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Main Boards => The Bowyer's Bench => Topic started by: osprey1 on January 15, 2009, 08:49:00 PM
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Hi All: Was wondering if anyone has built a Dean Torges style of self or reflex/deflex type of hunting bow which has the lower limb usually an inch or two shorter than the upper. I have Deans book "Hunting the Osage Bow" where he goes into his reasons for building bows this way with the end result being a more balanced bow. Am thinking of building a R/D bow using this method. Have made a couple of hickory board bows with one being a Perry Reflex type. With both of these bows I laid the handle out right in the center. I think Eric has made this type of bow so am hoping he or anyone else might chirp in here with what they think of the different limb length approach. Thanks a bunch.
Tom :help:
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Tom, that is the best way to build a bow. The dymanic and static balance of the bow are closer together. I think they are much easier to make than an equal length limb bow. The equal length bow is easier to set out but are harder to tiller and have them stay in tiller...Glenn...
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sorry i dont understand, surely if a symmetrical bow shifts out of tiller, then so would an assymetrical bow? would a symmetrical bow not be eaier to tiller balanced, as the limds would theoretically have very similar bends/shapes.
would someone be able to explain the static and dynamic balances of a bow in laymans terms for a dummie like me!!
thanks
wayne
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I find a symmetric bow way easier to see tiller than an asymmetric bow. With the asymmetric design each limb bends differently. You have to judge the bend of each and compare it with the even bend of the other. I built bows for many years asymmetrical because that's how all the books at that time told you how to do it. A few years ago I began to build them symmetrical and my tillering improved quite a bit.
I don't think it really matters. Both styles of layout work well. My symmetrical bows balance well in my hand and come up smoothly when I begin my draw. It's a matter of what works best for you.
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Thanks guys. Like a lot of things it almost sounds like a personal thing. I haven't shot enough of either type of bow (asymetrical or symetrical) so I can't really appreciate the difference. Nor do I fully appreciate what a bow that "balances in the hand" truly means having only shot the two bows that I have made. They seem to feel pretty good. Its really great to hear the thoughts of guys (and gals)that have shot and built a number of bows and also from folks like myself who are still new to so much. Simply because I'm a newbie I don't want to deviate too much from a proven plan so I think I'll try to follow Dean's pattern as closely as I can. I know that on a bow that's symetrical one can flip to bow end for end to have the stronger limb on the bottom if it just happens to tiller out that way with one limb stronger than the other. With the other asymetrical design that wouldn't be an option.
Sounds like there are pros and cons to each design. :)
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I'm sure there are pros and cons to each way, but I don't think we've really touched the surface of how each way differs from the other. For me, the best way to start is to compare a string for a so called symmetrical bow, ie. arrow pass 2" above center on a 4" handle, to one where the arrow pass is closer to dimensional center. I think what you'll find is the the upper limb is shortened in the sym bow as indicated by the nock point on the string. Not so much so on the so called asym bow. Makes one wonder what the term sym is supposed to mean, when applied to such a design as the arrow pass 2" above center.
From my pov, the nock point is the point where the bow will apply forces, the central point of the bow. I can see no compelling reason to put it so much above center as to handicap the upper limb, and give the lower a free ride. Particularly in a bow where we want to work as close to the elastic capacity of the material as possible, like with an all wood bow. For a glass bow, theres so much extra work capacity I'm not sure it matters as much in that context. But I think even in a glass bow having the string segments, and consequently the corresponding bow/limb segments be as similar as possible (the triangles these elements strike) makes it a heck of a lot easier (for me) to assure they both draw and return in relative unison. When they are significantly different shapes (the triangle the arrow, limb, string make) it's harder (again based on my fevered way of thinking) to bring them into balance with spring force (tiller) alone.
Here's a site I cite frequently for some interesting background reading. Not for the faint of heart. In fact, I'd wager the average bowyer would be better served to simply do what they've been taught or have come to prefer with trial and error, or experience.
http://www.goarchers.org.uk/mechanics/
In particular the section in [Bow Mechanics] titled [Tiller] discusses the asymetry inherent in the bow/arrow/archer model, and the corresponding implications for bow design and tiller. To boil it down, both positive tiller and placing arrow pass closer to center have the same result, they mitigate the tendancy for the bow to rotate upper limb toward archer on the draw stroke, and the tendancy for the arrow nock to travel in an upward or downward curve on the return or power stroke stroke, versus traveling in a straight line.
