Ash)
To this I wrap it, compressing the sinew layer between the veneer and core with very thick rope.
End (after compression):
-------------------------------------------------- Red Elm Veneer 0.75 mm
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& Sinew/Glue 0.75 mm (+ -)
[__________________________________] Core
Later:
Next layers will be like this as well, on the top of the one shown above. Im thinking on rawback hide covered with another veneer...
I hope this helps to picture it!
Beginning:
------------------------------------------------- Red Elm Veneer 0.75 mm
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
===========================
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& Sinew and Glue layer
[___________________________________] Core (Ash)
To this I wrap it, compressing the sinew layer between the veneer and core with very thick rope.
End (after compression):
-------------------------------------------------- Red Elm Veneer 0.75 mm
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& Sinew/Glue 0.75 mm (+ -)
[__________________________________] Core
Later:
Next layers will be like this as well, on the top of the one shown above. Im thinking on rawback hide covered with another veneer...
I hope this helps to picture it!
Vraagt Stephen Selby en hij zal dit probleem over attachment oplossen. Stuur hem de foto's die u nodig hebt :P
I am not expert as a lot of people here are competent, but as i understood you wrapped the bow by the rope after you put layer of sinew?. I didn't understand anything :oops: ...after you do first layer of sinew you need to give slightly bending to the bow(limbs) and let it dry in this position till another layers of sinew and till you reach ''circle'' and let it dry for months and months. I do not think you need to wrap it after you did it same as with horn.
Groeten uit Servie
Zoran
I am not expert as a lot of people here are competent, but as i understood you wrapped the bow by the rope after you put layer of sinew?. I didn't understand anything :oops: ...after you do first layer of sinew you need to give slightly bending to the bow(limbs) and let it dry in this position till another layers of sinew and till you reach ''circle'' and let it dry for months and months. I do not think you need to wrap it after you did it same as with horn.
Groeten uit Servie
Zoran
So you will end up having layers of veneer between your sinew layers? That sounds like a potential source of shear failure to me.
I also don't understand how compression keeps the weight low. You may increase the density, but the weight remains the same.
If you want to compress the sinew, you could try wrapping it with a thicker polyethylene film. The glue won't stick to it and you will not have useless veneer inbetween.
You should consider buying Adam Karpowicz's book, Ottoman Turkish Bows. It is very detailed on the materials, and contruction and tillering techniques.
Daniel
I also don't understand how compression keeps the weight low. You may increase the density, but the weight remains the same.
If you want to compress the sinew, you could try wrapping it with a thicker polyethylene film. The glue won't stick to it and you will not have useless veneer inbetween.
You should consider buying Adam Karpowicz's book, Ottoman Turkish Bows. It is very detailed on the materials, and contruction and tillering techniques.
Daniel
Daniel, thanks, appreciated.
I tell you why I do that: when working with non-natural occurring fibers (such as carbon, kevlar or any other) what works is the fiber and not the cohession material (glue, resins...) so what we usually do in the industry is to try to limit the amount of glue (this was also referred by Novotny in one of his interviews, when he was speaking about the minimum thickness of the sinew layers) to increase efficiency (ratio of the weight vs tensile strength).
I took it verbatim to the minimum amount needed, and for this endeavour, i have just reduced the layer to barely the maximum thikness of the sinew plus a small extra; this has been done by compression, by means of a very thin veneer on the top of the layer, bundl'ing it with rope (no problem of rope getting stuck to, since upper side of the veneer is clean, and core belly is clean as well). Of course I didnt try to bend the bow, since it still is drying, but just wanted to get a flavour of what experienced craftsman think of t.
As to the shear failure, i dont get it, the veneer will work in flexion, there is no shear stress there I reckon, can you ellaborate please?
Much appreciated!
I tell you why I do that: when working with non-natural occurring fibers (such as carbon, kevlar or any other) what works is the fiber and not the cohession material (glue, resins...) so what we usually do in the industry is to try to limit the amount of glue (this was also referred by Novotny in one of his interviews, when he was speaking about the minimum thickness of the sinew layers) to increase efficiency (ratio of the weight vs tensile strength).
