Primitive Archer
Main Discussion Area => Bows => Topic started by: upstatenybowyer on December 31, 2016, 08:52:34 pm
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Could an experienced member remind me why/how too much reflex can be a problem? Do woods with higher elasticities handle it better? I know I've read about this, but I'm having trouble putting it all together. Thanks
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hard to tiller- often these bows come in under weight because you have to remove so much wood to get it to brace
hard to get to brace. bow wants to turn in the hand/ on the tillering tree.
Unstable- in other words, when it's braced, one limb may want to straighten out.
Wood is more stressed than a straight bow.
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With too much reflex you over strain the bow just getting it to brace and overly reflexed bows are hard to brace without it turning in your hand as you try to brace them.
3" to 4" is a good reflex to start with and you end a flat profile to an inch or 2 of reflex when shot in.
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Okay. Thanks ;)
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I don't know of anyone here that adds as much reflex on a regular basis as mark St Louis, I would think some feed back from here would be valuable. I will very often start with 6" or 7" and as mentioned in above posts creates a lot of challenges. I think the biggest most obvious disadvantage is that if the wood and design are not up to the amount of reflex the wood will break down too much and you loose all the benefits from it. Another less often mentioned problem is that if you do maintain all the reflex your bow will often be unstable at brace without an exceptionally high brace height. They rock back and forth and want to flip themselves inside out. Everything has to be absolutely perfectly aligned.
About 3 years ago I was doing a lot of experimenting with addressing the problems associated with reflex. It all boiled down to reducing the amount of working limb to maintain stability and then adding enough width in the working area so you can make it thin enough to accommodate the excessive amount of bending it will go through. For the most part I have settled into gluing them up or heat treating in about 3 1/2: reflex and hoping to finish and slightly over 2" after tillering
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Good advise above!
It is a freaking challenge to go with a heavy reflex, but I like it.
But I got luckily some really good bows, esp. in combo with statics.
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Good advice given here.Done this many a time too mostly with sinewed bows.Only top quality type grained wood can handle this type profile and dead nuts alignment also.I've seen the option used to heat [dry or steam] the handle and fade sections into a deflex to help with this also.Still special attention needs to be given tillering these bows slowly.
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Agreed! Brace it up and let it sweat for 6 hours then decide the next step.
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So, Imagine a perfectly round bow, such that the cross section is perfectly circular at all points on the limb. Let's say this bow is also dead straight, and let's say it's made of something other than wood, like a tapered carbon tube. Just for giggles.
This bow can bend in any direction to take the string, right? Back, forth, to each side, basically, any direction you bend it, it goes. It's very hard to torque or twist when unstrung, and seems very stable. Except, once strung, the tips now are out of plane with the handle, and you could push one right and one left fairly easily. Not being co-planar provides them with a certain amount of leverage. Let's say now we want to reflex the bow. Baker says reflexing means that the tip moves more to take the string, aka bends the bow more (straightens from reflex to straight, then bends to the string), and thus provides a tighter string at brace height aka, higher draw weight early in the draw, which leads to higher total stored energy. So, good.
BUT, since the bow is equally stiff in in any direction, you basically COULD NOT POSSIBLY string a perfectly round bow against the direction of it's reflex. IT will simply roll, bend to the side, and take the string in the direction of it's reflex, not against it. Reflexing has again provided the tips with leverge that allows them to undo what you are trying to do. This is the instability that has been mentioned for bows with extreme reflex, and it persists to some degree even if we change the cross section.
OK, so let's take the same type of bow, make it bend to the same curve/tiller, but let's make it WIDER than it is thick, say twice as wide. Now, it can only bend easily back and forth, along its thinnest dimension, and it's much harder to bend it sideways toward it's greater dimension. BUT! This slat-like limb is much easier to twist when unstrung. It bends most easily back and forth, but once bent, pushing the tip from one side to the other is very easy. Also, near the tips, the ratio of thickness to width cannot practically be maintained or the bow will end entirely in the middle. Drat.