This is an interesting topic. One where I haven't found a really, really compelling justification for one option over the other in practice, honestly. And one where a wide variety of opinions exist and imho, a fairly shallow understanding of the underlying geometry and physics, myself included. As such, sometimes folks can get a little testy during a long, detailed discussion. So while it interests me, I try to tread lightly in order to honor other folks preferences and pov. But I make most of my bows with the lower limb 1/2 to 2" "shorter" (which is a misnomer) than the upper.
I've never quite accepted the notion that the natural balance point of the bow, if suspended horizontally, has any relevance to how it shoots, "handles" or how convenient it is to carry in the woods. It's part of Dean's argument favoring the arrow pass at center, which places the balance point closer to dimensional center, the so called "draggin anchor" argument. I don't doubt it, it just doesn't come up as an issue for me when I'm totin' a bow around.
Everybody who knew I'd come along and write a book about this topic raise yer hands. LOL
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:wavey:
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When I set my bows up with the center of the bow being the center of the handle the arrow pass is actually only about 1" above the center.
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David wrote: "I can see no compelling reason to put it so much above center as to handicap the upper limb, and give the lower a free ride."
Remember in another thread where I mentioned that most folks forget about the bow hand David. Yes, the asymmertic string angle does add more strain to the upper limb using a symmetrical bow design. And less to the lower limb (the free ride you mentioned). Now if you throw in the bow hand and it's countering balancing effects you get equal strain on both limbs. That's why a symmetrial bow design can and does fuction very well.
Glad I could clear that up for you David. LOL!
ART B
:bigsmyl:
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Wow! I think there may an opportunity for some type of physics thesis on this topic. DCM really touched on a lot of very informative and interesting points. I had wondered about the natural balance point and the way the bow balances in the hand when carried horizontally. Very interesting. I tried this balancing with my bows that were laid out with the handle in the center of the bow and as far as I can tell they seem to balance pretty well. As Pat B mentioned this puts my arrow pass about an 1"+ above center. Then there is the other type of balance mentioned where the bow balances in the hand when the bow is drawn without rocking when drawn. I think one is trying to avoid having one limb tip more than the other towards the archer as the bow is being drawn. Can't say I have noticed this much either in my symetrical bows. Art B mentions the bow hand would seem almost intuitivly to counterbalance where needed as more drawing force is applied.
From what I am reading I am made to believe both types of balancing issues are so subtle that they might hardly be noticable in a bow where the arrow pass is situated in the true center of the bow (asymetetrical sytle) from a bow where the arrow pass is 1" or more above the true center of the bow. If so then then my inexperianced newbie brain has to wonder..... "if so then why bother with dealing with the extra tillering difficulties of a bow with a different limb length?" I guess I was really wondering what I was missing out on by building my bows with same length limbs as opposed to different length. Dean mentions the better balance and how the bow comes quickly to the hand etc. so it sounds like a very noticable thing but really I do wonder. May have to build a different lengh limb bow and see if I can notice the difference. Based on the range of opinions voiced here this is a highly debatable topic. :rolleyes:
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An extreme example of an asymmetrical bow would be the Japanese Yumi bow. These bows are very long(7'?)with the handle at about 1/3 the way up from the bottom tip. The arrow pass is well below the center of the bow and a Yumi archer is quite effective with this bow.
A bow is only as accurate as the arrow shot and the archer shooting.
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A symmetrical or asymmetrical design should soley be determined by how one grips their bow. Or at least that's how I do it. I wouldn't think that how one drags their bow through the woods could have any bearing on arrow pass placement or limb length differences.
Take a bow that's designed with the arrow pass 1" above center and shoot it with a low wrist/full grip. Here, greater stress is placed on the lower limb. Tiller profile will be hard to maintain if not completely pulled out of whack. Shocky also, because limb mass is no longer balanced.
Now take a bow designed with an arrow pass 2" above center. Shoot that bow with a straight/high wrist and see what happens. Greater strain is placed on the upper limb causing greater positive tiller and again, throwing off limb timing.
