Primitive Archer
Main Discussion Area => Bows => Topic started by: wizardgoat on July 18, 2015, 03:48:18 pm
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Lately I've been revisiting some earlier bows I made, putting them through my chrony and doing FD charts. I know lots of guys don't bother with this stuff, and I'm one of them, usually, but it's pretty cool to see how some bows compare to others.
Its very obvious when your shooting a sweet shooter, or a stinker, but for me seeing it visually on a graph is helpful.
ive always been told that 90 degrees is the limit, and that bad stacking will occur if you go past that.
Some of my wood bows begin to stack before 90 degrees, but othets barely stack when they're drawn more than half their length.
I've heard that horn bows can be very smooth even beyond 90 degrees as well.
string angle to me doesn't seem to give the full reason for stacking, and that materials play a huge role too. Some bows hit a wall and can't give you more, while it seems like some can just take it.
Just an observation, sorry for the ramble!
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Shorter Stiff handle bows seem to stack with very little draw.
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If you look at the geometry, beyond 90deg the limb tips are pulled back, straight through the limb instead of the limb bending to the string. Flipping the tips reduces the string angle so a longer draw is possible. Look at an Asiatic horn bow at full draw. The string angle at the tips is still under or right at 90deg, even with the longer draw.
A F/D curve should tell the tale though.
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To me the question is how do you measure string angle?
It's the angle between what and what?
If the last inch of limb flips though 90 degrees it can look like a better string angle, but it's so close to the tip it makes no difference...or does it give a slightly longer string?
Surely it depends which bit of the limb is actually bending.. what I'm saying is if you look at a bow at full draw and mark where the tip and fade are.
Assuming the limb starts out at the fade at the ame angle of deflex or reflex you could draw all sorts of weird and wonderful limb shapes that joined up those two points... but would they actually perform differently and why?
Hmmm smacks of overthink maybe...
Del
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Thats all true PAT but there's one other thing that cotrolls stack. It's when one lmb finish's be fore the other. Shorter the limbs more and stronger the stack. Use'lly thats why longer bows have less stach. It's easyer to tiller older bows than shorter ones also.
Comes down to your tillering. Pats satement about string angles 90 degress is right on. This the same princable as why bows with around 1 or 2 inch of string follows alright.
That distance seams to help with stacking.
Here's what I do when I lay the bow out. I make sure the place of my handle has 5 or 6 inchs where the limbs will be. Are also straght. From here your tillering as to make both limbs finish the same.
inng ame.
Just because you put on a straing and your frofile looks good dos'nt mean both limbs finish the same.
Most bows it you tiller to a good profile it'll be oAS YOUR TILLING GET BETTER YOUR BOWS SHOOT SMOUTHER IT SHOOTS. THE CLOSER THE LIMBS FINISH THE SAME THE BETTER YOUR BOW WILL SHOOT AGAIN SMOOTHER AND ALSO WHERE YOU LOOK WILL GET BETTER WITH TILLERING ALSO.
Bows that the limbs arn't already close the ones you have to take out deflex are prime canadates for stacking.
Putin g in reflex green makes sure the stave I start with it as even as it can get. My bows wont's stack untill I get down in the low 5o's. Then I can start feeling finger pinch. A 56" bows are perfect for me to shoot right off the ground. Closer to the ground easyer it is to camo in.
I like to gobbler hunt right off my butt with a selfbow. And shoot off milk creats most time BUCK HUNTING. But if the place is right I'll don't have a problem setting on the grond buck hunting.
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If you look at the geometry, beyond 90deg the limb tips are pulled back, straight through the limb instead of the limb bending to the string. Flipping the tips reduces the string angle so a longer draw is possible. Look at an Asiatic horn bow at full draw. The string angle at the tips is still under or right at 90deg, even with the longer draw.
A F/D curve should tell the tale though.
It's all abut string angle
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Del, my idea of string angle is where the string comes off the tip, the first inch or so. The way I see it is after 90deg the string pulls along the length of the limb instead of pulling against the bend.
