Problem in bending bamboo
Greetings,dear all.
I am a green hand in hornbow making and never have I known that it is so hard a job.
Days ago,I bent bamboo pieces to C shape and only to find nearly every bamboo cores except one has a break along the bamboo.I can see clearly that the breaks happened where the cores were bent the most-----inside part of the cores.
What can the problem be?..............I cut away half of the bamboo and let it be 80 cm long,4cm wide and 0.5 cm thick. Then I put the core in a thermos bottle for 5 minues,and bent it when it was hot.At last I strung the bamboo piece with a rope to keep the bend(the core was still very good at this time) and strengthened the bend over burning alcohol..............the core broke at the time.
Do the breaks matter?can anyone tell me how to avoid the problem
or if I should ignore the problem?
------Wu Kai
I am a green hand in hornbow making and never have I known that it is so hard a job.
Days ago,I bent bamboo pieces to C shape and only to find nearly every bamboo cores except one has a break along the bamboo.I can see clearly that the breaks happened where the cores were bent the most-----inside part of the cores.
What can the problem be?..............I cut away half of the bamboo and let it be 80 cm long,4cm wide and 0.5 cm thick. Then I put the core in a thermos bottle for 5 minues,and bent it when it was hot.At last I strung the bamboo piece with a rope to keep the bend(the core was still very good at this time) and strengthened the bend over burning alcohol..............the core broke at the time.
Do the breaks matter?can anyone tell me how to avoid the problem
or if I should ignore the problem?
------Wu Kai
Never having tried this degree of bend, I would hazard a guess that maybe it is too great an amount in one go? Maybe try to achieve the bend you want over several stages?
I think that a physical effect known as the 'poisson effect' causes stress along the bamboo at the same time that that you are bending it. Perhaps the species and the age of your bamboo is contributing to the problem.
Old Chinese bows that I have cut up frequently show splitting in the core that occurred during manufacture (which I know because the glue has filled the cracks. So it may be that it doesn't matter so much.
Expert bowyers will be able to advise better.
Old Chinese bows that I have cut up frequently show splitting in the core that occurred during manufacture (which I know because the glue has filled the cracks. So it may be that it doesn't matter so much.
Expert bowyers will be able to advise better.
Thank you ! You two are really unselfish to share your experience with me.
The splits are not too deep or long---only about 1 to 3cm,and they are in the middle way between the tip and the handle.
I will take Stephen's advice and go on with my first hornbows.I need make two ,maybe three bows,since I need more than a year to check whether I can succeed at last.
The splits are not too deep or long---only about 1 to 3cm,and they are in the middle way between the tip and the handle.
I will take Stephen's advice and go on with my first hornbows.I need make two ,maybe three bows,since I need more than a year to check whether I can succeed at last.
From my (limited - only three bamboo bows) experience, for good bending, bamboo has to be green and the temprature should be in excess of 200 deg. Once it begins to "sweat" (small droplets of sap appear on the shiny side), it becomes soft enough for bending.
The causes of cracking are correectly described by Stephen: bending with the shiny side out causes the edges to lift up (Poisson) which puts the inner side under crosswise tension. Small cracks should not cause any problems, although it is safer to fill the cracks with glue/sinew later when the bow is backed.
Adam
The causes of cracking are correectly described by Stephen: bending with the shiny side out causes the edges to lift up (Poisson) which puts the inner side under crosswise tension. Small cracks should not cause any problems, although it is safer to fill the cracks with glue/sinew later when the bow is backed.
Adam
Thank you,Adam
My bamboo was green but didn't sweat at all,because it was mainly softened in hot water.At last ,the water was yellow.Fire was only used to strenthen the bend.
Adam,if I want my bow to be 110cm long and my core is 80 cm(40cm long when bent),how long is my siyah?
-----------------Wu Kai
My bamboo was green but didn't sweat at all,because it was mainly softened in hot water.At last ,the water was yellow.Fire was only used to strenthen the bend.
Adam,if I want my bow to be 110cm long and my core is 80 cm(40cm long when bent),how long is my siyah?
-----------------Wu Kai
110cm between nocks is a short bow. It means the draw length should rather be short too, unless you do not mind stacking.
I suggest to decide on a 120cm bow and follow the Korean design. The siyahs would then be 20cm each - about half of that would then be the tip and the rest an extension of limb. You will need this length, 20cm, plus the splice length of about 7-10cm.
Adam
I suggest to decide on a 120cm bow and follow the Korean design. The siyahs would then be 20cm each - about half of that would then be the tip and the rest an extension of limb. You will need this length, 20cm, plus the splice length of about 7-10cm.
Adam
I am short too----160cm,but I will accept your good advice.
Many thanks! :lol:
Many thanks! :lol:
I?ve had the same problem, till I began to study the making of fishing rods made of bamboo. A very very interesting job, I?ve learned a lot of that.
Never try to water or to steam bamboo for bending, I use dry heat at the back of the bamboo. Heat from the belly- side causes the cracks, it is right these cracks aren?t a problem to much, the belly is the compression-side of the bow.
Never try to make the whole bend at one time, make it in several runs.