Me, I build both designs and grip 'em appropriately and they serve me well.
ART B
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hypothetically, why not build a bow with same length limbs, and pass the arrow at center of the bow, what would be the disadvantages of such design- besides the obvious longer riser, and subsequently longer bow?
surely way easier to tiller and maintain stability in the tiller. the nocking point would then be a negligable half inch(approx) above true center.
wayne
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Fujimo,
The inherent problem exists because you can't have the arrow pass at center if you are gripping the center.
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You can't grip you bow in the centre and shoot the arrow thorugh the centre. The centre of your hand is your centre of your middle finger and not the index finger so the shelf will be around 1.25 inches above centre which then makes the string length from where the arrow is nocked 2.5 inches shorter to the top limb than the bottom limb. This means you are placing a lot more pressure on your top limb through the draw. You can set your bow up to be shot anyway you like but the limbs must be tillered to hand placement on the bow and where the bows is drawn on the string...Glenn...
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Glenn, how are you doing these days? Hey, I've read where Tim Baker likes his rest set at 5/8" above center. Think I also read in one of Dean Torges' articles that he preferred 3/4" above center. These are very very low contact designs. From the pic's I've seen of Baker's shooting he's pretty much supporting the bow with the middle of his thumb. Makes for easier limb timing and a faster arrow from my experimentation with that design. Hard on the thumb though. But then again, these guys can do things that most of us can't!
ART B
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Art I always make my rest 5/8" (which is roughly half the measurement from the middle of the middle finger to the top of the index finger) above centre and I make the bottom 1 1/4" shorter, this places the arrow in the centre of the bow and I make the bottom limb stiffer, how much stiffer depends on hand placement and heel pressure on the bow...Glenn...
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ok, great now i finally understand that principle, never had it explained like that befor. so now how does one tiller the limbs to accommodate hand placement.
on past bows i have had horizontal lines on my tillering board- i have recognised that the two limbs will not match each other exactly in shape, but i would draw them at the approx. nocking point, and ensure that the tips cross the horizontal lines at the same time- always maintaining the desired shape in the limbs.
is this correct, or how can this be improved upon??
thanks
wayne
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Wayne my experience has been that if the bow is placed on the tiller board and drawn from the nocking point you will then see how the limbs will bend when being drawn. If the limbs are symetrical or asymetrical they will bend different anyway. You will know if you have done something wrong because one limb will develop more string follow than the other which says it needs to be strengthened. If you are using a lot of heel palm pressure to shoot your bow to me that says that the bottom limb is too strong and you are fighting it through the draw...Glenn...
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Glen, you say that "The equal length bow is easier to set out but are harder to tiller and have them stay in tiller".
Could you expand on this a bit for me. I would think a bow with limbs of equal length and the handle in the center would be easier to tiller but I have yet to build a bow with a shorter lower limb. I do know that when I made my first two symetrical bows I never felt right about putting the handle in the tillering boards cradle dead center and then pulling down dead center on the string. Then when the bow was finish tillered I would put the arrow rest on 1.25" above center and the nocking point opposite that and that was that. I had tillered to one set of parameters and then added another set of parameters (new arrow pass and nocking location) and began shooting the bow with these late and final changes away from my initial tillering efforts. This never felt right and I now am beginning to understand why.
With regard to the symetrical bow I see your points about the upper and lower triangles being different and the extra strain on the upper limb. I wished I had made a tracing of the equal length limbs on my first bows so I could see how much they changed tiller due to my inconsistant methods. Beginning to ramble here so back to my question. Is the shorter lower limb bow really easier to tiller than a bow of equal limb lengths?
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OK i have been howled down for this before and in Australia one person was so upset he wrote a derogerty 27 page critique about me on the internet. But anyway here goes. When you tiller and equal length bow the way you did and you placed your arrow shelf 1.25" above centre which is the way most of us do it the string length from where you nock the arrow is 2.5" shorter to the top limb than the bottom limb. Imagine how much extra pressure you are placing on that top limb when it is being drawn. It shows up in selfbows as extra string follow and uneven set and hand shock. Making an equal length bow with positive tiller and set up to be shot the way you have it will pull the bow out of tiller almost straight away. Strenghten that top limb or negative tiller the bow and it will take even set and will reduce handshock, it's amazing the difference it makes...Glenn...
