String alignment problem
Hi!
I worked on bracing a bow today and I am happy that it didn't blow. The limbs are also balanced alright, but the string is unfortunately not centered. It is about 2cm off the middle in the grip. I attached pictures. I am unsure how to correct this because I don't know what the problem is. Any advice is much appreciated!
First, a picture of the unbraced shape. The forum won't let me attach, so I'll give the links. This bow is meant for me to learn, it is not a specific design. The bow still taught me a few important things on its way to brace. First thing was to pay attention not to shift parts when clamping to get a symmetric grip...
http://itp.tugraz.at/~skerm/Bilder/unbraced.jpg
Here it is on the pegboard. I bent it with tepeliks and over the knees first and then worked towards brace height on the board. It was really hard to bend, I wonder what it is going to draw! Hopefully I'll be able to draw it, the string tension is actually intimidating. (I didn't use the heat gun, but I admit considering it)
http://itp.tugraz.at/~skerm/Bilder/pegboard.jpg
This is with the string, no more pegs holding the bow.
http://itp.tugraz.at/~skerm/Bilder/braced.jpg
However, the string does not line up with the grip. (please disregard the dirty workshop, I recently moved in there and there is still a lot of work to do)
http://itp.tugraz.at/~skerm/Bilder/string.jpg
The braced limbs look like this:
http://itp.tugraz.at/~skerm/Bilder/twist.jpg
http://itp.tugraz.at/~skerm/Bilder/twist2.jpg
I tried to take pictures from reasonable angles. It looks like the limbs are angling away from the grip, but unbraced everything is aligned well.
Daniel
I worked on bracing a bow today and I am happy that it didn't blow. The limbs are also balanced alright, but the string is unfortunately not centered. It is about 2cm off the middle in the grip. I attached pictures. I am unsure how to correct this because I don't know what the problem is. Any advice is much appreciated!
First, a picture of the unbraced shape. The forum won't let me attach, so I'll give the links. This bow is meant for me to learn, it is not a specific design. The bow still taught me a few important things on its way to brace. First thing was to pay attention not to shift parts when clamping to get a symmetric grip...
http://itp.tugraz.at/~skerm/Bilder/unbraced.jpg
Here it is on the pegboard. I bent it with tepeliks and over the knees first and then worked towards brace height on the board. It was really hard to bend, I wonder what it is going to draw! Hopefully I'll be able to draw it, the string tension is actually intimidating. (I didn't use the heat gun, but I admit considering it)
http://itp.tugraz.at/~skerm/Bilder/pegboard.jpg
This is with the string, no more pegs holding the bow.
http://itp.tugraz.at/~skerm/Bilder/braced.jpg
However, the string does not line up with the grip. (please disregard the dirty workshop, I recently moved in there and there is still a lot of work to do)
http://itp.tugraz.at/~skerm/Bilder/string.jpg
The braced limbs look like this:
http://itp.tugraz.at/~skerm/Bilder/twist.jpg
http://itp.tugraz.at/~skerm/Bilder/twist2.jpg
I tried to take pictures from reasonable angles. It looks like the limbs are angling away from the grip, but unbraced everything is aligned well.
Daniel
Daniel, first congratulation . Good look "like Korean " bow. And you have problem maybe litlle more , but same like other Korean bows.
First - DONT USE HEAT GUN ! Mi experience is -only elektric cooking stove. I meat this problems vith mi Korean Hornbow last year too. Here in Atarn we discuss about this. Arms in Korean bows are very unstabil and you must working vith heat stove very much . if you good heating arms , dont be afraid "game " vith. Arms in mi bow if i dont string him long time, exercise like crazy horse in every angel what you can imagine !I dont meat vith this , before in mi ( less reflexed) bows. In other hand - somthing like your string position is good for Koreans right shooting vith thumbrings. Korean archer exercise vith his bow and heat and endid in this position , wher string good tuchit in siahs bridges and not centered in handle , but litlle right. Good heat working .