Michael
Never try to water or to steam bamboo for bending, I use dry heat at the back of the bamboo. Heat from the belly- side causes the cracks, it is right these cracks aren?t a problem to much, the belly is the compression-side of the bow.
Never try to make the whole bend at one time, make it in several runs.
Michael
Redhawk
I am really interested in your dry heat method.Can you introduce more about it?
I am really interested in your dry heat method.Can you introduce more about it?
Sorry for my late reply.
First of all I make a strong enough negative pattern of the desired bow of hardwood. I make this negative patterns for every new bow I do, it works very fine for to bend wood, horn or bamboo, for to fix the strips of wood, horn or bamboo for to work them with knives or rasps.... for to check and recheck the bends and curves, the straight line.......
Then I work the bamboo to the desired dimensions and fix it with little pressures by using clamps for 2-3 days at the negative pattern, without any heat- treating. Then I use dry heat from the back-side of the bamboo, till the bamboo starts to be so hot that you will almost burn your fingers when you touch it, I guess this will be at about 60 degrees celsius.
A heatgun with 300 degrees celsius will do a good job.
Now enforce the pressure of the clamps. Repeat the same procedure after another 2-3 days, while enforcing the pressure of the clamp till the bamboo- strip fits exactly to the negative pattern of the desired bow. Let it be for another 2- 3 days.
You can repeat this procedure till you have the desired shape.
This method works well for me, never use to much heat or to much pressure at one time.
For to glue the bamboo you have to undercoat it with a very thin glue-solution several times cause bamboo is very hard and solid.
Michael
First of all I make a strong enough negative pattern of the desired bow of hardwood. I make this negative patterns for every new bow I do, it works very fine for to bend wood, horn or bamboo, for to fix the strips of wood, horn or bamboo for to work them with knives or rasps.... for to check and recheck the bends and curves, the straight line.......
Then I work the bamboo to the desired dimensions and fix it with little pressures by using clamps for 2-3 days at the negative pattern, without any heat- treating. Then I use dry heat from the back-side of the bamboo, till the bamboo starts to be so hot that you will almost burn your fingers when you touch it, I guess this will be at about 60 degrees celsius.
A heatgun with 300 degrees celsius will do a good job.
Now enforce the pressure of the clamps. Repeat the same procedure after another 2-3 days, while enforcing the pressure of the clamp till the bamboo- strip fits exactly to the negative pattern of the desired bow. Let it be for another 2- 3 days.
You can repeat this procedure till you have the desired shape.
This method works well for me, never use to much heat or to much pressure at one time.
For to glue the bamboo you have to undercoat it with a very thin glue-solution several times cause bamboo is very hard and solid.
Michael
EXCELLENT THREAD GENTLMEN!
Excellent for me anyway :) I just happen to be about to back a 45 year old static tip hickory recurve with bamboo some time over the next week. I've been reading these posts carefully and will basically, follow the same directions for bending/heating the bamboo to follow the recurved bow tips. I plan to sand down the bamboo, sand the back of the hickory bow (60 grt paper), make a hard wood recurve form (when I get to this point, I'll re-read your posts to figure when I should or shouldn't heat), bend the ends, glue, clamp and tiller. Voila :!:
Never backed a bow with anything but cloth before. Who knows? maybe this will be the biggining of horn, wood and sinew bow building? I hear that get contagious :wink:
Thanks guys!
J.
Excellent for me anyway :) I just happen to be about to back a 45 year old static tip hickory recurve with bamboo some time over the next week. I've been reading these posts carefully and will basically, follow the same directions for bending/heating the bamboo to follow the recurved bow tips. I plan to sand down the bamboo, sand the back of the hickory bow (60 grt paper), make a hard wood recurve form (when I get to this point, I'll re-read your posts to figure when I should or shouldn't heat), bend the ends, glue, clamp and tiller. Voila :!:
Never backed a bow with anything but cloth before. Who knows? maybe this will be the biggining of horn, wood and sinew bow building? I hear that get contagious :wink:
Thanks guys!
J.
Thank you.It must be helpful when I bend a new core or a finished bow.
Last week I ran out of bamboo logs to use for bows shaped like assyrian, turkish, and korean bows. It is made by pure laminates of bamboo only, and it keeps it's shape. So I started to make small korean bows about 18" long.
I figured out that because I cannot buy horn in my city, the piece of the outside shell of the bamboo will be enough like the koryo bow. To prevent breaking the bamboo, cut the outside shell and be careful so that the shell will be evenly measured. Use the remaining bamboo not the shell to make your curves. Boiling bamboo will just shrink the bamboo after drying nor steaming. I advice you to use direct heat from burning coal to achieve your bend. Bamboo can only bend some 60 degrees. after achieving the bend, attach the shell once again to the bamboo piece. Glue it using super adhesives such as epoxy glue. This will strengthen the bamboo because of the loss of strength during bending. do not clamp it, rather tie it, it's primitive yet very effective.
