String angle

[bradsmith2010]

when the bow is too heavy for you to draw,, no matter what the string angle,,  you will experience stacking

[willie]

I don't think changing ratio quite covers it all. The changing ratio of the string is a constant thing. It changes from being to your advantage to being against your advantage. As far as I know it's a constant linear change. People always talk about stack as coming up against a wall. I don't have a lot of experience with stack

Don,
you mentioned Alan's old PP thread in last years discussion.

Code: [Select]

https://www.tapatalk.com/groups/paleoplanet69529/longbow-airbow-virtual-build-along-t16569.html?sid=2e3092aaedfd5bf3ec486832c1a1efe4
Looking over Alan's graphs there, I don't see any straight (linear) lines. Which ratio are you referring to specifically?


An aside about walls.
Here is a pic of a bow that would not break, well, the "back" broke kinda strange. It had a cable back above the back you can see in the pic and the belly wood did not fail. A shear failure?

anyways, it was pulling about 75# at 22" and was definitely up against a wall.
42" ntn

[DC]

The ratio between how much the string moves and how much the tips move. I would like to see a graph of that.

[willie]

the other thread mentions each bow geometry would have it's own graph.

you could easily use one of the available programs to generate the graph by inputting the bows basic length, draw, and side profile data, without necessarily doing a complete design involving the materiel properties or solving for thickness, width or poundage.

[DC]

I need a new computer for that. I could just get a new graphics card but the computer is just getting to old. It's my birthday at the end of the month. Maybe

[Del the cat]

  I don't accept that the string angle should correlate with the handle. I have alwasy heard and it makes sense that the string angle correlates to the outer limb. 90 degrees is usually the point where stacking becomes pronounced.

+1
I'm having trouble making much sense of the explanations so far. Unless you treat the limb as a rigid lever hinged at the grip...
Hang around and I'll draw a sketch or two of how I see it !
Hope I've got it right, I never was very good with vectors... always seemed you could draw any two random lines as long as the met at 90 degrees 
I did a nice little video of a pyramid test that really shows ho you end up pulling along the limb as string angle increases:-
https://www.youtube.com/watch?v=giupEDyCdKo&t=18s

Del

[DC]

Opinion here. I don't think changing ratio quite covers it all. The changing ratio of the string is a constant thing. It changes from being to your advantage to being against your advantage. As far as I know it's a constant linear change. People always talk about stack as coming up against a wall. I don't have a lot of experience with stack as I don't make short bows(yet) so I'm going by what I've read. It seems like there may be two or more things that come together at one time to form the wall. I do know that the lever of the limb gets shorter as the limb bend gets tighter. Maybe the loss of mechanical advantage from this combined with the loss of mechanical advantage from the gear change combine.  I'm pretty sure that mechanical advantages are multiplied rather than just added so if they happen at the same times it might make the wall.  I'm quite willing to be proven wrong.

It all of a sudden occurred to me that an FDC shows the actual weight the archer feels(I can be a dolt sometimes) and any charts I've seen that show stack show a gradual increase in DW not a "wall". Has anyone got an FDC that shows a bow with serious stack?

[mmattockx]

It all of a sudden occurred to me that an FDC shows the actual weight the archer feels(I can be a dolt sometimes) and any charts I've seen that show stack show a gradual increase in DW not a "wall".

Stacking is one of those things that seems to defy a good definition or at least an agreed upon definition. When you look at FDC curves almost every bow shows some increase in the rate of weight gain per inch of draw as you get out near full draw. Yet lots of guys will say that isn't stacking, because the gain is gradual enough that the archer doesn't really notice it. I have wondered about how much change is acceptable before it could be called stacking? 5%, 10%, 20%?


Mark

[willie]

I have wondered about how much change is acceptable before it could be called stacking?

If we are settling on a definition for the sake of this discussion, I would say none. Where the curve inflects is as good as any. If folks want to characterize the stacking past that point, that's fine too.

[mmattockx]

If we are settling on a definition for the sake of this discussion, I would say none. Where the curve inflects is as good as any.

That would be my definition as well, but I have seen fairly heated discussions on other sites that some insist it isn't stacking until you can feel it while drawing the bow.

This is maybe part of my question above, how much change per inch of draw does it take for the archer to feel it? Of course, this depends on the sensitivity of the archer, but there should be some kind of general magnitude of change that most of us can notice but well before it feels like a wall has been reached.


Mark

[DC]

To get back to the original string angle is fairly straight forward in a straight bow but recurves mess with my head. I've brought this up before and got many different answers. We've got some new faces on here. What is the string angle on this bow. Just close will do.

[DC]

How about this one? Ignore the tiller. Please