First - DONT USE HEAT GUN ! Mi experience is -only elektric cooking stove. I meat this problems vith mi Korean Hornbow last year too. Here in Atarn we discuss about this. Arms in Korean bows are very unstabil and you must working vith heat stove very much . if you good heating arms , dont be afraid "game " vith. Arms in mi bow if i dont string him long time, exercise like crazy horse in every angel what you can imagine !I dont meat vith this , before in mi ( less reflexed) bows. In other hand - somthing like your string position is good for Koreans right shooting vith thumbrings. Korean archer exercise vith his bow and heat and endid in this position , wher string good tuchit in siahs bridges and not centered in handle , but litlle right. Good heat working .
Dusan, thanks, but this is just a prototype meant for me to learn. I did not intend to replicate a historic bow. It's not even a real hornbow as I used epoxy to glue the horn. I guess that is a bit of a faux pas here, but it'll do for learning the mechanics. Anyway, when looking at from the side that puts the string left of the grip, I scraped the right side of each limb a bit and repeatedly bent and held the limbs to the right. I did this by fixing the grip in a vice, holding the bow by the ears and then pulling both limbs sideways. I know this procedure works for wood bows, so I hoped it would work here as well. So far it did, the string is already closer to the center. I left it braced to see if it will stay that way.
Brace height is currently about 4" from the belly of the grip, which gives a distance of about 7" at the limb centers due to the setback of the grip. I think I'll have to increase the brace height or I'll slap the wrist with the string.
I also pulled the bow a bit and I'm afraid it turned stronger than I wanted it. It draws 21# at 9" (measured from the back of the bow), although it is only 12mm thick at the limb centers. At least now I know why I got sore tricepses from bracing it.
Brace height is currently about 4" from the belly of the grip, which gives a distance of about 7" at the limb centers due to the setback of the grip. I think I'll have to increase the brace height or I'll slap the wrist with the string.
I also pulled the bow a bit and I'm afraid it turned stronger than I wanted it. It draws 21# at 9" (measured from the back of the bow), although it is only 12mm thick at the limb centers. At least now I know why I got sore tricepses from bracing it.
Ou, ou, epoxy is no friendly vith heat stove. Anyway -good work Daniel.
Actually many types of Epoxy can be manipulated with heat. Many guys remove limb twist in old bows glued with Epoxy by heating the limb (usually with hot water) and twisting the limb into a slightly over corrected position and letting it cool.
This specific epoxy starts to fail at around 60?C when it is cured at room temperature. When it is heated to 60?C for 10h after curing, it can take up to 140?C. Since I applied the sinew first on this bow, I heat treated it at 40?C, so it should take more than 60?C. But I read that sinew is damaged at 60?C (when it is wet?), so I must be careful with heat.
I havent any experiences vith epoxi heating, but you are right- be very carefull vith preheating sinew.
Good advice with the heating. Since scraping and pulling the tips in the opposite direction of the string deviation worked, I fixated the tips in the position using a jig and carefully heated both limbs equally, then left it for 1 1/2 hours. I think this finally solved the problem, the string position is good now.
Now I can proceed with making the next mistakes. :roll:
Now I can proceed with making the next mistakes. :roll:
Congratulation. Interesting that epoxy work vith this technik too.
The epoxy won't change, so it is only the deformation that is introduced in the horn and perhaps also a bit in the wood. A part of this deformation is time-dependent and will disappear after while, just like the string follow does after unbracing.
In my case, the string is now 10mm off the center again, but it was worse before. I hope it stays there.
In my case, the string is now 10mm off the center again, but it was worse before. I hope it stays there.
All epoxies will soften with heat like hide glue.
The temperature is epoxy dependent. (I do not know if it is typically low enough for these purposes or if the wood or at least sinew will suffer before. )
The temperature is epoxy dependent. (I do not know if it is typically low enough for these purposes or if the wood or at least sinew will suffer before. )
It does soften, but there is still a fundamental difference between epoxy and hide glue. The curing of epoxy is irreversible. The atoms that bond together during curing will stay bonded until the epoxy is destroyed. In hide glue, warming can release bonds and new bonds can form upon cooling. This allows the glue to adjust after heat corrections, while the epoxy would have to remain strained.
I have shot a few arrows at half draw, works fine as far as I can tell. I caught myself closing my eyes upon releasing, perhaps I am still a bit scared of the bow?
