Primitive Archer
Main Discussion Area => Bows => Topic started by: k-hat on September 08, 2012, 09:46:12 am
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Need your tiller opinions boys. This is elm, 60" ntn, parallel (1.75) for 1/2 length then tapers to 1/2" nocks. Got'r stretched out to 29" here, but only going to 28" (security blanket). Is it too circular for an eliptical tiller? Shadow makes it look like a hinge out of the left fade, just a trick of the light (my good camera's on the fritz, so no flash). Here it is:
(http://i1216.photobucket.com/albums/dd374/k-hat/raineyat29c.jpg)
Thanks for lookin :)
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btw, those are two offset elipses, one for each limb.
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There's two ways to look at this.
One is for proper bend to match your front profile. And yes it is too circular.
But,the other way is you are asking a straight 60" stiff handle piece of wood to be drawn to 29",so to get there you must ask the area out of the fades to bend more than it should technically.
So,basically your fine IMO
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I was bouncing around the same thoughts blackhawk. I went and looked at half-eye's 56" stiff handles and the tiller on those looks real similar (still can't believe he got 56" of wood to bend that well with a stiff handle!). I think i'll put some arrows through her and see how she feels. If I'm not happy with it, I'll loosen up the mid/outer thirds a touch.
Thanks again.
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k-hat,
Dont know that there is a "correct" tiller shape. But all of my bows I try real hard to get them circular and symetrical to each other (with or without stiff tips). It makes for a smooth draw and hard shootin bow.
Both the 54" and the 56" are going to Lesken 2011 from the site so maybe he can tell you his opinion on the performance impressions. He allready has the 54" and will get the 56" today.
I like the way your tiller looks, only difference is that mine would not have the tips you do. Mine would be thin rectangles with small pin knocks.
rich
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If your look at it this way it looks good to me ...
(http://i28.photobucket.com/albums/c210/coaster500/raineyat29c.jpg)
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I really like the way that is bending. I bet it will be a shooting machine. Dean
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Thanks half-eye, I really liked the way those two for Kenny turned out, unbelievable! I like pin nocks as well for my personal bows (though stringing a heavy bow with pin nocks can herniate a guy!), but this is going to someone else and i'm adding stringing grooves above the nocks to make it a little easier and keep him from torquing the limbs. A also used the overlays on this one to build up the slightly flipped tips to help with string angle/stack.
Thanks Dean, I hope she is. She oughta finish out at 50#, n the recip plans on sticking pigs with her :)
Thanks again guys for the input. I'll post when she's a fully finished bow or toothpicks ::)
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Right... Quick answer..
No!
Long answer (and I opologise to start with 'cos I'm going to be contentious here goes. :o. )
1. This 'The front profile determines the propper bend' is just nonsense!
Literally "non-sense" unless the bow is of uniform thickness e.g made from a dead flat board with no thickness taper.
And anyhow, even then, how do you correllate front profile to tiller shape?
If you cut a simple tapered limb say 2" wide tapered down to nothing at the tip from thin sheet material (e.g Triangular profile) it will give a curved tiller shape ... not a triangular one so where is this mythical correlation??
I just don't get it... maybe I'm thick... or maybe it's like the Emperors new clothes?
Thickness taper and unbraced shape are far more significant in determining the full draw tiller.
There I've said it now...I expect to be struck by lightning now! ::)
2. You have matched each limb to an elipse ... so how can it be too circular? It's not at all circular.
3. It's great! Stop worrying!
Del (scampers away to hide in secret cat nest)
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I'm just doin what i've been told Del, I'm only a year and 1/2 in to this! But I hear ya, no need to scamper away. i think i understand the rational, but i ain't got time to type my thoughts right now, it's date nite ;)
Maybe somebody who can elaborate will chime in while I'm out ;D
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I would think that it is as elliptical as you can get short of making it a bend in the handle bow, right? You would have to stiffen the fades to make the mid limbs work more in order to get a more circular tiller shape, wouldn't you? ???
