Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on November 04, 2015, 12:25:08 pm
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What is the advantage to an R/D bow other than looking really cool? It would seem that the R would cancel the D or vice versa. I tried a google search and all I got was peoples addresses(Rd)
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DC, an r/d bow has lower string angles and gives a higher force draw curve.
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I dont make strings yet. How do you determine the actual string lenth of a R/D bow? do you base it on the length of the bow before you put in the R and D? For instance if I have a bow that is 66 inches 64 ntn what lenght string would fit best?
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Stretch out a piece of string that will give you a zero brace height then subtract 3".
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Is there a rule of thumb for how much deflex to use? On the one I'm making now I'm sure I had too much as the string was hardly tight at brace. There was about 4" of deflex in a 60" bow. I took a bit of deflex out but the string still isn't that tight.
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It provides a sweet balance between smooth long draw with forgiving release and the performance of reflex. The deflex allows a longer draw and more forgiving release than a reflex only bow. The reflex provides the zip.
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In my opinion, best shooting bows made. Be it glass or wood. You know as soon as you shoot a well made RD why so many people want one.
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Is there a rule of thumb for how much deflex to use? On the one I'm making now I'm sure I had too much as the string was hardly tight at brace. There was about 4" of deflex in a 60" bow. I took a bit of deflex out but the string still isn't that tight.
I would suggest a simple rule of thumb is that you want the tips to be ahead of the handle some, maybe an inch or more, but at least in line with the handle. what some refer to as "Net Reflex".
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Thanks for the responses. I want to understand this a little better so more questions. If I have a nice straight 40# bow. 6" brace height and 26" draw length so it's about 2# an inch. Now I deflex the bow 4", string it back to 6" brace, will I have a 32# bow at 26" draw? Would it be 40#@30" draw?
If so, if I could magically increase the weight back to 40#@26, I could do so by adding thickness or width. If I used thickness would I be limiting the draw length? By width shouldn't change it other than draw weight. I'll stop there to see if anyone bites. I won't feel bad if no one does. ;) ;) ;)
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A deflexed bow is an entirely different bow than a reflex/deflex. Deflexed bows are very soft up front and stack. Not sure how much peak draw weight you would loose but you would loose a lot of stored energy.
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I was kind of working my way out the limb. I thought I would try to understand what the deflex does and then how the reflex sorts it all out. Maybe the wrong approach?
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The deflex in the handle saves the limb wood from having to use up too much of its bending capacity just to make brace height.
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That's a really understandable explanation, PatM. I was wondering the same thing.
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"If I have a nice straight 40# bow. 6" brace height and 26" draw length so it's about 2# an inch. Now I deflex the bow 4", string it back to 6" brace, will I have a 32# bow at 26" draw? Would it be 40#@30" draw?"
So, the final draw weight numbers may or may not be correct depending on the bow design and length, but for illustration, we can say they are close. However, draw weight has as much to do with leverage, as dictated by geometry, as it does with simple stiffness of the limb. But, let's look at what ELSE really happens.
First, by deflexing the bow, you are straining (by bending) the limbs less to get them to brace height. This means that the string is less TIGHT at brace height. This means that your draw WEIGHT for the first INCH of draw on the deflexed bow will be less than on the straight bow. The straight bow might pull 12 lbs at one inch, while the deflexed bow pulls 8 lbs at one inch. So, that also means that at two inches the straight bow may pull 14 lbs, but the deflexed bow might pull 10. This trend, of storing less energy at every increment at draw continues through the whole draw cycle. This is why we plot force/draw curves.
Now, remember that the MOVEMENT OF THE STRING added to the draw weight stores the energy. If you pulled on a giant iron bow with a hundred pounds of force, but the string didn't move and the limbs don't bend, you haven't stored any energy, and the arrow can't go anywhere.
Anyway, the deflexed bow will probably end up at a lower full draw weight, BUT, it is possible that because of limb geometry, both bows may end up at 40 lbs at 26", or darn close. HOWEVER, the deflexed bow will store less total energy, AND since it started lower, toward the end of the draw, it will stack, rising abruptly to the 40 Lb weight. This is why we work so hard to avoid set. However, the deflexed bow will be under much less strain at full draw, and therefore be less likely to take further set, fret, or break.
