Primitive Archer
Main Discussion Area => Bows => Topic started by: arachnid on January 28, 2014, 06:31:20 pm
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Hi Guys.
I was researching the other day about tillering a pyramid bow and the concept "circular tiller" kept popping up
(Tim Backer mentions it in TBB Vol.2, concerning board pyramid bows and other guys here and in other forums).
I was wondering if someone can give my some clues to the difference between circular and eliptial tiller.
Pics would be great (if its no much to ask...)
Thanks.
Dor.
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Circular tiller... bend thru the handle, yew selfbow ELB. Tiller prescribes an almost perfect circle... bending 'full compass'
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Victorian style ELB target bow, with just a sniff of a stiff handle and tips. Tiller becoming just slightly elliptical.
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Pyramid flatbow. Non-bending handle. As round as possible, but without bending thru the handle, tiller becomes slightly elliptical.
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I don't have a pic of really elliptical obvious elliptical tiller, but the handle and tips would be reasonably stiff, prescribing more of an elliptical tiller shape at full draw. All these tiller shapes are correct, and are properly applied to the appropriate design.
I'll search and see if I can find one....
If anyone has a nice elliptical tiller... please post it.
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Here's a hickory selfbow. A flat bow, with parallel limbs for the first 10" ... about as elliptical as I get.
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Hmm, I'm still kinda confused.... I think I need to see about ten more of your english longbows Adam, to fully understand the difference between full compass and elliptical. And of course this has nothing to do with wanting to drool over more of your sweet elbs... not in the least..... >:D
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Not primitive but I like messing with pictures on the computer...same order...as posted above. You do have to be careful - you can make the shape fit the bow in different ways. It is just a tool - but sometimes makes it easier to "see". Look at the shape of the shape I added - more circular or elliptical.
Nice bows BTW!
Mitch
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Shape regardless, that really shows just how damn good Adam's tillering is! Holy cow.
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Yep that is for sure!
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Shape regardless, that really shows just how damn good Adam's tillering is! Holy cow.
Thanks, Will. Not tryin' ta show off, just tryin' to answer the fellers question with pics, like he asked. It took me years to 'see' tiller properly, and to be able to see the subtle differences.
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The simple reason behind using one or the other is that as wood gets thinner it can bend further without taking set.
A flatbow with parallel width limbs for most of it's length has to have some taper somewhere. So the taper is in the thickness.
So the thick bit near the handle can't bend much but as you move along the limb towards the tips the limb is getting thinnerall the time....therefore it can (and should) be bending further as it thins. eg. elliptical tiller. The bit you can adjust with this design is how much of the limbs are the same width. If there is only say 4 inches with the same width out of the fades then that bow should have that first bit of the limb moving less than the straight taper out to the tips (this bit should be circular - no thickness taper). As you extend that parallel section out further then the tiller should become progressively more elliptical.
A pyramid tapered bow however has the majority of it's taper happening with the width. This means that there is very little thickness taper (usually!). So if the limb is staying a constant thickness for it's length then of course each bit of the limb should be bending the same amount eg. circular tiller
Messing about with and understanding this principle is the key to making good bows in my eyes.
Adb - have you noticed that you get less set,handshock and better performance with an elliptical tiller on your longbows. I certainly have. Only once the weight is up over about 80# do I start deviating from this tiller and start to get the handle working more. If you think about it elb's have a large amount of thickness taper going on.
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Thanks a lot guys!
especially Adam for the great pics (damn it man, I wish I could tiller a bow that good. I have A LOT to learn...)
and Mike for the very good explanation. I think I got the idea. I`ll try it out.
Thanks again guy.
Great people in a great forum!
Dor
Israel
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The simple reason behind using one or the other is that as wood gets thinner it can bend further without taking set.
A flatbow with parallel width limbs for most of it's length has to have some taper somewhere. So the taper is in the thickness.