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Looks good k-hat. As to your question of too circular??? This is one of the things I love about stick bows and those that build 'em. There is no law that says front view profile dictates tiller shape. However, front view profile in my opinion does tell us what the tiller shape should be to get the best performance. It's all about mass and movement of the limbs. If your limbs are tapered, a circular tiller works BEST because you are moving less massive mid limbs a greater distance and they are easier to move than heavy mid limbs. With parallel limbs and circular tiller, you are simply asking the bow to throw more mass forward than on tapered limbs. This comes at the expense of arrow speed. Additionally, tip deflection near the handle becomes a concern. The heavier the draw weight, the more circular the tiller because you have more stored energy to propel the limbs forward. The same is true for a longer draw length. All this having been said, it is not raw arrow speed alone that we are after. If it were, we would all be shooting wheelies with carbon darts. I turned off that road years ago. Still, we all aim for certain qualities with the bows we make, and efficiency in design has it's place. Do you like your bow? Does it release softly? Accurate? Those are the questions that REALLY matter. Nice work!
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I don't often give advice because I haven't the experience or knowledge to benefit. But if I had that bow I'd shoot it. I think you did a fine job with the tillering. Should you find that you are less than happy with the results I may be willing to trade you for some fresh cut staves.
I have elm, walnut, and mulberry.
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Thanks Slimbob, I'll have to think on that awhile but that makes sense. My explanation would have been from a more mechanical perspective (change in thickness w/parallel limbs vs change in width for pyramid), but I like yours better ;)
I guess what i was looking for was experience as far as the repercussions of having the tiller the way it is, so i could adjust if before i shoot it in. I plan to put those arras through tomorrow n see how she does.
Thanks for the offer Fred, but my boss has been waiting awhile for this one, so one way or another, she's going to him! Now, we might could work something out on another, i'm always in the market for staves!!
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I've taken the liberty of trying to fit an actual circle to it.
I found that a slightly flattened one (e.g an elipse) does fit best, the centre of a real circle would be at the point of the string where it is pulled.
You can see the centre line of the elipse is above that.
I still think the tiller is gorgeous :-* and not 'too' circular.
Del
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I have a question that relates to this issue and the discussion at hand:
What kinds of tillers are there, and what are the differences?
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I have a question that relates to this issue and the discussion at hand:
What kinds of tillers are there, and what are the differences?
Just my few pennyworth.
Basically:- Circular, whip ended, stiff ended and all shades in between.
There's what I call 'square' too which is one of the classic beginners mistakes... long stiff handle a hinge at mid limb and a stiff tip... one to avoid!
The above assumes a straight bow, if you then add in reflex and/or deflex it changes to look of the bow at full draw.
I hate the term 'Eliptical' as it is too vague and most tiller shapes are elipses of one sort or another (A circle is an elipse with major and minor axis the same length)
A 6' length of 2 x 1/2 will pull into a curve with most bend in the centre, but you could probably fit an elipse to it with the major axis running in the direction of the arrow.
I think people mean an elipse with the major axis running the other way,... it illustrates the possible confusion.
An arc of a circle is pretty unambiguous.
Del
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Del, i bet if i took that pic at 28 instead of 29" of draw the center of the new circle would be right on the nocking point ;)
Your clarification of ellipse vs circle is right on. It's also why my question was asking if my tiller was edging on being "too circular" of an ellipse. I guess we expect everyone to know when we say elliptical that we are implying the type of ellipse as you mentioned (long axis perpendicular to the arrow) as opposed to a "circular ellipse". I suppose it would be correct to say that your tiller oughta be some form of ellipse no matter what the profile!
