Author Topic: Confusing and extreme limb twist  (Read 1053 times)

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Offline Halfbow

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Confusing and extreme limb twist
« on: August 12, 2018, 03:26:38 pm »
Hey guys, I'm a long time reader, first time poster. I've just ruined a bow trying to fix limb twist. and I think it may be interesting to discuss what happened. Maybe I'm just confused, but I think it was an unusual situation.

It was a hard maple backed jatoba board bow. A rectangular cross section narrow pyramid bow with holmeguaard style tips. Unstrung it was straight, tips were in line with the handle, and it had no meaningful twist. (Still huge tips, temporary nocks, and unshaped handle)



I got it bending to brace height, (pretty straightforward with the pyramid design), and I was dismayed to see a lot of twist in one limb.



The twist only appears when it's bent so I figured there wasn't much place for fixing it with heat. I would have to fix it with tillering. I got out my calipers to check, and they told me that the thickness was very consistent up and down both sides of the working areas on the bow. That means it's just some weirdness in the wood I used, right? It's a natural material after all.

So I had to figure out which side was the strong side and which side was the weak. Thanks to some excellent advice on this forum, I know that because the limb is bending to the right in this pic, the weak side is on the right. (Illustrated excellently in this thread http://www.primitivearcher.com/smf/index.php/topic,27206.15.html)



Except, all over this site is the advice that the strong side is the side that's farther away from the string. So the tip should rotate such that the strong side is trying to be farther from the string. The weak side should be pulled in more by the string. As you'd expect. (That is illustrated quite well in this post http://www.primitivearcher.com/smf/index.php/topic,61383.msg857869.html#msg857869) But that means on my bow, the right side (in the pic) is stronger. Quite dramatically so.



So which side was the strong side? I was getting contradictory answers based on which aspect of the twist/bend I was looking at.

Because the whole limb was bending to the side, and I cared about getting the string back in line with the handle more than I cared about fixing the rotation of the tip, I decided to take wood off the left side (in the pic).



I set up my camera on a tripod and put the bow in a position that's easy to recreate. This allowed me to take pics from exactly the same angle so I could monitor my progress.

And it worked! Sloowly, after much scraping, the limb starting moving in the right direction. Here's a gif of my sequence of images, a good amount of wood removed between each one. It's a little hard to follow the sequence because the tiller was always changing around as I scraped. Also, as the bow got weaker, the paracord I was using as string started stretching less, making the brace height comically high. Despite all this, here you can see the limb's progress in the correct direction.



Hurray! Except. I was taking off so much wood to get such a small effect. It wasn't long before I gave up on the bow and turned it in to an experiment. The 6th picture there is as far as I took it because I had gone from a stubborn stiff stick that didn't want to bend much more than brace height to a bow that was 15lbs at 32 inches, just by scraping one side. So one side of the limb remained almost a half an inch thick, while the other side was approaching a knife edge. On the side I was scraping I had gone well through all the jatoba on the belly and was just working with maple. And I was still only half way to getting the limb to where it should've been.

The limb looked like this.



Even after all that, it was only halfway fixed. So my question to you guys is, how on planet earth is this side:



Still stronger than this side:



What am I missing?

Thanks!
« Last Edit: August 13, 2018, 07:36:22 am by Halfbow »

Offline Pat B

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Re: Confusing and Extreme Limb Twist
« Reply #1 on: August 12, 2018, 04:35:41 pm »
Your belly thickness is uneven from side to side. That will cause the twist once under a strain. Do you tiller your bow clamped in a vice on the end of a work bench?
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline Halfbow

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Re: Confusing and Extreme Limb Twist
« Reply #2 on: August 12, 2018, 05:15:22 pm »
It wasn't uneven though. I checked with calipers. I was pretty anal when shaping it, and it ended up so even side to side that I legitimately surprised myself by how good of a job I'd done. Later, fixing the twist involved making the thickness (very) uneven.

Offline George Tsoukalas

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Re: Confusing and extreme limb twist
« Reply #3 on: August 12, 2018, 05:34:35 pm »
It twists towards the weak side so remove wood from the other side. Did you do that? Jawge
Set Happens!
If you ain't breakin' you ain't makin!