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Thanks Glenn. Seems reasonable enough. The actual act of tillering the bow that is looking at the limbs and seeing if they are bending equally ....that would still seem to be easier on a symetrical type of bow?
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Tom, making a bow with a shorter lower limb is not new, it has been around for a long time, they were made that way because they ae better balnaced when being drawn. I have an old Andaman Is. selfbow here that has a shorter lower limb.
Best thing to do is make several bows and find what works best for you and the way you shoot a bow, but I would be looking at all options...Glenn...
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Glenn, we are fortunate to be members of this website that demands respect and tolerates nothing less. Everyone's opinion is welcomed..not always agreed upon but always respected.
Now if you guys will step aside, I'll tell you how it should be done! d;^) Pat
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No worries Pat, I know what you are saying. I use to have this idea in my head from what I had read that no bow should ever have a stronger top limb but it was on my second trip to the USA in 2000 I was shown by a bowyer over there that that is not necessarly true and he showed me why. I had been making selfbows since 1993 and they were mostly equal length limbed bows with the arrow shot above centre and positive tillered. While my bows shot well they didn't shoot anywhere near as well as the negative tillered bows I since then, but these days I much prefer a bow to have a shorter bottom limb. But as has been stated on here before if you change hand position and where the arrow is nocked that changes tiller when the bow is being drawn.
I don't know how other people get their shorter bottom limb but I mark the centre of the bow and go 5/8" below centre mark the handle 2" either side of that mark which is half of 1 1/4" which is how much shorter the bottom limb will be...Glenn...
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"Best thing to do is make several bows and find what works best for you and the way you shoot a bow, but I would be looking at all options...Glenn..."
Thanks Glen. For sure I will try to approach it that way. BTW I was doing a search and found a thread from last year called "symetrical vs asymetrical". I tried to copy the link over to post here but something buggered up. Under the search function (here under the Bowyers Bench) I typed "Torges" and it was one of the last threads listed. More informative great reading on this subject by many of the regulars here.
:-)
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I hate to have contributed, in some small measure, to Glenn's turmoil about negative tiller. While I appretiate his argument, it is sound within it's context, I do take exception to it as well. More specfically, the theory (in this context the word does not mean unproven, rather the opposite) is that negative tiller causes undesirable nock travel, that is nock travel in the nock down direction during the course of it's return along the power stroke. This could act to force the arrow into the rest, impeding performance and potentially causing tuning problems. Ideally you want the arrow to come off the bow as straight as possible, and the nock to travel in pretty much a straight line. In practice I think what happens is that other parameters of tuning, brace hieght, nock point in particular, and how the archer applies pressure with both his bow and string hands tends to cancel out the effects of, or actually mitigate the tendancy toward this nock down travel.
Negative tiller was first made widely public by Dean Torges in a article in The Bowyers Journal. While I agree in general with Dean's conclusions, including that cited by Glenn wrt to negative tiller, I think we (Dean and I) resolved that the nock travel aspect may be important, and was not much researched or covered by his article. They may have back issues at TBJ, and may offer subsequent issues where, for example, Gary Davis wrote another good piece on this topic of arrow pass placement, or relative limb lenght.
Most of all I think it's important for a bowyer who wants to broaden his understanding to a) become as aware and exposed to the underlying science (math and physics) as it practical b) keep an open mind c) try various designs and see how they work for you in practice. I you are like me, I'd built dozens of bows over the course of several years before I really paid much attention to the subject at all, preferring to just do what I'd always done, based probably on one example from a book I'd read while building my first bow.
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Gary Davis done an excellent job on explaining handle placement with his sliding handle diagram. Can't seem to remember him going into any details on adjusting ones grip to the different handle positions to help maintain tiller profile. Someone correct me if I'm misstaken on the latter (I borrowed that issue and don't have it for a reference).
Can't see any string nock travel when you keep equal strain on both limbs from the floor tillering step to finished draw length. Perhaps with unequal limb strain you might see this.
