Primitive Archer
Main Discussion Area => Bows => Topic started by: medicinewheel on January 19, 2008, 05:22:51 pm
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hi all! - what do you think of the tiller of thisone?? bow's pulled to 26" which is the final draw length, upper limb (on the right) has 1/4" positive tiller. not sure whether the lower/left limb bends enough!?
what do you all think?
thanks, frank
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i would personally take a few more scrapes off the left limb.
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If it has 1/4" positive tiller on top it should be fine. I would shoot it before I did anything drastic. Justin
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yes, the bow has 1/4" poitive tiller on upper limb and upper limb is an inch longer then lower!
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Yes, I would take a little more off of the left limb, but the tiller looks nice and even, good job!
Sean
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To me the right limb looks longer than the left, do they measure the same? Steve
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I would shoot it before I did anything else. I found if the difference in pos or neg tiller is too great the bow has a lot of handshock.
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Looks about right for asymetrical limbs.
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I'll never understand the that whole Torges shorter lower limb thing, they just never look right to me no matter how well they are tillered........
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Ryan, I am the same way, I do them on occassion but they never look right. I think it works at least just as well to keep both limbs the same length. Steve
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I'll never understand the that whole Torges shorter lower limb thing, they just never look right to me no matter how well they are tillered........
hey ryan and badger! - i'd believe a shorter lower limb is not better or worse then symetrical limbs; it's just a question of personal preference.
i have almost no experience with symetrical design, but i have a symetrical boo-backed cherry with ipé belly in the works. we'll see...
thanks all, frank
ps: wel, ryan: you complimented the tiller of my hickory-backed black walnut which was asymetrical. so i believe they can look right, too?! 8) 8) 8)
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I like the tiller, but would rather see it drawn by hand. 1" and 1/4" is a lot of tiller, at least for my personal bows. I get usually get by with 1" to 1 1/2" shorter and 1/8" or less but I tend to favor my lower fingers, kinda of 2 under with the index just hanging. Also I'd be mindful of how the bow sets from work. If it is concentrated in the inner limb, and you have weight to give, you might consider softening midlimb, which I see as very mildy flat on both sides. Again, it depends upon how you shoot it.
If you study the geometry of the drawn bow, you will find an inherent asymetry in EVERY bow. This due to the placement of the arrow above the pressure point of the bow hand, as we can't pass the arrow thru our flesh. However, it is not just related to the lever arm of the bow itself, but also by the bow string, and the angle each segiment (lower versus upper) makes with the corresponding limb. The result is this, positive tiller, in combination with nock point, had been developed and employed to offset this asymetry. It allows us to negate the tendancy toward rotation of the bow on the loose. Rocking lower forward is the tendancy we avoid, in order ensure force is applied to the arrow in a consistant, slightly upward way. When we fail to achieve this the bow tends to push the arrow into the rest on the loose.
Another method for combatting this inherent asymetry is to place the arrow pass closer to the dimensional center, negating the asymmetry of the upper segment versus lower segment string lenghts. Once you get used to the idea, every "even" bow you see will look like it is straining to make the distance at full draw on the upper, and slacking it's duty on the lower limb. These bows will tend to pull out of tiller on the upper, pull more positive tiller over time, if you aren't careful in awarding it enough extra wood to carry it's extra work, particularly during tillering.
That's just my opinion based upon study of the Tapley discussion of tiller and bow mechanics, and to some extent Kooi, linked therein, but mostly from just common sense. Again, would love to read citations which might contradict it.
http://goarchers.org.uk/mechanics/#
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Looks pretty good. I would just make sure the stave is starting to bend where you want it to. For me that is usually right at the end of the fades. I can't tell if your stave is doing that or how long your non bending handle is. Jawge
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I like the tiller, but would rather see it drawn by hand. 1" and 1/4" is a lot of tiller, at least for my personal bows. ...
DCM! - maybe i misunderstand terms: by 'positive tiller' i mean the distance between belly and string is bigger on limb then on lower limb, in this case here by a 1/4"
besides that, my lower limb measures one inch shorter then my upper limb. i never thought of that as 'positive tiller', but just as 'longer upper limb'.
what's right?
thanks, frank
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David will answer, but I think you might want a different set of conditions for an assymmetric limbed bow. The 1/4" positive tiller advice is generally for symmteric bows, I'd listen to David when it comes to tillering assymmetric bows as he's experienced and really good at it. By shortening the lower limb you are already making it a stronger spring, so there is less need to accentuate that difference with positive tiller. I think he's saying that an inch shorter does much the same as a 1/4" positive tiller, as far as making the lower limb stronger.
David, I agree theres no symmetry when it comes to a bow. So you pick your style and tiller it to be stable. I don't discount Torges' explanation of the benefits of assymmetrical limbs, but based on experience I think it can't be a huge advantage or the symmetrical design wouldn't be so widely employed, and successful.