I took it verbatim to the minimum amount needed, and for this endeavour, i have just reduced the layer to barely the maximum thikness of the sinew plus a small extra; this has been done by compression, by means of a very thin veneer on the top of the layer, bundl'ing it with rope (no problem of rope getting stuck to, since upper side of the veneer is clean, and core belly is clean as well). Of course I didnt try to bend the bow, since it still is drying, but just wanted to get a flavour of what experienced craftsman think of t.
As to the shear failure, i dont get it, the veneer will work in flexion, there is no shear stress there I reckon, can you ellaborate please?
Much appreciated!
When a bow is bent, there is shear stress everywhere except on the surface. It is largest in the neutral plane. This is from elastic beam theory for small strains.
I understand what you are trying to achieve with the compression. What ratio of glue to sinew mass did you use? The recommendation is 50/50 and that works without compression. You must be using less glue to get an improved fibre content and the compression is supposed to ensure wetting of all fibres despite a low glue content? Suppose there are some dry fibers. If you compress the sinew/glue layer, the dry fibres are compressed together. Does glue still manage to enter between them? The viscosity of the glue is surely higher than the viscosity of a laminating epoxy or similar glue, and it is also changes fast when the temperature drops, e.g. upon contact with a core that is not sufficiently warm.
It's an interesting approach. I would remove the veneer once the sinew is sufficiently dry before applying the next layer because I am very certain that thin veneer is mechanically completely useless. At least the one I have feels porous, brittle and weak.
Daniel
I understand what you are trying to achieve with the compression. What ratio of glue to sinew mass did you use? The recommendation is 50/50 and that works without compression. You must be using less glue to get an improved fibre content and the compression is supposed to ensure wetting of all fibres despite a low glue content? Suppose there are some dry fibers. If you compress the sinew/glue layer, the dry fibres are compressed together. Does glue still manage to enter between them? The viscosity of the glue is surely higher than the viscosity of a laminating epoxy or similar glue, and it is also changes fast when the temperature drops, e.g. upon contact with a core that is not sufficiently warm.
It's an interesting approach. I would remove the veneer once the sinew is sufficiently dry before applying the next layer because I am very certain that thin veneer is mechanically completely useless. At least the one I have feels porous, brittle and weak.
Daniel
Daniel, cheers, thanks and OLE. Lots of details and picky stuff in your mail.
Glue ratio: in excess of 50%, compresion does the rest (there is some spill over of glue). What i barely can control is the thickness of the layer; this time itproved to be a lot of compression, since one can hardly see underneath the veneer a really thin line corresponding to the sinew. Back in the days I did this with a vacuum pump, easily, controlled far more than with rope.
Sinew: wet. Nothing else.
The assurance that all fibers will be wet, is
1 - just a atter of some faith (since you can not see anything),and by doing the operation in my warehouse, which is at controlled temperature of 50-55 Celsius. All material at thermal equilibrium by being there hours (yes, veneer warm too).
2 - diffussion: placing the stuff near a heat source that assures a temp around 65 Celsius to allow the glue not to recristalize. This alllows bubbles to diffuse thru the glue up to the surface.
3 - steadily incresing the compression (this took me from 12 noon till 5 evening). I fess up that i exceeded a lot in the compression, layer of glue barely reaches 0.75 mm. Might be too brittle and disattach.
4 - Time, pressure and temperature controls the rest. After those five hours at 65C, i begin reducing the temp at a gradient step of 2.5 degrees/hour till room temperature reaches 25. I have it there for several days already.
5 - Veneer: you are right on the mechanical aspect. Seems useless at a first glimpse. Will be hard to remove though.
My first impression is that, is really hard to bend. I did just a very small test and feels (though flexible) but reeaaally stiff. Keep you guys posted, might add some photos if granted permission from the moderator.
Any further ideas?
