Core broken
Hi, so my latest Turkish bow that I posted about with the lifting sinew problem actually had a broken core.
The upper limb kept acting weak, even after material was removed from the lower. I'd correct the stronger limb, string it and still the upper would be weak. I also noticed it was bending too much in one spot. I couldn't understand this as the taper was perfect. As I said in my other thread sometimes when drawing this bow I would hear a cracking noise....well at least I know what it was now!
I re-glued the sinew and it held for a while but after drawing the bow and it making cracking noises again I decided enough was enough and I couldn't shoot a hornbow that made noises! Too scary! Then I looked at the sinew and it had lifted again. At this point I thought I may have to take off the whole last sinew layer, thinking that it must have been a problem during this last layer that caused all these problems. So I filed off the offending lifting sinew and noticed while doing so that the sinew wasn't attached to the core at all in this one area.....so I pulled up the loose sinew and noticed a crack in the core wood going virtually right across the limb......It just goes to show how strong the sinew layer is at only 2 mm thick....it was holding this bow together out to a 26 inch draw....
So my question is why did the core break?
The grain was perfectly straight.
The bending process went very well with no splinters etc.
The core was left to season for over a month.
It was American Hard Maple.
The broken section was right at the kasan eye.
The first cracking noise happened during the first few tentative draws.
I want to get started on my next 'batch' of hornbows but am slightly worried by this breaking core if anybody can shed some light on why this might have happened I would be very grateful.
The upper limb kept acting weak, even after material was removed from the lower. I'd correct the stronger limb, string it and still the upper would be weak. I also noticed it was bending too much in one spot. I couldn't understand this as the taper was perfect. As I said in my other thread sometimes when drawing this bow I would hear a cracking noise....well at least I know what it was now!
I re-glued the sinew and it held for a while but after drawing the bow and it making cracking noises again I decided enough was enough and I couldn't shoot a hornbow that made noises! Too scary! Then I looked at the sinew and it had lifted again. At this point I thought I may have to take off the whole last sinew layer, thinking that it must have been a problem during this last layer that caused all these problems. So I filed off the offending lifting sinew and noticed while doing so that the sinew wasn't attached to the core at all in this one area.....so I pulled up the loose sinew and noticed a crack in the core wood going virtually right across the limb......It just goes to show how strong the sinew layer is at only 2 mm thick....it was holding this bow together out to a 26 inch draw....
So my question is why did the core break?
The grain was perfectly straight.
The bending process went very well with no splinters etc.
The core was left to season for over a month.
It was American Hard Maple.
The broken section was right at the kasan eye.
The first cracking noise happened during the first few tentative draws.
I want to get started on my next 'batch' of hornbows but am slightly worried by this breaking core if anybody can shed some light on why this might have happened I would be very grateful.
You make it sound like as if the sinew wasn't glued to the core in that spot. Maybe glue failure and a small pocket of air?
I don't know for sure if the sinew just wasn't stuck correctly in the first place which led to the core breaking or the core broke first.
I don't think the sinew layer was at fault as that is one area of hornbow making that i'm ok at and am happy with my methods.
However I have just been looking at the cross section of the limb there and I don't think I made the sinew flat enough across the back. It was flat in the center but not all the way to the edges. Now that i've removed the 'loose' sinew and have the center of the core (top of its crown) exposed I now realise that the edges of the limbs sinew was at the the same height as the top of the core. So maybe the top of the core was too 'high' in the limb proportionately and therefore was being asked to do some tension work? Obviously a core being asked to take tension forces would of course break easily. If the sinew had been flat all the way across the back then maybe the core would have then felt different forces?
I don't think the sinew layer was at fault as that is one area of hornbow making that i'm ok at and am happy with my methods.
However I have just been looking at the cross section of the limb there and I don't think I made the sinew flat enough across the back. It was flat in the center but not all the way to the edges. Now that i've removed the 'loose' sinew and have the center of the core (top of its crown) exposed I now realise that the edges of the limbs sinew was at the the same height as the top of the core. So maybe the top of the core was too 'high' in the limb proportionately and therefore was being asked to do some tension work? Obviously a core being asked to take tension forces would of course break easily. If the sinew had been flat all the way across the back then maybe the core would have then felt different forces?