So the thick bit near the handle can't bend much but as you move along the limb towards the tips the limb is getting thinnerall the time....therefore it can (and should) be bending further as it thins. eg. elliptical tiller. The bit you can adjust with this design is how much of the limbs are the same width. If there is only say 4 inches with the same width out of the fades then that bow should have that first bit of the limb moving less than the straight taper out to the tips (this bit should be circular - no thickness taper). As you extend that parallel section out further then the tiller should become progressively more elliptical.
A pyramid tapered bow however has the majority of it's taper happening with the width. This means that there is very little thickness taper (usually!). So if the limb is staying a constant thickness for it's length then of course each bit of the limb should be bending the same amount eg. circular tiller
Messing about with and understanding this principle is the key to making good bows in my eyes.
Adb - have you noticed that you get less set,handshock and better performance with an elliptical tiller on your longbows. I certainly have. Only once the weight is up over about 80# do I start deviating from this tiller and start to get the handle working more. If you think about it elb's have a large amount of thickness taper going on.
Well said.
mike... no, I don't notice an appreciable difference with a more elliptical tiller, as far as set goes. If I do my job well, any bow I tiller will have minimal set, regardless of design. I do notice better performance with stiffer tips, however. Performance to me being a combination of arrow speed and shootability (ie minimal handshock, etc.).
I think ELBs have basically nothing but thickness taper. That being said, I tiller my warbows with a more elliptical design than I used to. They perform better, but I have to be careful they don't take more set, being that the grip and tips are a bit stiff. If I can pull this off with a heavy draw weight warbow, it has amazing cast.
Something I learned long ago: even tapers (either width or thickness) make even bends. If you can keep your tapers smooth and regular and even, the wood will bend evenly for the most part, and final tiller will only require small bits of tweaking.
Just remember... for best results (low set, good performance) the tiller shape should match the design.
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Thanks a lot guys!
especially Adam for the great pics (damn it man, I wish I could tiller a bow that good. I have A LOT to learn...)
and Mike for the very good explanation. I think I got the idea. I`ll try it out.
Thanks again guy.
Great people in a great forum!
Dor
Israel
Welcome!
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By elementary school most of us are taught and know the difference between a circle and an ellipse, and its as simple as that.....a whole lot of explaining here making it more difficult than it really is...
^--- thank you captain obvious :laugh:
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Some of the new folks need visual aids. Pictures speak a thousand words. 'Seeing' tiller is not easy early on in bow making.
I almost went this route of the obvious difference between a circle and an ellipse, but for some people (obviously) it's not that simple. Or knowing how to apply what where.
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Captain Obvious must have slept through his elementary school manners class, eh?
adb: agree with you that the photos are most helpful to those trying learn something.
rich
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Those bows are all very beautifully tillered bows. I'd say Mitch's first pic shows a circular tiller while the others look pretty elliptical to me.
Jawge
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I like to think of it as tiller logic, using a good logical reason for tillering the bow the way we tiller it.
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I really think a bow can be circular in the sense that the whole bow describes an arc of a circle or the working limbs describe two separate arcs of a separated circle.
That may make the general arc of the whole bow appear to be an ellipse, but it seems that this is still just two arcs and three flat spots creating that illusion.
There are other more accurate terms to describe an arc with a progressively increasing bend.
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Something I do when making forms for heat treating in reflex is to take a string with a pencil on one end and wrap it around something. As I unwrap it the radius of the circle grows larger giving a nice smooth elipse.
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That's what I mean Steve. That is not technically an ellipse. It is is called an involute curve.
http://en.wikipedia.org/wiki/Involute
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Cool Pat, I think involute better describes a desirable curve. Now we have a new word we can use! Primitive bow builders are the greatest bunch of information sharers on the planet. I bet within a year involute will be shoing up on forums.
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Mikes explanation on the first page makes the most sense to me, now I have a good understanding of WHY. I kind of had an idea, but now I know exactly. The problem I found was, you'd be reading about a bow and someone would say it has circular tiller... oh but the handle is a little stiffer and the tips are slightly recurved... then I start getting confused again :P which of course comes down to lack of experience. This is a great thread for the new people though, like me.
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Man! Im glad I have no clue how or why I tiller like I do, this thread hurt my pea brain.