Can't see uneven limb set (as Glenn claims) when tillering while keeping equal limb strain either.
Pretty soon all this is going to dawn on folks that if you keep equal limb strain throughout the building process that you're not going to have the upper limb take additional set over the lower limb.
I'm in no way ragging on Glenn here. Hey, whatever he's doing seems to be working just fine for himself. If others can do the same then that's OK too. It's all about learning and having fun doing it.
ART B
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My perspective is that talking about bow making takes a really far back seat to actually making bows. but I still enjoy it so here goes.
I agree with you Art about having equal limb strenght to preserve working capacity in your wood bow. And that if your apparatus doesn't mimick pretty closely actual shooting by hand then the upper limb might well take more set from hand shooting. Heck, it is shorter after all, in most designs.
Glenn I'm sure will argue back that making the upper limb more stiff (neg tiller) forces some work load to the lower limb, as the upper won't bend as far if stiffer. With glass I'm not sure it matters, notwithstanding the effect of unequal limb strenght on nock travel, which while present doesn't seem to be very relevant in practice, at least in the cases Glenn cites.
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All I can tell you is that when you have an equal length limb bow and with the handle in the centre and you shoot the arrow 1 1/14" above centre you are placing more stress on the upper limb, a fair bit more infact.
It's has been admitted that the upper limb is shorter so therefore it must have more stress placed on it. What benefit would weaking the shorter limb have for the bow. None that I have ever seen, just makes the top limb take more set and doesn't feel real good to shoot.
If you make a bow with a shorter bottom limb you positive tiller it and if you an equal length limb bow and you make the top limb shorter by hand placement and arrow pass why wouldn't you strengthen the top limb which is now shorter.
It's the same with glass bows, limb length and hand placement and arrow pass have a big effect on how a bow shoots, infact it is very nocitable...Glenn...
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Glenn wrote: All I can tell you is that when you have an equal length limb bow and with the handle in the centre and you shoot the arrow 1 1/14" above centre you are placing more stress on the upper limb, a fair bit more infact.
There's some confusion, at least on my part Glenn, about that statement. How about clearing up something for me. I'm assuming we using the standard four inch handle for this dicussion. Most of us place our arrow pass at the top of our handles. Are you assuming the same?
Because with a same length limb bow with the handle dead center I would place the arrow pass 2" above dead center (that's one version of a symmetrical design). This leaves me with a 4" grip. This design requires a full grip for dymanic balance.
The way you described your 1 1/4" above center arrow pass, you would have 3/4" handle left "above" your arrow pass and that leaves you with a grip of 3 1/4". Is this correct? It's still a symetrical design but requires a straight wrist or lower contact hand grip to mantain dynamic balance.
Using proper grip with proper design you will not place greater stress on the upper limb. This bears repeating, the counter balancing effect of the "bow" hand is being ignored in this dicussion. And it can't be mimicked on a tillering tree. But trying to do so is what is adding the additional stress to the upper limb as you alluded Glenn. Just some humble thoughts on the subject.
ART B
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Pat I set my bows out with a 4" handle centre of the bow and the arrow pass is 1 1/4" above centre. I have never shot my bows with a straight wrist. I started making selfbows with this layout I always made them positive tillered and the top limb took more set but since I started to strengthen the top limb enough to have equal set on both limbs once the bow is shot in all I can tell you is that my bows are now a lot smoother to shoot, and this is true for my fibreglass-laaminated bows as well. Surely if a bow is talking more set on one limb is needs to be strengthened/..Glenn....
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Thanks for that clarification Glenn.
If one limb is being stressed more than the other Glenn then you're doing something to promote it during the tillering process. You use a tillering tree and pulling with a rope trying to mimick your draw?
ART B
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I don't use a tiller tree that much Art, only in the early stages and I will not use a tiller stick anymore that pulls the limbs down from the centre of the bow, I gave them away years ago. You can feel when one limb is pulling more than the other...Glenn...
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what I do is measure the center of the bow then place a mark say an inch above center.Then I cut an inch off of the bottom limb which brings the center of the bow to my second mark, which then becomes my arrow shelf
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That would make your arrow pass 1/2" above center I believe. How do you grip your bow? ART B
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no, it makes my arrow pass at center
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Close enough for me! :D ART B
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I think it puts arrow pass at center as well, but I don't understand how the process is any different by cutting the lower limb. I just find the center of the stave and place the arrow pass relative to that mark, generally 1" to 2" above.