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Steve Gardner's chapter on "The Mass Principal" in TBB IV (I believe), is the starting point for this topic. You asked for a more mechanical explanation as to cause and effect. Great place to begin. I'm not an engineer and my mathematically challenged little brain gets lost at a certain point on this topic. I can see that mass placement has an effect on performance, and that is what I keep an eye on. You asked what the possible effects of this tiller might be over a slightly more elliptical tiller (I agree with Del that the term is misleading)? Maybe no noticeable effect at all. If anything, a slight reduction in cast, more set near the handle and more limb vibration or hand shock. If when shot you see none of these things, then from a PRACTICAL stand point, your good.
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Excellent! You had to tiller the way you did to get that draw length from such a short stave. My only concern is that you may experience some stacking toward the late stages of draw. That happens when the string angle approaches 90 deg which is the case, k hat. Jawge
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Del, i bet if i took that pic at 28 instead of 29" of draw the center of the new circle would be right on the nocking point ;)
Your clarification of ellipse vs circle is right on. It's also why my question was asking if my tiller was edging on being "too circular" of an ellipse. I guess we expect everyone to know when we say elliptical that we are implying the type of ellipse as you mentioned (long axis perpendicular to the arrow) as opposed to a "circular ellipse". I suppose it would be correct to say that your tiller oughta be some form of ellipse no matter what the profile!
Now that's V interesting because my take on it is you'd need to draw it back about an inch MORE to get the perfect arc of a circle!
I think that really shows how confusing this lot is!
E.G. If the red elipse I drew was stretched down to become a circle, the centre would pretty much be your nocking point, however the bow would be flatter than the arc of a circle.
Heck! I'll just do it and post the pic!
Wow, according to the grid marks in 'paint' the blue is pretty much spot on circular and it sits pretty well on the bow.
I'd just love someone to post what they consider to be a 'better' eliptical tiller so I can see what shape it is. I think the pic shows how subtle some of this stuff is. You can almost fit any shape you want to the curve, that's the advantage of drawing a circle, you can at least measure and quantify the darned thing!
Del
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I hate the term 'Eliptical' as it is too vague and most tiller shapes are elipses of one sort or another (A circle is an elipse with major and minor axis the same length)
A 6' length of 2 x 1/2 will pull into a curve with most bend in the centre, but you could probably fit an elipse to it with the major axis running in the direction of the arrow.
I think people mean an elipse with the major axis running the other way,... it illustrates the possible confusion.
An arc of a circle is pretty unambiguous.
Del
...I am so confused... :o ;D
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I have to agree with Jawge. The length of draw that your going for on that length of bow dictates your tiller. For the best balance of performance and least amount of stack, you nailed the tiller. If you went for a flatter elipse, it would undoubtedly stack pretty bad. Great work! Josh
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Wow, it doesn't seem that long ago you stood in my shop and worked on taking that osage stave to a growth ring. I wish I could claim that I did something that helped take you to where you are today my friend...but I can't. We just didn't get that far. But you have progressed really really quickly on your own. Nicely done, your bow is lovely. The tiller looks fine to me, more than fine. :) I wouldn't change a thing. ;D
George
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my bad del, i was thinking backwards. you are correct. I was thinking that if i relaxed it to 28, it would make a different circle (which it would) but with a larger radius, not a smaller one (which was what i had in my imagination). As you said, that would put the nock even further from the center of the circle. Duh ::)
Slim/Del: My thoughts were along these lines (mechanically speaking from a stress/strain point of view): if you have parallel limbs that taper in thickness gradually, then the percentage of wood removed per inch to create the taper INCREASES as you move toward the tip (and as we know, changing the thickness a certain percentage has a much larger effect on resistance to bending than changing the width). This would seem to dictate that if you measured the amount of bend at each inch of the limb, it would INCREASE as you move from fade to the tips. This would create an elongated ellipse (ie not a circle). With a constant width taper from fades to tips and uniform thickness, the change in width being constant creates a constant/uniform change in resistance per inch of limb toward the tips. That would seem to dictate a constant angle of deflection per inch (as opposed to increasing as parallel limbs do) which creates a CIRCLE (ellipse with both foci at the same point... the center). i havent read Steve's chapter on the mass principle in a while, so i don't know how well this ties in.