Offline Halfbow

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Re: Confusing and extreme limb twist
« Reply #4 on: August 12, 2018, 06:17:25 pm »
I did take wood off the stronger side, yes. Fairly confident. There's a picture pointing to the side I took wood off of up there. Perhaps it was the wrong side? I'm sure you could tell me better than I know. But it did help bring the limb in to alignment.

My main confusion lies in the fact that I took so much wood off the strong side that it was reduced to almost nothing, but still seemed to remain the strong side (though less so).
« Last Edit: August 12, 2018, 09:06:59 pm by Halfbow »

Online Mo_coon-catcher

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Re: Confusing and extreme limb twist
« Reply #5 on: August 12, 2018, 08:52:08 pm »
An easy way I do to align limb twist, remove wood from the side you want the tip to go towards. It always works fine for me with round bellied bows. Iíve never had to do it with flat bows, but Iím assuming itíll work the same.

Kyle

Offline Ryan Jacob

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Re: Confusing and extreme limb twist
« Reply #6 on: August 13, 2018, 02:14:56 am »
I see what happened, thereís a sticky about this topic somewhere. You fell into the trap of removing wood from the weak side. The side that leans toward you is weak, this causes it to bend farther. You need to remove wood from the side bending away from you since itís bending less than the other side.
You donít know desperation till youíve split a stave with screw drivers.

Offline George Tsoukalas

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Re: Confusing and extreme limb twist
« Reply #7 on: August 13, 2018, 04:43:31 am »
"Except, all over this site is the advice that the strong side is the side that's farther away from the string."

Absolutely not. It is the other way around.

Ryan is correct. You got confused. Happens to the best of us.

Weak side is farthest away from the string in a strung bow. Remove wood from the other side.

Check out 4est post, "the Mechanics of Limb Twisting Explained." He has it right.
Jawge
« Last Edit: August 13, 2018, 04:53:20 am by George Tsoukalas »
Set Happens!
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Offline upstatenybowyer

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Re: Confusing and extreme limb twist
« Reply #8 on: August 13, 2018, 04:44:53 am »
I'm no expert, but my intuition's telling me that the tree your corewood (board) was cut from had some major twist to it. The more you tillered the bow, the more it began to show itself.

Perhaps this is assumed and obvious, but in my experience you can remove wood from the "correct" side all you want, but unless you fix the twist with heat, things will never work out.
"Even as the archer loves the arrow that flies, so too he loves the bow that remains constant in his hands."

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Offline PatM

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Re: Confusing and extreme limb twist
« Reply #9 on: August 13, 2018, 05:45:22 am »
 You definitely took it off the wrong side.  The appearance of the twist decreasing is likely just your brace height increasing and hiding it.   The actual angle of the limb tip looks the same or worse.

Offline simson

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Re: Confusing and extreme limb twist
« Reply #10 on: August 13, 2018, 09:28:22 am »
You definitely took it off the wrong side.  The appearance of the twist decreasing is likely just your brace height increasing and hiding it.   The actual angle of the limb tip looks the same or worse.

+1
Simon
Bavaria, Germany

Offline Halfbow

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Re: Confusing and extreme limb twist
« Reply #11 on: August 13, 2018, 09:52:21 am »
"Except, all over this site is the advice that the strong side is the side that's farther away from the string."

Absolutely not. It is the other way around.

Ryan is correct. You got confused. Happens to the best of us.

Weak side is farthest away from the string in a strung bow. Remove wood from the other side.

I believe you misspoke here. I'm going to quote you from a couple other threads.

The bow twists towards the weak side. The weaker side is the one closest to the string in the braced bow. Strong side is furthest.

and

Like Ad said remove wood from the highest side or where the distance from string to bow is the greatest.
Weak close, strong far, same as I said. I've seen you say it several times more too that I won't bother to quote. You're always consistent about it, except here. Not trying to be argumentative, really just trying to get to the bottom of this.

It was even said here in this thread.
You fell into the trap of removing wood from the weak side. The side that leans toward you is weak, this causes it to bend farther. You need to remove wood from the side bending away from you since itís bending less than the other side.
Ryan, when you say "toward you" I take you to mean like if you're holding the bow in shooting position looking at the belly. If so, that is just another statement of weak close, strong far. Right?