I tend to use more high wrist than heeling. I think the more you heel the bow the lower you can place the arrow pass, and/or the more tiller you can use. But I always get the direction confused, of nock travel versus tiller, and arrow pass versus tiller. I think it is, the higher the arrow pass the more tiller and the more positive tiller the more downward the nock travel on return stroke.
I try to split the diff with the arrow pass placement so I can have a finished bow for my personal style of shooting with 1/8" or so of tiller and nock point no more than 1/8" or so above 90 degrees.
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No, that puts his arrow pass 1/2" above center David..........do the math.
That's incorrect about the closer the arrow pass to center the more you can heel the bow. It's the other way around.
You are however correct about needing more positive tiller when heeling the bow.
Since there is no nock travel at brace I believe any upward/downward nock travel at full draw is irrelevant.
Of course, all this is just my humble poinion on matters, take it for what it's worth.
:bigsmyl:
ART B
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"measure the center of the bow then place a mark say an inch above center.Then I cut an inch off of the bottom limb"
60" bow, mark arrow pass at 31" from the end of the lower limb. Now cut 1" off that lower limb end. The mark is now at 30" from the lower end, on a 59" bow. Correct? So, the distance from arrow pass to lower is 30", to upper is 29". The center of a 59" bow is 29 1/2". The arrow pass is at 30". Arrow pass 1/2" above center.
"that puts his arrow pass 1/2" above center"
Viola, you are correct Art! Thanks for keeping me straight.
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"That's incorrect about the closer the arrow pass to center the more you can heel the bow. It's the other way around."
"You are however correct about needing more positive tiller when heeling the bow."
This is the crux of my confusion, although I'm not yet convinced I'm wrong. I have long held, in my own debates w/ myself, that placing the arrow pass at dimensional center tends to mitigate the need for positive tiller. That they have the same effect, of reducing the asym inherent in drawing the string above where we put pressure on with the bow hand. By simply comparing two strings, one from a bow with arrow pass at center, another 1" to 2" above, one can see this exaggerated assymetry in the latter example (above center). By having unequal limb lenghts, we're forced to bring the bow back into balance by using the spring force of each, specifically by reducing the upper to let it bend farther because it is inherently shorter. I believe having the arrow pass closer to center helps put the nock point on the string closer to center, and thus reduces the need for positive tiller. But to be honest I have not resolved the issue completely for myself.
Seems like heeling a bow exaggerates this asym, and requires more positive to combat it. And if placing arrow pass closer to center combats it (as yet unproven in my thinking, but the idea I'm currently entertaining), then one might conclude having the arrow pass closer to center helps combat heeling in the same way as positive tiller. I base this on the spring strenght theory, as articulated by Tapley, and it's impact on nock travel, and the resulting incentive to positive tiller.
We may just be having a semantics disagreement, where we're saying the same thing in different words and perhaps don't realize it.
"Since there is no nock travel at brace I believe any upward/downward nock travel at full draw is irrelevant."
I would agree with you, were that my position. But it's not. Rather, my position is that the nock moves up or down as it moves along the path from full draw to brace during a shot. This I think is irrefutable. One can find lots of demonstrations all over the net, Paleoplanet for example had a thead recently. I was first exposed to it perhaps 8 years ago by Steve Harville. He may have is blog up still. But whether it is relevant is certainly subject to debate.
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I think that asymmetrical string on a symmetrical bow is what is throwing you off David. It's hard to comprehend that a short string angle and a long string angle can produce even bending limbs with the symmetrical design. Well it can't by its self, that's where the counterbalancing bow hand comes in.
As you know, a long tillering string unneccessarily works the inner limbs (comparing this to the upper string angle of a sym design). Now the bow hand does exactly the same thing. This is why I think you get a perfect sym designed bow to bend evenly even though it's accomplished with a asym string. Just my opinion here folks. Would love to hear others.
I agree with you on having the arrow pass as close to center as possible. But only if both limbs are made the same length. ART B