Now there is another problem. Last time I braced and drew the bow, the limbs were perfectly balanced. I measure the distance between the string and the limb on each limb to judge this. I braced it today and the limbs were not balanced, there was a difference in string distance of 1.5cm. It cannot be corrected by pushing the string towards the weaker limb. Why does this happen? I kept the bow away from the sun, there should have been no uneven temperature while storing it unbraced.
What can I do about it? Heat the stronger limb a bit while braced? I don't want to scrape more because I am afraid I will end up scraping forever.
Now there is another problem. Last time I braced and drew the bow, the limbs were perfectly balanced. I measure the distance between the string and the limb on each limb to judge this. I braced it today and the limbs were not balanced, there was a difference in string distance of 1.5cm. It cannot be corrected by pushing the string towards the weaker limb. Why does this happen? I kept the bow away from the sun, there should have been no uneven temperature while storing it unbraced.
What can I do about it? Heat the stronger limb a bit while braced? I don't want to scrape more because I am afraid I will end up scraping forever.
Have you tried bending the stronger limb over your knee and holding it over bent for some time and then seeing if the bow is corrected? Do this in the first 30 seconds after bracing.
Yes, I tried that. I left it longer with a barshak, too. I have no idea why this unbalance occured, but in the meantime I found that this time it was not a temporary thing because it stayed that way. Actually it got a bit worse after shooting about 200 arrows this weekend. I will apply some sinew to fix it.
I am very happy with the bow, I enjoyed the shooting alot!
I am very happy with the bow, I enjoyed the shooting alot!
Hi Daniel, nice looking bow, I made a bow with a similar amount of string missalignment a few years ago, i couldnt adjust it so I left it and it didnt really affect how it shot, it still shot straight, I put the string off centre the same side as the arrow sits and it shot like a centre shot and would shoot arrows of much too high spine because they didnt have to bend much around the bow. Maybe yours will still be ok!!!
Well done bow, Daniel
I do every bow with a not centered string alignment. The intention is to place the string a bit more to the left or to the right side of the grip, it depends on the needs of the archer.
As always: if you don?t let your backing enough time to dry, you?ll have those tiller problems. Polymerisation needs time, it is still working within your bow.
Don?t try to correct the tiller right now, leave the bow for some more weaks alone. Otherwise yo??ll end up with a lame duck.
Michael
I do every bow with a not centered string alignment. The intention is to place the string a bit more to the left or to the right side of the grip, it depends on the needs of the archer.
As always: if you don?t let your backing enough time to dry, you?ll have those tiller problems. Polymerisation needs time, it is still working within your bow.
Don?t try to correct the tiller right now, leave the bow for some more weaks alone. Otherwise yo??ll end up with a lame duck.
Michael
I'm not quite sure if this kind of twist will make the bow centershot. The string will always travel towards the center of the grip. If the bow is twisted like this, the grip will only be slightly twisted in the hand. The string will still travel towards the center of the grip. You are going to have to have a really strong hand to be able to hold the grip of such a bow straight for it to shoot like a centershot bow. A death grip times two might do it, but that would probably interfere with trying to get a clean loose.
Really nice bow though! Hoping to be able to make something similar myself, some day.
Really nice bow though! Hoping to be able to make something similar myself, some day.
Thanks everyone!
Some of the alignment correction went out again but I didn't notice any unpleasant torque upon drawing and it shot fine. Maybe I'll notice some problems when I become a better archer. I covered the back and the sides with parchment and I am currently painting it. Or rather I am trying to and I am not really getting anywhere.
In any case, the first craving for a composite bow is sated, now I can happily build and wait for polymerization.
Some of the alignment correction went out again but I didn't notice any unpleasant torque upon drawing and it shot fine. Maybe I'll notice some problems when I become a better archer. I covered the back and the sides with parchment and I am currently painting it. Or rather I am trying to and I am not really getting anywhere.
In any case, the first craving for a composite bow is sated, now I can happily build and wait for polymerization.
Kviljo, I think the string will travel towards the position it rests at brace height not the centre of the bow, therefore even though the string is off centre you will not experiene any twisting force upon drawing and the bow may still shoot nicely !!!!