A R/D bow has VERY HIGH string tension for their draw weight. They store even more energy at every inch of draw than the straight bow. If the first inch is 8lbs for the deflexed bow and 12lbs for the straight bow, it might be 16 lbs for the R/D bow, even though they all end up at 40 lbs. In addition, toward the end of the draw, the R/D maintains a favorable, higher leverage string angle later in the draw cycle. So, not only are you storing more from having a tight string in the early draw, you also have better leverage and are storing even MORE by moving a stiffer limb more easily LATER in the draw. Recurve bows also do this, as do longer bows (compared to shorter) bows, and lever bows like the mollegabet styles, to some degree. But, energy storage is not a free lunch, and is not the only important factor in bow design.
A R/D has a couple more advantages. They are usually made as laminates, for one thing, and thus take advantage of the Perry reflexing principles. And because the inner limb (close to the handle) is already deflexed, it can be less strained (like the deflexed bow), massive (to protect it from failure), bend very little (while still translating to a lot of movement out at the tip), and still store a lot of energy total. So, good.
But, it's not a free lunch of course. High physical limb weight can cut into efficiency, and the curve of the limb makes it more prone to vibration than a straight- limbed bow. Incidentally, both of these are also inherently magnified in a recurve: the recurved outer limb often requires more mass to maintain stability, so there is often either a weight issue, or a vibration issue, or both. Also, they are tricky to tiller, sometimes, easy to hinge, and just generally take more trouble, time, and technique to make.
"If so, if I could magically increase the weight back to 40#@26, I could do so by adding thickness or width. If I used thickness would I be limiting the draw length? By width shouldn't change it other than draw weight. I'll stop there to see if anyone bites. I won't feel bad if no one does."
As I said, you may not need to "magically" increase the draw weight: it may simply be about the same, due to the geometry and leverage. More than likely, it would be a bit less, but since the deflex is present, the limb will be less strained, too. You could probably safely do either, given any given wood. You could offset the strain you lowered by deflexing by increasing the strain by thickness. The increased thickness would be more efficient, because it would take less weight to increase the stiffness. Hiowever, R/D bows and recurves basically MUST (in my experience) have flat limbs, either lenticular or rectangular in cross section. If you tried to R/D a bow with a round or square cross section, there is nothing to stop the bow from bending sideways as much as back to front, and will want to twist, turn, shed strings, etc.
Essentially the same thing is done on any R/D bow or deflexed recurve bow. If I want to make a bow with a big, high angle recurve, I generally deflex it and widen the limb close to the handle. The bigger the recurve (angle, diameter, and % of limb it occupies) the more deflex, at least in close to the handle.
A R/D bow is a LITTLE different, but principally the same. Appropriate amounts and ratios of R to D will depend on the length of the bow and the wood, the backing, and the limb width, just like the design of a straight self bow depends on these parameters. Basically, I go for a finished bow with tips ahead of the handle, but not WAY ahead. My forms deflex about 1-1/2" -2" from the front of the handle, and put the tips at LEAST that far ahead of the handle before tillering. So, back 2", and foreward 4". However, as you release a bow from the form, the amount of reflex and deflex will both settle into less than the form, so maybe 1.25" and tips only 1" ahead. So plan for that.
For maximum benefit from Perry reflexing, I generally glue up the core and backing, deflex the core with heat, or splice the core at an angle like Marc showed on that front page article a while ago. If I start with a 1.5" deflex and a 1.5-2" reflex (tips ahead of handle) I will end with tips about evenwith handle, or even, like 3/8" behind. Even with the tips a bit behind, you get the benefits of smooth draw and high string weight, but less and less so as they move in line with the deflexed portion.
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Thanks SB It's going to take me a bit to digest all this. Hope your fingers didn't cramp up typing all that ;)
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How is a R/D stave self bow made?
Is it better look for a deflexed stave and reflex the tips with heat or steam, or do you look for a reflexed stave, and deflex the handle?
Or do you start out with something straight, for preference, and add both?
Or any of the above, and it really doesn't make a difference?
Well.... I left out finding one naturally with all the curves already in place -- but that one I could probably figure out for myself... :laugh:
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It was explained to me as its the forgiveness of a longbiw with the zip of a recurve. That is probably way overly simplustic but thats how i understand it and its good enough for me xDp
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Dont know about Selfbows but R/D laminates seem to draw smoother and I think they take less set in the long run but I may be wrong about that.