Glue ratio: in excess of 50%, compresion does the rest (there is some spill over of glue). What i barely can control is the thickness of the layer; this time itproved to be a lot of compression, since one can hardly see underneath the veneer a really thin line corresponding to the sinew. Back in the days I did this with a vacuum pump, easily, controlled far more than with rope.
Sinew: wet. Nothing else.
The assurance that all fibers will be wet, is
1 - just a atter of some faith (since you can not see anything),and by doing the operation in my warehouse, which is at controlled temperature of 50-55 Celsius. All material at thermal equilibrium by being there hours (yes, veneer warm too).
2 - diffussion: placing the stuff near a heat source that assures a temp around 65 Celsius to allow the glue not to recristalize. This alllows bubbles to diffuse thru the glue up to the surface.
3 - steadily incresing the compression (this took me from 12 noon till 5 evening). I fess up that i exceeded a lot in the compression, layer of glue barely reaches 0.75 mm. Might be too brittle and disattach.
4 - Time, pressure and temperature controls the rest. After those five hours at 65C, i begin reducing the temp at a gradient step of 2.5 degrees/hour till room temperature reaches 25. I have it there for several days already.
5 - Veneer: you are right on the mechanical aspect. Seems useless at a first glimpse. Will be hard to remove though.
My first impression is that, is really hard to bend. I did just a very small test and feels (though flexible) but reeaaally stiff. Keep you guys posted, might add some photos if granted permission from the moderator.
Any further ideas?
I'd like to have such a hot room, too! I have to heat up the bath room and guess what I get to hear from my wife when she finds me working sinew and glue.
Perhaps you sand off the veneer, or remove it with a cabinet scraper. Could be hard when it is infused with glue.
Be careful about the temperature, if the sinew becomes too hot you might destroy the proteins (or whatever else, I'm not much of a chemist). I don't know the maximum temperature that still works, but I think 60?C must be rather close to it. I usually go for 50?C, my fingers don't like more than that anyway.
I am curious to see how it will turn out and see the pictures. I don't think you need special permission to post them.
Daniel
Perhaps you sand off the veneer, or remove it with a cabinet scraper. Could be hard when it is infused with glue.
Be careful about the temperature, if the sinew becomes too hot you might destroy the proteins (or whatever else, I'm not much of a chemist). I don't know the maximum temperature that still works, but I think 60?C must be rather close to it. I usually go for 50?C, my fingers don't like more than that anyway.
I am curious to see how it will turn out and see the pictures. I don't think you need special permission to post them.
Daniel
NOTE:
The destruction of sinew is easy to find out by it curling when glue is applied.
So the veneer is not just a glueing tool, but you actually mean to leave it in place?
Sinew bends a lot. The veneer not so much.
You cannot bend the sinew between the core and veneer more that the veneer will last. So you waste the sinew layers under veneer(s). They act like wood, but heavier and less stable.
If you want to make the core thicker by adding veneers you should add them on top of the core and then sinew on top of that.
Wood bends 0.7-1.1% sinew 5-10%
Surf board do not bend as much as composite bows and the contruction
probably has all different goals. (such as making it lighter so it would float.)
If you meant to use the veneer as glueing tool, You should take it away when the sinew is wet enough for it to be easy. After that you need to sand it and it takes some sinew with it.
The destruction of sinew is easy to find out by it curling when glue is applied.
So the veneer is not just a glueing tool, but you actually mean to leave it in place?
Sinew bends a lot. The veneer not so much.
You cannot bend the sinew between the core and veneer more that the veneer will last. So you waste the sinew layers under veneer(s). They act like wood, but heavier and less stable.
If you want to make the core thicker by adding veneers you should add them on top of the core and then sinew on top of that.
Wood bends 0.7-1.1% sinew 5-10%
Surf board do not bend as much as composite bows and the contruction
probably has all different goals. (such as making it lighter so it would float.)
If you meant to use the veneer as glueing tool, You should take it away when the sinew is wet enough for it to be easy. After that you need to sand it and it takes some sinew with it.