Stack weight

[Badger]

That blows my understanding of stack weight.

  Stack weight is the same as any kind of weight, it just falls off quicker.

[scp]

My common sense says that if I keep on pulling on the stacking bow, I will be crushing the belly wood fibers by and by. Unless you are going for the flight bow record, you are better off scraping the belly to make the bow less stacking. As always, all depends on what you are trying to do with the bow. As PatM implied, horns are quite more resilient than wood.

[bradsmith2010]

 

[Stick Bender]

Stack is a interesting topic to me sense I have a long draw & make short bows these days & Patm made a interesting point about how much of the limb is still working past stack , but I have found that my peak performance (fps) comes right at the point of stack finger release it could be different with a shooting machine , I think when string angle becomes exsesive transfer energy drops quickly , I think a non stackicking 45lb bow would out perform a stacking 47lb bow finger release, but a lot depends on material used & design , but performance doesent always equate to shootability in the bows I have built I find the ones with a larger margine between full draw & stack are more user friendly !

[StickMark]

The 2.3 rule for bow length to draw length is making sense.

[sleek]

Here is the hard truth about stack weight. It has absolutely NOTHING to do with the compression of wood or anything else related to the bows stress. It has absolutely EVERYTHING to do with the angle. It's a function of leverage and ANY stacking bow can be made to not stack simply by adding recurves. Stack is actually a good thing when shooting lightweight arrows as they can benefit from the very quick dry fire like speeds of a stacked bow in the early inches of release. This is especially true if the bow has low string tension at brace, as up to half the draw weight can take place in the last few inches of draw.


I'm pretty confident on this, but not beyond being corrected if someone knows better than me.

[SLIMBOB]

PatM...primarily, I would say yes.  But I would also say that it is based in an intuitive sense.  It would seem me that 5 lbs of stack weight would not deliver the same cast or kinetic energy that 3 lbs of ....better leveraged draw weight, at the same drawn distance with the same arrow.  I can see that using a very light arrow might enable you to make better use of stack weight, but the energy stored is less.  I would think.
  It should read 5 lbs of stack weight vs 5 lbs of better leveraged weight.

  As to the Turkish bows, my assumption would be that it has more to do with string travel than anything else.

[Badger]

Sleek,you are correct. Once you go past 90 degrees you start loosing too much leverage.  Recurves will also stack but you do pick up some draw length before that happens.

[sleek]

PatM...primarily, I would say yes.  But I would also say that it is based in an intuitive sense.  It would seem me that 5 lbs of stack weight would not deliver the same cast or kinetic energy that 3 lbs of ....better leveraged draw weight, at the same drawn distance with the same arrow.  I can see that using a very light arrow might enable you to make better use of stack weight, but the energy stored is less.  I would think.

5 pounds of energy in an inch of draw is 5 pounds of energy in an inch. It is what is is it could be said. The difference between that 5 pounds being at the end of the draw stroke and it being at the beginning is this: The 5 pounds at the beginning allows all the rest of the draw stroke weight to be built up on top of it ( added up ) allowing  for a fatter FD curve and therefore higher energy storage of the bow through the power stroke. That 5 pounds at the end makes the draw curve more anorexic however allows a higher speed of string release, which a light arrow WILL benefit from greatly over a heavier arrow. The heavier arrow can not accelerate due to its mass as quickly as the light arrow, and wont be able to take ad9of that high early energy upon release.

It's similar to a heavy high hp car on the drag strip spinning its wheels, unable to move as fast as its wheels want to go because it's too heavy to accelerate that quickly, vs a rice burner just taking off because its light enough to allow its wheels to push it. It's not the best comparison due to the fact that a heavy high hp car would match its power to its wheel size and throttle etc on take off, but you get the idea.

[sleek]

Sleek,you are correct. Once you go past 90 degrees you start loosing too much leverage.  Recurves will also stack but you do pick up some draw length before that happens.

Recurves can be designed to stack or not stack, if I'm not mistaking Steve? Also, If the wood could take the load, you could make a bow bend until the limbs touched each other and not stack with the right recurves. I wouldn't suggest trying that however it would be a fun novelty... Darn it... now I wanna make one.

[PatM]

The Indian Crab bows actually are drawn until the limbs start closing in on each other.

[Badger]

 Slimbob, it is not really the stack weight that might help a light arrow, it is the designs used on the bow that have a tendency to stack. The stack itself doesn't help anything.

If a bow stacked for 2" and you broke it down into 1/4" increments it might look like this   42 43 44 45 46.125 47.250 48.375 49.5  7.6 ft # Now if you took a bow with a smoother draw it might read       45- 45.625-46.125-46.750-47.375-48-48.625-49.375=8.84 ft # energy. Not really all that much difference but you can see that it starts higher on the non stacking bow so a lot more energy is lost up front on the stacking bow.

[sleek]

The Indian Crab bows actually are drawn until the limbs start closing in on each other.

FASSSSCINATING.... I did not know this.

[sleek]

Slimbob, it is not really the stack weight that might help a light arrow, it is the designs used on the bow that have a tendency to stack. The stack itself doesn't help anything.

If a bow stacked for 2" and you broke it down into 1/4" increments it might look like this   42 43 44 45 46.125 47.250 48.375 49.5  7.6 ft # Now if you took a bow with a smoother draw it might read       45- 45.625-46.125-46.750-47.375-48-48.625-49.375=8.84 ft # energy. Not really all that much difference but you can see that it starts higher on the non stacking bow so a lot more energy is lost up front on the stacking bow.

Interesting though on the idea of it being the design of the bow that causes stacking vs the stacking being part of the design. It does seem we are in agreement however about where the weight gain happens in the draw being a most important factor in how useful the weight gain is?

[nabiul]

I wish people would call it string tip angle instead of string angle, the latter of which makes no sense at all since it leads newbies to believe it is the angle of the string at the fingers. I was wracking my brain trying to figure out why the math behind what the TBB said wasn't making sense; when you plot the inverse of cosine of half the angle at the finger tips you see a clear hyperbolic graph that shows the mechanical advantage of string tension is highest at brace and gradually lowers as you draw, but nothing that would indicate a sudden increase in draw weight at any point. I had to go back and re-read the TBB carefully to see that it was the angle of the string relative to the limb tips that they were talking about.