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I think truly circular tiller is not common. Other than bend thru the handle ELBs (which are not common), warbows, or short paddle bows, etc., a perfectly round tiller is much less common than a typically elliptical (or involute curve ::)) tiller. Even the pyramid bows (which I build tons of) end up with more of an elliptical than round final tiller shape, especially with a non-bending riser. We've all learned to avoid whip tillering, and leaving the tips just a bit stiff, to improve performance. Conventional wisdom says to tiller a true pyramid bow (with continuous width profile taper), as round as possible. I just don't think it's possible to make such a bow with a perfectly round tiller.
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Pearl, even if you don't it is kinda fun to think we do!
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I don't know... when I set out to build a bow, I certainly have a goal in mind. Besides draw weight, draw length, and design, I'm visualising the final tiller shape before I begin. This helps me minimise set. Admittedly, I don't always get there. Sometimes this breeds innovation, but mostly you end up with something less than you want.
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ADB, I know exactly what you are talking about. I have never had the greatest eye in the world so I try to find ways to identify shapes earlier. Biggest problem area I struggle with is the transition are about 10" to 14" inside reflexed tips where it quickly becomes static.
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This is real interesting, thanks for the pictures, Adam.
arachnid; I sent you a PM.
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Whip tiller IS probably the best example of elliptical tiller that there is...
People in the bow world hate to modify terms to make them more accurate once they are set in defining something a certain way, even if incorrect.
Hence the Mollie/Holmegaard confusion to this day.
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I think there is a big difference between whip tillered (which in my mind is an incorrect tiller) and elliptical tiller. Whip tillered infers the bow is bending no where but at the tips, which makes for a less than ideal bow... one which will take excess set. To me, a whip tillered bow is just a short bow with a very long handle.
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Really? I would just say it bends excessively, not "only" at the tips. It would be virtually impossible to make a bow that only bends at the tips and has any sort of normal profile to the inner limb.
Take an image of an ellipse and put a string across half of it. Bingo, whip tiller.
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I think you're missing the point, but carry on.
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I'm a total beginner so bear with me, but isn't "whip tillered" just short for "whip-ended tiller"?
As in, the bow is tillered just fine, but the very tips (say the last 6" or so) suddenly both bend more than the rest of the bow, almost like two equal, smooth hinges?
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Which is exactly like half of an ellipse....
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In a nutshell the thickness of the limb dictates how far it can bend. As the thickness changes so should the amount of bend.
I think it''s essential to understand this (or if not understand at least adhere to!) if you are after any kind of performance.
As Badger says - tiller logic.
Getting hung up on the minutiae of descriptions doesn't really help! The problem is we have a whole variety of different bends to describe with a couple of words so of course some of the descriptions aren't wholly technically accurate....
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I may start out with a tiller profile, draw weight etc. in mind - but nearly every time I do the wood tells a different story. A knot here a kink there and before I know it the wood is telling me what to do not the other way round.
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This is all well and good, but there are a couple of problems with the concept.
1. Eliptical is so vague as to be virtually meaningless! >:D After all a circle is an elipse that just happens to have its two focii at the same point!
A straight stick when strung and drawn will look eliptical (with stiff tips)... but the long axis of the elipse will be in the direction of the string rather than along that of the bow!
2. Any bow with a stiff non bending grip section will tend to look eliptical. E.G If you take an arc of circle tillered ELB and stick 8" of stiff riser in the centre, it will fit an elipse better than a circle.
3. How much of the ellipse do you take? If you take a complete half an elipse, that would be whip tillered! You may notice, I usually say 'arc of a circle' tillered rather than 'circular' as the bow doesn't form a circle nor even a semi circle. It can get fairly close to a semi circle, but would probably be stacking badly by then.
4. I think if you try too hard for 'eliptical' it's easy to over do it and end up with the outers working too hard, or whip tillered. I actually go for a very fat elipse or slightly flattened circle when drawing curves onto pics of my bows.
I think it's a useful term to describe what Mike has explained, but it shouldn't be taken too literally.
After all, eliptical with stiff tips and a stiff centre section isn't a section on an ellispe any more!
Del