Cores breaking problem
I recently got out my first Turkish bow which had always had problems - kasan eyes too thick, twist and dodgy sinew layer.....and decided I could fix all the problems in one go by removing the sinew, adjusting the core and then resinewing it. However once I removed the sinew I saw that the core had been failing in multiple places along the 'back' and had cracks going across it. After inspecting it fully I found about 15 of these cracks so my plans to fix it went out of the window!
Thinking back I have had 3 failure like this where the core has failed.
Especially frustrating was my last Turkish bow, this one didn't need a single correction once braced, no twist at all. However once I got it to around 25 inches I heard the dreaded 'tick' and the core cracking turned out to be the problem once again. This core was made from prunus avium.
I'm presuming that the cause has to be the sinew layer simply being too thin? However I'd like to have this confirmed before spending all that time making another. I am fairly certain that the sinew was 2mm thick along the center of limbs as per Adams recommendations in his book.
Thinking back I have had 3 failure like this where the core has failed.
Especially frustrating was my last Turkish bow, this one didn't need a single correction once braced, no twist at all. However once I got it to around 25 inches I heard the dreaded 'tick' and the core cracking turned out to be the problem once again. This core was made from prunus avium.
I'm presuming that the cause has to be the sinew layer simply being too thin? However I'd like to have this confirmed before spending all that time making another. I am fairly certain that the sinew was 2mm thick along the center of limbs as per Adams recommendations in his book.
Say, how much sinew did you use for the bows each? Like, how many grams?
I am wondering whether this is a suitable core wood for a Turkish bow over 60 lbs. I remember it being used in longer bows which were not quite as stressed. I know there can be many other reasons both mechanical and structural, but I think Adam once told me about this in an email.
I've always tried to get close to the 100 grammes recommended by Adam in his book. However this first bow was a long time ago and I really can't remember exactly how much I used? I didn't get the back anywhere near flat enough though.
The core used on my last Turkish bow was maple however I don't think I used the full 100 g on this bow - more like 70 g.
Has anyone else come across this problem of the cores cracking? Is it just the sinew thickness that is at fault? Eg the top of the crown of the core is too far above the neutral plane?
The core used on my last Turkish bow was maple however I don't think I used the full 100 g on this bow - more like 70 g.
Has anyone else come across this problem of the cores cracking? Is it just the sinew thickness that is at fault? Eg the top of the crown of the core is too far above the neutral plane?
I guess the same could happen if the sinew is not stretched out enough on the bow? I doubt that is your problem though. Perhaps you could also pull the tips together more inbetween the layers, to put more of the stress on the sinew.
Interesting thought. Maybe this could be the problem.
I have just been exercising my latest bow and...i've heard the dreaded 'tick' again,a whiter (than it should be) area has appeared on the sinew and it's acting weak there. I suspect the same problem.
The core was made with bulletwood for the handle, maple sals and black locust outer limbs. It's not a Turkish design more like a Magyar bow without reflexed outer limbs.
I have just been exercising my latest bow and...i've heard the dreaded 'tick' again,a whiter (than it should be) area has appeared on the sinew and it's acting weak there. I suspect the same problem.
The core was made with bulletwood for the handle, maple sals and black locust outer limbs. It's not a Turkish design more like a Magyar bow without reflexed outer limbs.
Would it be possible for you to use an outer growth ring piece as your bending portion?
Seems like if the core was totally sound like a good selfbow the problem could be mitigated even if other growth ring configurations have proven to hold up for others.
Seems like if the core was totally sound like a good selfbow the problem could be mitigated even if other growth ring configurations have proven to hold up for others.
I d go for the more sinew plan.
old bows have quite lots of sinew.
old bows have quite lots of sinew.
Mike
What was the dimension on this bow's limb. Mean horn-core-sinew thickness and width.
Was that wood natural seassoned?
I think the back of the bow was overstressed.
May the core was too thick and the sinew too thin for that.
If the horn thick and the core too that indicate more stress on the back.
It needs more sinew.
As you know there is a neutral line in the core of the bow.
If this line going towards the back or the belly of the bow (from the center), thats make trouble as you mentioned before.
I dont think you've made any error with the wood as a selfbow expert.
But I wouldn't use black lochust for the limbs in a hornbow.
What was the dimension on this bow's limb. Mean horn-core-sinew thickness and width.
Was that wood natural seassoned?
I think the back of the bow was overstressed.
May the core was too thick and the sinew too thin for that.
If the horn thick and the core too that indicate more stress on the back.
It needs more sinew.
As you know there is a neutral line in the core of the bow.
If this line going towards the back or the belly of the bow (from the center), thats make trouble as you mentioned before.
I dont think you've made any error with the wood as a selfbow expert.
But I wouldn't use black lochust for the limbs in a hornbow.
The Koreans use Black Locust for siyahs.. Maybe that's the part Mike means by "outer limbs"?
I know they use mulberry.
Bl is a new info for me .
Bl is a new info for me .
I only have a minute now....
I will take some pictures to give you all a better idea this afternoon.
I will take some pictures to give you all a better idea this afternoon.
I suppose it must be down to not using enough sinew although i'm sure i've had at least 2mm along the center of the back on all my bows.
The bending sections of the newest failure was hard maple (kiln dried board but only glued in reflex no steam bending) and the 'levers' for want of a better word were black locust.
Fusizoli - The limb at mid-sal was 33mm wide and 12mm thick. The horn was around 4mm, maple 6mm and the sinew 2mm thick.
The bending sections of the newest failure was hard maple (kiln dried board but only glued in reflex no steam bending) and the 'levers' for want of a better word were black locust.
Fusizoli - The limb at mid-sal was 33mm wide and 12mm thick. The horn was around 4mm, maple 6mm and the sinew 2mm thick.