So, regardless of, and at the same time depending on, limb design, the more reflex you have, the more of these instability issues you will have. There may be a happy medium, but a limb with more thickness to width will have a rolling problem, and a wider, thinner limb will have a twisting problem. In addition....
Let's say we hit that happy medium, the limb is thinner than wide, but not twisting badly, and very reflexed. Now we have tillering issues. If the reflex comes out strongly from the handle, then we strain the wood mightily just getting back to brace, top and bottom limbs bulging forward then back. If every part of the limb bends the same amount, then later in the draw, the very rounded, bellied curve of the limbs gives very poor leverage from the string, almost like two very short bows attached to a set forward grip. So, the bow stacks. BY the time you tiller it out to 50 lbs what should be good early energy storage has disappeared and the F/D curve sucks. You've tillered what amounts to a good energy storing bow of lower poundage, that then spikes in draw weight at the end.
BUT! WE can avoid this allowing the limbs to bend aggressively near the handle! Right? Because a little bend here translate to a lot of tip movement! Yeah, so the outer limbs can be stiffer, maintaining good leverage out into the draw.......except.......that same principle means that the stiff limbs exert high leverage on those bending inner limbs, so your string tension at brace looks great, but there isn't enough working limb, so you have this long stiff lever, and not enough inner limb bearing the strain. So, you also end up with a LOT of set in the inner limb where it hurts you most. This bow now may look like a straight limb bow with a setback handle, and by the time you get the limbs around, you still have the same issues you did above, though less.
Finally, let's say most of the reflex is toward the tips. Here you may have plenty of working limb, but the abrupt recurves at the tips again provide "handle" that want to torque and invert the limb if allowed to. You rarely see an unstrung bow straight through the handle and straight through most of the limbs with large recurves, because the recurves act like big handles to twist the string off center and generally jack the limbs, AND, since the limbs are getting narrower toward the tips, their ability to bend off to the side is increased. Big recurves or big abrupt reflex requires more mass to keep stable, and that's a problem, too.
If I add big reflex or recurves to anything, it's deflexed first. Properly executed a reflexed stave can be a very fast bow, but thrade-offs add up.
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That's why making these type bows takes practice.Knowing what part of the limbs along its' length do most of the work and putting those parts of the limbs into the least amount of strain to do the most work in an overall tip set back profile with the lesser strained outer portions of the limbs.
Wood is wood.Some with different strengths and elasticity.Using top quality high in both catagories straight grained wood is your best chance of success with these highly strained profiles.Proper tip alignment and reasonable width negates all twisting.
I personally like tillering these type bows.A challenge with exceptional rewards if done properly.
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The biggest challenge with a bow reflexed to 5" or more is tillering to brace height. The bow is always trying to flip. Once properly braced then things can progress. I used to induce up to 10" of reflex while heat-treating, haven't made one of those in a long time. As was said, you need only the best of wood species that's clean and free of knots and it should be premium wood.
As to how much is too much, depends on the wood. Generally I would draw the line at around 10"
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Interesting discussion here!
I know what Marc mentioned above. I think leaving the limbs rectangular shaped (no rounded edges) or with a ridge in the middle on belly helps to hold the thing stable. Exercising a lot before bracing is a must. And of course wider limbs also.
Here is an example of mine, still my fav: http://www.primitivearcher.com/smf/index.php/topic,56785.0.html
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You have to remember that the tips move about 1/3 of the draw . So on a 28 inch draw the tips only move about 8".
Why does this matter?
If you consider a bow with no reflex is pretty much bending as much as it can stand... if you add say 3" of reflex it's the equavalent to trying to get 9" extra draw from the non reflexed bow!!! :o ... so don't be surprized if it takes some set.
Yeah of course this is a simplification, but I'm just trying to show you can't expect more than the wood can give, so don't get greedy.
Del
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I'm probably a bit overboard with this one. I gave it a thin coarse of sinew, waited, tillered and ended up with less weight than I wanted, so I reverse-braced it and added more sinew. Currently waiting for it to cure again.
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It is bending too much in the handle. Not trying to be a downer but I don't think you will gain much because the bow bends in the handle excessively.