And to everyone pointing me to 4est Trekker's stickied thread "The Mechanics of Limb Twisting Explained", yes, that is the first thread I linked to in my original post. I've read it and feel I understand it and it seems to support me taking wood off the side that I did.

But this is getting extra convoluted because there is contradictory advice happening here. Can anyone see what I was trying to illustrate with these pictures?


This is 4est's advice in the stickied thread. This is also the advice Mo_coon-catcher gave me in this thread. This is the advice I followed.


This is the "weak close, strong far" advice. The advice Ryan gave me in this thread (if I'm understanding you right). This is the advice I did not follow.

To be clear, both of those are the same photo.

4est's thread talks about lateral bend off of an imagined ideal center line. The "weak close, strong far" advice talks about what I would call the actual twist. Two different effects which are closely related and both usually the result of a weak side. My bow seems to be unusual in that the lateral bend and the twist are suggesting different sides are the strong side, as illustrated by those two pictures.

I'm very open to being wrong here, in fact I would welcome the clarity. This just remains my understanding. If I'm interpreting people's advice wrong in those 2 pics, I would love to know how.

If you closely watch my gif of the limbs progress, near the handle you can actually see the belly wood being reduced. Notably you can see the moment I made it all the way through the jatoba and hit maple in picture 5. Removing wood from that side is different from what 4est's thread suggests? I'm struggling to see how.

You definitely took it off the wrong side.  The appearance of the twist decreasing is likely just your brace height increasing and hiding it.   The actual angle of the limb tip looks the same or worse.

I absolutely agree that the amount the tip is rotated is the same or worse. But I'm less sure that the decrease in the lateral bend of the limb is an illusion. When bending the bow from unstrung to braced, the lateral bend of the limb increased. And it increased further the more I drew the bow. That is to say, the string became more out of line with the handle the more I drew the bow. You're suggesting that after a point, that trend would reverse? And the more the bow bent the more in line things would become? That also suggests that taking wood off the wrong side to such an extreme degree didn't make the bow worse, just because of a few inches of extra brace height? That strikes me as unlikely. The limb moving in the right direction despite the increase in brace height I took as more evidence that it was moving in the right direction. But I still have the bow, so when I get a chance I can test your theory. I can just put a longer string on it and check to see if it's insanity bad at a lower brace height.

Everyone giving me a simple "you took wood off the wrong side" has to contend with the fact that my extreme measures didn't make the limb alignment problem worse. I think it's pretty clear that there are more interesting things going on here.

I'm no expert, but my intuition's telling me that the tree your corewood (board) was cut from had some major twist to it. The more you tillered the bow, the more it began to show itself.

Perhaps this is assumed and obvious, but in my experience you can remove wood from the "correct" side all you want, but unless you fix the twist with heat, things will never work out.

This is my leading theory at the moment too. But do you fix with heat even when the unstrung bow is straight? So that would involve taking a straight stick and inducing twist?

Edit: I went ahead and tried a longer string. My suspicions were correct, the heightened brace height wasn't misleading. The bow looks more in line than ever at a lower brace height. Here's the first 'before' pic I took vs the 'after' pic I just took. You can see where I removed wood too. (Sorry, different day, different lighting)



The side I took wood off of definitely helped to bring the limb in line. So if I had taken wood off the other side, as per many suggestions here, it would have gotten more out of line. Right?
« Last Edit: August 20, 2018, 11:06:09 am by Halfbow »

Offline PatM

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Re: Confusing and extreme limb twist
« Reply #12 on: August 13, 2018, 11:19:01 am »
It actually looks like your removal has caused the limb to bend sideways substantially rather than actually twist less.

Offline Halfbow

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Re: Confusing and extreme limb twist
« Reply #13 on: August 13, 2018, 11:39:17 am »
Yes, exactly. It made it bend substantially sideways in the correct direction. The camera is in line with the far limb and the handle. The offending limb was bending laterally way to the side. Not good. Made the string not track above the handle. My corrections brought it back in line a little.

If it were perfect it would be in the red outline:
« Last Edit: August 13, 2018, 11:42:32 am by Halfbow »

Offline PatM

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Re: Confusing and extreme limb twist
« Reply #14 on: August 13, 2018, 11:44:57 am »
Yes but it did so at the expense of correcting the twist at all.  The idea is to use a straightening of the twist to rotate things into line, not just physically move the limb over.