I hope this helps, I will soon post my pictures of the bows on Atarn later. Once I get my camera from my sister whose in another city for 3 weeks. Bye
I figured out that because I cannot buy horn in my city, the piece of the outside shell of the bamboo will be enough like the koryo bow. To prevent breaking the bamboo, cut the outside shell and be careful so that the shell will be evenly measured. Use the remaining bamboo not the shell to make your curves. Boiling bamboo will just shrink the bamboo after drying nor steaming. I advice you to use direct heat from burning coal to achieve your bend. Bamboo can only bend some 60 degrees. after achieving the bend, attach the shell once again to the bamboo piece. Glue it using super adhesives such as epoxy glue. This will strengthen the bamboo because of the loss of strength during bending. do not clamp it, rather tie it, it's primitive yet very effective.
I hope this helps, I will soon post my pictures of the bows on Atarn later. Once I get my camera from my sister whose in another city for 3 weeks. Bye
If you use a green piece, wet heat is best used.
It is same for wood, steaming or boiling wet wood works best.
Dry bamboo is best bent with dry heat, it does weird things when you try bend with the steam, unless you rehydrate the bamboo in water for a while.
I see many people are having trouble with the core making of the bow.
You want to have a fairly flat piece of bamboo from the start, this is easiest.
The Poisson effect is the reason why.
After you bend the bamboo to shape, do not further heat it. You can easily re-adjust bend after it is dry. Reason why you should not correct it (while it is still wet) is because this can cause one section to heat up more quickly and the stress in the core will bend this area faster than the cooler areas causing it to crack.
It is same for wood, steaming or boiling wet wood works best.
Dry bamboo is best bent with dry heat, it does weird things when you try bend with the steam, unless you rehydrate the bamboo in water for a while.
I see many people are having trouble with the core making of the bow.
You want to have a fairly flat piece of bamboo from the start, this is easiest.
The Poisson effect is the reason why.
After you bend the bamboo to shape, do not further heat it. You can easily re-adjust bend after it is dry. Reason why you should not correct it (while it is still wet) is because this can cause one section to heat up more quickly and the stress in the core will bend this area faster than the cooler areas causing it to crack.
If it is helpful, I note that Chinese bowyers started off from a culm ('log') of bamboo at least 4 inches (10cm) in diameter. Their basic core is started from one quarter of the culm, split lengthways with a simple axe.
I have also learned that even when you have selected a species of bamboo, that does not guarantee that each piece is suitable for a bow core. Different growing conditions (for example growing always in the shade or with frequent exposure to sunlight) affects the performance. Some comments in ancient classical Chinese texts suggest that the stiffness of bamboo on one side could vary significantly depending on its exposure to sunlight on that side before cutting.
A Malyasian villager has taught me that resistance to insect attack varies between different culms cut from the same stand of bamboo and has to be tested (by burial throughout one rainy season) if the bow is to be used in a place where insect attack is a problem.
This is an indication that the art of selection of material was an important element of technique in traditional bowmaking.
S
I have also learned that even when you have selected a species of bamboo, that does not guarantee that each piece is suitable for a bow core. Different growing conditions (for example growing always in the shade or with frequent exposure to sunlight) affects the performance. Some comments in ancient classical Chinese texts suggest that the stiffness of bamboo on one side could vary significantly depending on its exposure to sunlight on that side before cutting.
A Malyasian villager has taught me that resistance to insect attack varies between different culms cut from the same stand of bamboo and has to be tested (by burial throughout one rainy season) if the bow is to be used in a place where insect attack is a problem.
This is an indication that the art of selection of material was an important element of technique in traditional bowmaking.
S
by burial throughout one rainy season
i am read some article, in china burial mulberry it some time for make a wood bow, the qin(a seven-stringed plucked) wood also burial some times, this step called kill life(断阳），the wood after burial got more stability, at least use the wood dry many years, it sound liquidly, a good bow and wood also sound liquidly, more help maybe from craftsman of make the musical instrument.
some trouble of lifeing in city, difficulty find a place burial wood or bamboo,how deep and what soil are right? split bamboo/wood or original size? any possibility put the wood and soil in a big receptacle add water but the temperature ?
i am read some article, in china burial mulberry it some time for make a wood bow, the qin(a seven-stringed plucked) wood also burial some times, this step called kill life(断阳），the wood after burial got more stability, at least use the wood dry many years, it sound liquidly, a good bow and wood also sound liquidly, more help maybe from craftsman of make the musical instrument.
some trouble of lifeing in city, difficulty find a place burial wood or bamboo,how deep and what soil are right? split bamboo/wood or original size? any possibility put the wood and soil in a big receptacle add water but the temperature ?
Jiao,
This method was used in a warm, humid tropical climate. It may not be necessary in a cold, dry climate like North China. Also, because I do not have direct knowledge, I can't tell whether burying the wood puts something into the wood from the soil or takes something out.
My wife puts green mud on her face at night because she says it takes impurities out. :lol:
S
This method was used in a warm, humid tropical climate. It may not be necessary in a cold, dry climate like North China. Also, because I do not have direct knowledge, I can't tell whether burying the wood puts something into the wood from the soil or takes something out.
My wife puts green mud on her face at night because she says it takes impurities out. :lol:
S