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In addition to the above, whip tillered bows will also stack unless left long. Jawge
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Levers are great against stack because they reduce string angle. It's all about leverage.
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Build up the tips, easy peasy.
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JAWGE your right I forgot to add that.
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A whip tillered bow is still just an example of the string angle scenario.
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With the bows the seem to stack before the 90 degree angle, I wonder if the fibers are maxing out the amount that they will freely move before binding. I'm thinking that since the fibers are hollow tubes that we are stretching and compressing, the fibers have to move in some way. When the fibers stretch they will pull in tighter making them narrower and the belly fibers will squash down and pudge out. I'm thinking that the bows that seem to stack before 90 degrees if these tubular fibers have thicker walls that have a shorter distance they can be stretched or squashed before they bind in there movement. And it would be the same but opposite for the ones that seems to stay smooth past 90 degrees. The fiber walls might be thinner allowing more stretching or squashing effect before binding.
I have no idea if this is true or not, just a though. I hope I explained well enough for my thinking to be understood.
Kyle
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No, that's just your perception. The wood will just continue to disrupt in structure. As long as you maintain leverage advantage you can't actually "feel" that point.
That's how ignorant people break bows by overdrawing them. They aren't conditioned to the sudden failure response so they plow right through that mythical stacking wall.
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Here's what CROOKETARROW told me. When stacks becomes notesable when you draw the more and father you draw, the more you run out of bending wood the more stack you get.
Shorter bows have less wood to bend. Quicker to 90% and more stack.
This exsplane's why longer bows have less stack. They have more limb with bendy wood.
Better tiller more bendy wood less stack
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Look at the bigger picture.
Angle in the string where you pull from and the angle at the tips are both important factors.
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Here's my hypothetical bow.
Its drawn perfectly symmetrically except one limb is shaped slightly differently over the last few inches, but the nock position at brace and full draw is identical (btw it shoots real smooth ::)).
Is the string angle actually any different for each limb assuming the limbs flex over the same length?
Is the string angle the actual tip angle or the angle from string to a point midway down the limb?
Note the angle of string at the fingers is the same either side (assuming bow held dead centre, arrow shoots from dead centre for simplicity)
Del
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@Del....ya gotta huge hinge on the left limb of your bow. :laugh:
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"Is the string angle the actual tip angle or the angle from string to a point midway down the limb?"
Tip angle.
Jawge
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Del, you can see that you can't draw an ellipse and put a recurve on one side. The increased bend on the recurved side would change the whole limb. That's why you had to throw the hinge in there to get everything lined up
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So in Del's picture the right limb would stack before the left?
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OK...
So if we now assume both limbs are totally static for the last section (up to and including the hinge) as shown in the new pic'.
They both now have identical 'working limb' length.
Does the silly shaped lever behave any different to the slightly deflexed shaped lever?
Is the actual string angles the same on each?
I'm playing Devil's advocate to some extent here... As PatM points out if I add the recurve without the hinge (dotted line) I'm increasing string length, which changes the geometry . I'm just striving for better understanding of cause and effect really.
Del
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"So in Del's picture the right limb would stack before the left?"
Correct.
All bows stack potentially, Del, the limb on the right would, way before the one on the left.
You lost me on the rest of your last post LOL. Spent a good part of the day in 90 deg F temps.
Jawge
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I think stack is really just simple geometry. the tip moves in an arc--and has a backward component and a downward component. Only the backward component results in forward arrow movement. After 90 degrees, the percentage of downward motion is greater than the backward motion and stack begins to limit how much further the bow can be drawn. Since our draw is only backward, you reach a point when it is no longer possible to to draw. on an infinitely bendable limb, that would be when the tips point straight back. recurved tips delay that point.
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Yup.
Geometry. 90 degrees is the magic number. When the string angle gets there, that's it for drawing the bow.
Jawge