I know this is oversimplified, I haven't even considered in this the leverage that each inch of limb exerts on the one before it (from fades to tips) also increases, which may completely negate all of what i said. Nor have I included what may happen if you have a width AND thickness taper at the same time >:D
All that put aside, if your limbs bend evenly without stiff spots or hinges, and fling an arrow, then you have a bow. Maybe even a good one. The rest i think is performance/comfort oriented (which i think is what you were discussing in your previous post, Slimbob), and maybe longevity as well.
Jawge: There is a tiny hint of stack the last inch or so, but it aint bad. At 28" the angle is still well under 90 degrees. I've put some arrows through, and at the right brace height she feels really good. Not jarring or anything. She she seems really fast too, well shooting across the garage anywho ;) Gonna take her for a spin in the back yard in a bit.
Appreciate ya'lls discussion on this. I think we often do confuse things by not being real consistent or even accurate with the terms we're using.
BTW Del: don't some of those short horse bows (mongolian and such w/siyahs) end up with a tiller that is an elongated ellipse with the major axis running along the arrow? :o
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Appreciate the kind words Doc! Think i kinda stumbled into it ::)
Thank you George. You've done more than you realize via our few conversations and interaction here on PA. I have a great deal of respect for you and your words carry big weight with me. if you told me the tiller was crap i'd probably just go scrap it and start again ;) I really owe thanks to a lot of guys here on PA and TG for helping me progress pretty quickly. It's like being apprentice to a couple dozen masters ;D So glad i stumbled on this little gold mine a year and 1/2 ago when i got started.
George i know i keep sayin it, but i do look forward to when we CAN get together again and make some shavings!! Maybe i can bring you one of my wacky hackberry staves and see what you do with it!
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I just put a couple dozen arras through her in the back yard up to about 18 yards. LOVE IT!! She is much more accurate than I am ::), and a pleasure to shoot. After several draws to 28", I actually didn't feel a hint of stack. She really sinks them in! At 6" brace, she is the quietest bow i've made so far. As my bowyer's knot loosened and the brace came down toward the end, i could tell she got a little noisier, so looks like 6-6.5" is gonna be ideal for her. I don't think the recipient is gonna have any trouble from the hawgs that get stuck by this little lady ;D
Of course I always fall in love with the ones that have to go away to someone else. Oh well, i can enjoy her for a little longer while i finish shooting her in and do the finish work.
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I think your above description nails the idea. When I started making these, there was little thought (at least by me) as to tiller shape, thickness, width taper, mass and movement, blah, blah, blah. We simply scraped until the tiller was good, and called it a calf-rope. I made a few whip tillered bows, under weight bows, heavy slow over built bows and a few that were, well, perfectly to my liking. Without regard to how someone else might feel about it. If you like it, and it appears as though you should, that's what counts. I'll bet the recipient loves it.
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Great discussion on tiller. I've made the mistake of tapering width and thickness to start a bow, but it seems to keep an even thickness and a gradual width taper makes the most sense.
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Matching tiller shape to the way the limb tapers in width is critical in my opion.
Parallel width then tapering quite suddenly into the nocks will require an elliptical tiller.
Pyramid bows a straight line taper from fade to nock will require a more arc of a circle tiller.
The parrallel width bow WILL have to have a thickness taper in order to bend like a bow. If the wood is tapering in thickness each part out to the nock is getting thinner and can/should bend further - elliptical tiller.
Pyramid bows on the other hand will have little to no thickness taper therefore if the wood is the same thickness it can bend the same amount - circular tiller.
Here's an experiment for anybody who doesn't feel that the above makes sense.
Make 2 bows.
1 that has a straight line width taper and 1 that has parrallel width out to 8 inch from the nock (then tapers into 1/2 inch nock).
Make the 1st bow with an elliptical tiller.