I totally agree about doing final adjustments from hand shooting a bow. They look different from the tree (more or less depending on how your tree is set up) and even depending on who is shooting it.
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Frank if my understanding is sound, shortening the lower is the same in effect as making it stiffer. I am NOT saying shorteing it makes it stiffer, which while true is irrelevant. Rather that by making it shorter one balances it's inherent disparity with the upper, making positive tiller (used to offset this) less necessary. Seems to me we'd want our bows to shoot well with as little nock height and positive tiller as practical. These are by definition measures of asymetry after all. In the glass bow game it is largely irrelevant as there we don't have to worry about being so close to the edge of the elastic potential of the materials. Perhaps this accounts for our apparent fascination with what is labelled "even" but is in fact "shorter upper" limbed bows.
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lennie! - many thanx: i had problems to understand what DCM wrote in the first segment, now i get it. and i guess it's exactly what the problem here is! longer limb PLUS 1/4" makes to much bend.
i'll retiller the lower limb a bit, doesn't matter if i loose another 3 or 4 pounds; it's a lady's bow and it's still a bit to strong for her with 38#@26".
again, thanks a lot
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david! - thank you for your comment; i certainly understand better what's going on now!!! a lot of problems i had with tillering probably came from the same source: to much positive tiller.
i'll keep you posted on the corrections of the bow!
frank
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okay, took the tiller difference down a little; it's a bit more then 1/16" now and i'd say that helped it some.
what do you think??
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Frank,
We were having a rhetorical discussion about tiller, on the thread where you posted your bow. My first comments on this thread about your bow haven't changed. I would judge whether 1/16" or 1/4" tiller is "enough" based upon how it shoots, to some extent how it looks drawn by hand and how it takes set from work. For example, is it shocky, loud, take a lot of nock height for good flight, does it set equally along the entire lenght of both limbs? Again, I think it looks great, but thought was fine before you softened the lower limb as well, notwithstanding the aforementioned, which is the only way to really know.
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Frank, I believe David is right. The 1/4" positive tiller is to compensate for a bow having even limb length. I would still shoot it and decide from that, but 1/16" is probably better.
Perhaps this accounts for our apparent fascination with what is labelled "even" but is in fact "shorter upper" limbed bows.
The limbs are the same length on my bows. It is in the riser/handle that there is some question. ;) The bow certainly is not symmetrical though since the arrow passes above center and adjustments are made to compensate. Justin
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It is important to realize this whole discussion revolves around the 0" to 2" between the dimensional center and the arrow pass on our bows. In fact, I think relatively few people put their arrow pass at even 2" above (on a typical 2/4/2" "handle"), 1 1/2" being the more common. I guess my point in advocating this position, which seems to be my lot in the craft lately, is that placement of the arrow pass is a decision we make when crafting our bows just like every other one. How wide, how long, where the bend starts, what finish, etc, these are all decisions we make, one would hope with forethought and purpose. Just because some of us accept without question the decision to always go 1 1/2" above doesn't mean the choice doesn't have implications, and that someone else actually made the decision for us. I just don't understand why, if there is a benefit which is my belief, folks don't at least entertain the idea we have this option, while at the same time chasing nearly every other option with vigor and wonder.
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Frank
When it comes to full draw I go by feel rather than how it looks. If the bow feels good when you draw it and does not pivot in the hand then that is good, this of course as long as the limbs have no hinges and bend smoothly.
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Frank, it looks very well tillered, I just cant get my self used to the looks of a shorter lower limb. I've made a few bows that and I see no advantage to it. For me its more of a looks thing. I do the same as Marc, shoot the bow first before finding the sweet spot where the arrow should pass.
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Frank, check out the pictures when Sarah gets around to posting them of the bow I gave her on the christmas exchange. It has a shorter lower limb.
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How wide, how long, where the bend starts, what finish, etc, these are all decisions we make, one would hope with forethought and purpose.
Cant argue with that.
A 1/4" difference can be huge so I recomend shooting it before making any final decisions. Justin
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gentlemen! - i'm so sorry for the late reply; i have been through the busiest week in a long time!
david, i understand what you mean and i'm glad about the information contained! well the bow looked strange and felt a little unbalanced, too. but i couldn't really shoot the bow to find out, since it's to short drawlenght and to low poundage for me. the lady i made it for was pleased with it, but she is not experienced enough to tell me how balanced or not it felt when she shot it.
with the little adjustment i made in the tiller it now both looks and feels better to me!
i had similar problems before, so now i know what these problems originated from!
thanks to all for - again - helping me through a problem; i've said it before and i'll probably say it again in the future: this is the right place to ask when one has a problem in bowmaking!
well, the bow is one maple-backed purple heart and i managed to finish the bow with no frets or cryssals on the belly. today i found some time to finally sand it and do some build up of the handle! leather handlewrap and finish to come soon, than i'll post pictures of her in a new thread! she's going to be real pretty!
thanks,
frank