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These pictures show the Turkish bow with the sinew stripped off and the other bow that I suspect has had a core failure. As i'm sure you can all see the pencil indicates the problem areas.
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These pictures show the Turkish bow with the sinew stripped off and the other bow that I suspect has had a core failure. As i'm sure you can all see the pencil indicates the problem areas.
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These pictures show the pretty major failure of the core on my Turkish bow. This is the bow with an air dried cherry (prunus avium) core. The draw weight was around 60# @ 28 and it was 48 inch ntn.
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These pictures show the pretty major failure of the core on my Turkish bow. This is the bow with an air dried cherry (prunus avium) core. The draw weight was around 60# @ 28 and it was 48 inch ntn.
Think the problam made those thing I ve mentioned before. This is not a wood fault.
4mm horn 6mm core 2mm sinew is not a good proportion
4mm horn 4mm core schould work with 2mm sinew
or
5mm horn 5mm core 3mm sinew....
Schould put a thicker sinew layer on it but it will push the neutral plane to the horn glue line. Especially if the horn is thin.
6mm core is good for warbows well ower 100#
But waiting for what the pro bowyers say ;)
4mm horn 6mm core 2mm sinew is not a good proportion
4mm horn 4mm core schould work with 2mm sinew
or
5mm horn 5mm core 3mm sinew....
Schould put a thicker sinew layer on it but it will push the neutral plane to the horn glue line. Especially if the horn is thin.
6mm core is good for warbows well ower 100#
But waiting for what the pro bowyers say ;)
I'd say the kiln dried wood can be part of the problem too. It is really quite a bit more brittle compared to air dried. More sinew would in any case solve it though.
On the other hand, small cracks in the core is probably quite acceptable. Peter Dekker washed off the sinew layer of a manchu original, and there was lots of little cracks along the bending sections.
Which way do you orient the growth rings in the limbs? Flat, or standing? If they are standing, it is quite difficult to know how the real fibre direction is. Flat rings are safer, as you will see the fading growth rings which should be avoided.
On the other hand, small cracks in the core is probably quite acceptable. Peter Dekker washed off the sinew layer of a manchu original, and there was lots of little cracks along the bending sections.
Which way do you orient the growth rings in the limbs? Flat, or standing? If they are standing, it is quite difficult to know how the real fibre direction is. Flat rings are safer, as you will see the fading growth rings which should be avoided.
Thanks for the advice. I was limited to the horn thickness at maximum of 4mm due to the thickness of the horns before working them so the wood thickness was kind of determined for me.....I suppose I will have to use much thicker sinew if this happens again.
The wood is all flatsawn not on the bias or quatersawn as per Adam's recommendation regarding lateral stiffness.
This problem is very frustrating because all the work and waiting has already been done.... I really want to get better at making these bows but I must be doing something consistantly wrong. As has been suggested it must be the sinew thickness or ratio of horn/wood/sinew.
The wood is all flatsawn not on the bias or quatersawn as per Adam's recommendation regarding lateral stiffness.
This problem is very frustrating because all the work and waiting has already been done.... I really want to get better at making these bows but I must be doing something consistantly wrong. As has been suggested it must be the sinew thickness or ratio of horn/wood/sinew.
I fully agree with Fusizoli: less wood and more sinew. Plus, I think that cherry could be quite brittle in tension. What was the min radius of bending?
A pity for bows Mike, i am not expert but Francesco, Kviljo and Zoltan have interesting and useful points.
I would only ask is there any exemple to use cherry for the grip for Ottoman bows or any other bow where splice is in bending part? We saw in one exemple that cornel doesn't work well.
I do experiment with other kind of bow but i use same specie of wood for the grip/splices as limbs wood species (one acer campestre, second one ash, made several raw cores but am still not satisfied so i don't dare to glue the horn and do other stuff, my budget isn't for game.
Also, there are great advices here such as your bad experiences shown here are worth learning about possible failures. I shall use equal proportion of horn/wood. And what i've learnt now is to use more sinew for security (as i remember Adam suggested it for less experienced makers as i am -3 layers).
Thank you for showing details (i know what i can expect in the future ).
Cheers and wish you luck with next attempts!
I would only ask is there any exemple to use cherry for the grip for Ottoman bows or any other bow where splice is in bending part? We saw in one exemple that cornel doesn't work well.
I do experiment with other kind of bow but i use same specie of wood for the grip/splices as limbs wood species (one acer campestre, second one ash, made several raw cores but am still not satisfied so i don't dare to glue the horn and do other stuff, my budget isn't for game.
Also, there are great advices here such as your bad experiences shown here are worth learning about possible failures. I shall use equal proportion of horn/wood. And what i've learnt now is to use more sinew for security (as i remember Adam suggested it for less experienced makers as i am -3 layers).
Thank you for showing details (i know what i can expect in the future ).
Cheers and wish you luck with next attempts!
Thank you Zoran.
I have managed to get some hornbeam that has perfect grain. It bent perfectly and has been sat on the forms for over a month now. I will be doing the splices soon.
I will be putting all the above advice to use and really concentrating on making this next bow as close to perfect as possible.
I have managed to get some hornbeam that has perfect grain. It bent perfectly and has been sat on the forms for over a month now. I will be doing the splices soon.
I will be putting all the above advice to use and really concentrating on making this next bow as close to perfect as possible.
Air dried wood are best for sure but my first bows are made by kiln dry,I do not lived any problem. I believe form and proportion of cross section are more important. 3 mm snew is too much for, 4-4 wood-horn, I think it can easy twisted.
Gluing line is very important where it placed on center line.
I believe glue absorbing of snew and backing methot are very important.
Cem
Gluing line is very important where it placed on center line.
I believe glue absorbing of snew and backing methot are very important.
Cem