Make the second bow with an arc of a circle tiller.
Then repeat but reverse the tiller shapes.
Which 2 bows shoot the best?????
The really important thing with your bow is what does it look like unbraced? Where is the set? All bows will show where they are overstrained.
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Just to clarify my position in this excellent discussion.
It's self evident that you could get any shape tiller by tapering either thickness or depth and leaving the other parallell.
That's all I'm basically trying to say!
The best tillered bow will doubtless have a combination of the two and to try to put it all down to front profile seems an oversimplification.
I've heard the classic Holmgaard tiller shape being held up as an example of tiller reflecting front profile... but it doesn't! The levers are only stiff because they are thicker not because they are narrow and parallell! Without the thick tlevers it would be very whip tillered (or snap!)
Del
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Looks very good to me. :)
Pappy
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Thanks Pappy :)
I hear ya Del, i didn't understand you to be saying otherwise. I've only made two pyramid bows (and one bendy bow), both pyramids came out "rough" with about as even thickness as is possible (both boards). The tiller process resulted in both having a very slight thickness taper most of the length (guessing maybe 1/16-1/32").
Henry: I don't think tapering width and thickness is a mistake at all, unless you taper one of them too much! It seems to all go back to what do you want out of the stick.
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Del. Your right. You can get any tiller shape with any front view profile. The question I ask is, which tiller shape will give me the best possible performance with a particular front profile. I think what's getting overlooked here, is that initially this bow was 68" in length (I'm assuming it's the same bow). Early on when he was first tillering the bow, maybe had it drawn to 12 inches or so, he asked how the tiller was looking. I and a few others said that at 68" with parallel limbs, he should shoot for a more elliptical tiller. I believe that was good advice based on the bows parameters. At 68 inches and parallel limbs (assuming a 28" draw), when the bow is bending close to the handle, you are spending stored energy throwing a lot of wood forward. Add to that, a dense heavy wood. If the bend begins farther from the handle (elliptical), you are spending less energy because you are moving effectively, shorter limbs which are liter. The bows length and dense wood allows, or maybe suggests you do this. The bow ended up being 60 inches. That changes the equation a bit. You now have to get the wood close to the fades working to even out the strain, and you are working with shorter liter limbs to boot. I think a slight width taper from handle to mid limb on this bow MIGHT add a bump in performance for the reasons discussed, but we really start to split hairs. It's an academic debate. Interesting none the less.
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Your design dictates the shape of the tiller. Beyond that, when both limbs work evenly and the stresses are distributed evenly along the length of the limb (get out the tillering gizmo!) and you are at the draw length and weight you want, you're there!
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Same bow Slimbob, cept i was mistaken about the length. It started out at 64" ntn, then yes i piked it to 60" ntn. It went from 28" limbs to 26" limbs. Saw half-eye's creations and was a hair under the goal weight, so I said why not shorten her up and speed her up. She's elm and tempered and can handle it. Who wants to play it safe anyway? >:D I was actually thinking of trimming the width a little as you mentioned, mainly looking at mass characteristics, i've got a little weight to lose.
To me there's not much disagreement here. I sure appreciate y'all discussing this, I didn't realize I was gonna learn (and re-learn) that much from a "simple" question ::) I feel like i've definitely graduated to another level in understanding performance design characteristics. I can't imagine how long it would've taken me to get to this level of understanding on my own!!!
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How thick a particular piece of wood is will determine how far it can bend without taking set.
Thats the long and short of bow making.
When you have some taper in thickness you SHOULD have an elliptical tiller. If your tiller is circular then the inner limb is being over strained and this will be shown by that area having taken more set than it should have.
Sure you can make your limbs bend into whatever tiller shape you want but the wood will let you know when you've done it wrong!
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How thick a particular piece of wood is will determine how far it can bend without taking set.
Thats the long and short of bow making.