I do know one thing for sure My takedown is smother than silk and has good cast, having said that I will make another for sure. Why would I want to shoot a bow that performs mediocre. ::)
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I like a reflexed stave to start and a little kink at the handle is easy enough within reason.i love elm because it bends like butter and is easily manipulated for that reason.
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Thanks SB It's going to take me a bit to digest all this. Hope your fingers didn't cramp up typing all that ;)
I did it between surgical cases over the course of 12 hours or so, so no big.
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It was explained to me as its the forgiveness of a longbiw with the zip of a recurve. That is probably way overly simplustic but thats how i understand it and its good enough for me xDp
Yeah, it kinda is. It's a darn good hybridization of the features.
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Plan B; with self bows you take what you can get. I prefer to reflex a deflexed stave over a form gently with heat. But, I often do find a stave that dries or grows with just too much reflex to handle normally, like 8" or something. So you can kink it back at the handle, or at the fades on each side, to get the total tip reflex to a manageable level. Either way. It helps to rough them down a bit first, of course, and it helps if the original deflex or reflex the stave had is even and symmetrical.
Bushboy is right, elm and some other white woods, and even osage and locust will tolerate a pretty big concentrated bend, even when thick, and really it only takes a few degrees. I have done all kinds of things just to learn about it. Like chopping and splicing at the handle, thinning and then building back up after bending, I even cut several saw kerfs to a consistent depth in the belly side of the handle, made the bend and then glued in shims.
I do think this works best in laminates, because Perry reflexing the right materials is like magic. But it's great with selfbows, too, and they shhot, esp since you have tempered the belly. I like that it is easier to bring the tips into alignment than it is with recurves, and that long gradual curves are much easier to convince the wood to settle into. I like that you can make a mildly R/D Molly and not have lateral tip issues much.
Technically, if you make a flatbow that takes a little set, heat treat the belly and flip the tips a bit, that is a R/D bow, but I think that engineering the deflex into the handle and getting that advantage is better.
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I'm getting ready to post a couple of DVD's in the Trading Post section. One of them is a new video that I got called, "Building the sinew backed bow" by Mike Yancey. In it he takes a straight stick of osage and turns it into an R/D bow with sinew. There are several aspects to his technique that I have never seen or heard of before and I plan to experiment with them myself. He puts a significant amount of bend into his staves and claims that, at least with osage, most of it stays forever.
If you are interested in the video look for my post in the trade section.......
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Ill add what I have learned from recent experience breaking two nice R/D bows during tillering. R/D bows need to be a lot thinner than other bows you may make. If your backing is more than an 1/8 of an inch thick or so you will have very little room for error when tillering. This happened to me twice. Once on a bamboo backed Osage bow and once on and Osage backed bamboo with Padauk accent strip. In both cases as I was trying to get it to weight it got to the point where my belly wood was thinner than my backing. Instead of just settling for an underweight bow I pushed it and broke both of them. From now on I will make sure than my backing is under 1/8 of an inch.
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Stretch out a piece of string that will give you a zero brace height then subtract 3".
So lay the string right on the belly wood to the nocks or just nock to nock without much tension?
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I like a reflexed stave to start and a little kink at the handle is easy enough within reason.i love elm because it bends like butter and is easily manipulated for that reason.
Thanks bushboy! That's what I would have guessed might be preferred, but I didn't know.
I do wonder if heat treating to create reflex is any different to the wood keeping its shape than creating deflex. When you heat treat to reflex something, are you compressing the back fibers to do it?
How does that work when it has to bend in the opposite direction when shooting -- like in a working recurved tip that was heat treated in? (I'm talking about just a simple wood stave bow, not backed or laminated.) How can it keep its shape?
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Has anyone here heat bend a straight bow and turn it into a deflex-reflex bow?
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yes,here's a elm made from straight stock.
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Front profile.
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Has anyone here heat bend a straight bow and turn it into a deflex-reflex bow?
Ive made and posted a bunch over the last few years...but they were floor tillered staves and not bows before i heat bent em. Its best to do it before you tiller it out all the way as itll wanna keep more of its induced shape