When you have some taper in thickness you SHOULD have an elliptical tiller. If your tiller is circular then the inner limb is being over strained and this will be shown by that area having taken more set than it should have.
Sure you can make your limbs bend into whatever tiller shape you want but the wood will let you know when you've done it wrong!
Ah Mike.
Indeed I can't argue with what you say, and to some extent I think we are arguing over how many angels can fit on the head of a pin.
The problem I have is that for every effect or rule of thumb there is an opposing word of wisdom. E.G people say in one breath 'You want eliptical tiller', but the next 'The Holmgaard design is one of the best', which does the opposite (putting all the bend in-board).
As I see it, it's about compromise, and I'm not saying eliptical tiller isn't the best.
I'm just saying it isn't necessarilly achieved by the front profile.
As a simplified example:-
You could tiller a bow to 90% draw with parallell limbs by tillering thickness only. You'd look at it and say, blimey it has all this excess weight at the ends and we all know the thickness contributes more to stiffness than width, also there is V little leverage at the tip. So I'll reduce the width of the tips until I just see the tiller/draw weight shifting.
Thus the front profile is determined by the tiller not t'other way round!
Hang on I've just realised I'm discuss ing gnat excrement and it doesn't really matter if A causes B or B causes A.
Del
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Well holmgaard style bows are well made then they should have a mildly elliptical tiller definately not having 'all the bend inboard'. The width on the holmgaard bow is widest at the fades and has a slow width taper which then 'steps in' out to the tip. This means that there will be a width taper which also means that the bend should increase out to where the 'shoulder' is. If you make it bend straight out of the handle then you are losing a lot of potential.
You say that having a parrallel width bow will give excess weight out at the ends...well not if it's bending correctly there. I've made bows that are parallel width until 8 inches from the nocks and they have shot 170fps plus which would indicate that there is no excess weight hanging about doing nothing! If it's bending close to it's limit then it isn't surplus to requirements.
I still stand by the thickness of the wood dictating how much bend it can take without inducing set.
Here are a few bows that correspond to the front view dictating tiller principle.
http://paleoplanet69529.yuku.com/topic/45302
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Mike! I shall have to give up trying to agree with you!
;D
Maybe it's just semantics.
I'd say front profile is 'reflected' in the tiller rather than 'determines' it.
'Determines' is just a bit too strong a word to me. Maybe I'm just a pedant.
Del
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Checked the PP link out Mike. Awesome bows. Love the BL bow. All three very sweet.
Del, welcome to the dark side!
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Mike i think what you missed in Del's example was "parallel limbs by tillering thickness only". If you considered your example in light of Del's, you're both getting the same end result, just from different methods. I take my daughter to camp every summer down in Austin. We have friends who take theirs as well. I go the major highways, he goes the backroads, but we both get there ;)
I kinda like the statement "front profile is affected by tiller" (or would that be effected?!?). Seems like a good idea to keep both perspectives in mind.
In fact, Del i think i'll try that on one of my next bows just to experiment. It would be interesting to take two "identical" staves and work one by tillering thickness, then narrow the tips, and do the other by cutting the front profile and initial thickness taper, then tiller the final thickness, and see how each turns out. Which one is more likely to end up on target?
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Mike i think what you missed in Del's example was "parallel limbs by tillering thickness only". If you considered your example in light of Del's, you're both getting the same end result, just from different methods. I take my daughter to camp every summer down in Austin. We have friends who take theirs as well. I go the major highways, he goes the backroads, but we both get there ;)
I kinda like the statement "front profile is affected by tiller" (or would that be effected?!?). Seems like a good idea to keep both perspectives in mind.
In fact, Del i think i'll try that on one of my next bows just to experiment. It would be interesting to take two "identical" staves and work one by tillering thickness, then narrow the tips, and do the other by cutting the front profile and initial thickness taper, then tiller the final thickness, and see how each turns out. Which one is more likely to end up on target?
>:D that sounds like the mother of invention ...i cant wait to see that build along!