Primitive Archer
Main Discussion Area => Bows => Topic started by: Knoll on December 05, 2014, 02:14:26 pm
-
I've made a few bows from boards. All relatively narrow (ala 1 3/4 or less) with various width tapers ... beginning at fades, 4" from fades, and some as much as 12" from tips. And usually constant thickness. I've tillered all of them by reducing wood from belly. Never from edges.
Now I'm about to begin tillering my widest-limbed bow ... 2 1/4". Width is constant to 4 1/2" beyond fades. Then tapering to 1/2" tips. Thickness is constant too.
I've come to understand that pyramid-tapered limbs should be tillered by removing wood from edges, not from belly. While my past approach of removing wood from belly has resulted in shootable bows ... how truly good they are I don't have enough experience or chrony to judge.
Since this bow is so wide, I'm thinking maybe I should tiller this one by removing wood from edges.
What are the advantages of doing so?
Use a rasp in beginning stage, then scrap, & then sand? Constantly re-rounding edges?
This bow will be a new adventure .......
-
I'm not sure where you got the Info on side tillering pyramid bows, I've built a ton of them and don't think I've ever side tillered one, I start with an even thickness but buy the time I'm done tillering there's usually a silght thickness taper
-
Tillering from the edges is possible with a wide limb...say around 3 ". Never done it though.
I've tillered log staves from the edges when they don't respond to belly wood removal.
I've tillered narrow (2 in) pyramid shaped limbs from the belly.
There's no hard and fast rule. IMHO.
Jawge
-
It really depends if you subscribe to the front shape matching tiller shape mantra.
I don't. Wood is not that smart.
-
if you have the bow tillered well and want to reduce the weight,, from the side is good,,
-
if you have the bow tillered well and want to reduce the weight,, from the side is good,,
Exactly. It's easier to scrape 1/2" evenly than 2 inches.
-
A read of the subject of "pyramid" bows in Archery the Technical Side would dispel all these misgivings.
The whole purpose of a "pyramid" design is to have the whole limb at the optimum thickness for the amount of bend desired.
Then, the whole length of the limb, the width is appropriate for the weight desired. A straight taper accomplishes this--with one necessary modification. Ideally, the taper would form an apex at the tip of the limb. But the tip needs to be big enough to hold the string. So, the limb should be tapered only to where the sides are about a half inch apart. From there, the last few inches of the limb should be parallel to the tip.
With that design, the limb will be perfectly or almost perfectly tillered right off the saw. If not, narrow the limbs where needed.
-
A read of the subject of "pyramid" bows in Archery the Technical Side would dispel all these misgivings.
Thanks for pulling the quote.
So, an optimum pyramid design is one where width taper and thickness is so close to ideal (given weight/pull objective) that little tillering is needed. Much the same could be said for any design ... that limbs are sized so close to optimum that little tillering is needed.
For a 50#/28" pull bow I guessed at 2 1/4" tapering to 1/2" and thickness of 15/32". Not surprisingly, those dimensions yield limbs too stiff for the objective. So, according to Jim Davis, limb width is where wood should be removed. Correct?
-
What kind of wood we talking about ... osage, mulberry, hickory or ash....it all makes a difference to limb thickness, related to width.
DBar
-
Yes it does matter what kind of wood. But there is one thickness for each wood in a "pyramid" design that is right for each length of limb/draw length combination. There is no number that can be attached to any of these situations, but there is aright thickness.
A read of the subject of "pyramid" bows in Archery the Technical Side would dispel all these misgivings.
Thanks for pulling the quote.
So, an optimum pyramid design is one where width taper and thickness is so close to ideal (given weight/pull objective) that little tillering is needed. Much the same could be said for any design ... that limbs are sized so close to optimum that little tillering is needed.
For a 50#/28" pull bow I guessed at 2 1/4" tapering to 1/2" and thickness of 15/32". Not surprisingly, those dimensions yield limbs too stiff for the objective. So, according to Jim Davis, limb width is where wood should be removed. Correct?
Thickness that is right for the amount of bend takes into account the length of the limb. As for your example, no, if your bow is around 66" ntn, the limbs are plenty thin enough to bend without taking set. The bow has more width than you need if it is too stiff. It should be narrowed in straight lines--the fades should be narrower but the nocks should be left as is.
Lots of us have found these things to work in practice (for at least the last 75 years) and the math of physics bears it out.
I did not discover any of these ideas or practices. I just do them. There is no reason for me to defend them, I had only hoped to explain them. A foolish goal, perhaps.
-
Yes it does matter what kind of wood. But there is one thickness for each wood in a "pyramid" design that is right for each length of limb/draw length combination. There is no number that can be attached to any of these situations, but there is aright thickness.
Agree 100% Jim ;) But everyone was talking a lot of dimensions... :-\
DBar
-
So, Jim, if wood is removed from edges, roughly how much would recommend to remove before putting the bow back on tillering tree to see where you're at with weight/pull/bend... particularly during early tillering when ya know good bit needs to be removed, but don't want to "over do it"?
-
So, Jim, if wood is removed from edges, roughly how much would recommend to remove before putting the bow back on tillering tree to see where you're at with weight/pull/bend... particularly during early tillering when ya know good bit needs to be removed, but don't want to "over do it"?
If your limbs are of even thickness from fade to tip and the sides are a straight taper, you can figure out exactly how much narrower to make the limbs to reduce the draw weight to what you want.
If the bow pulls 50# and you want 40#, the width needs to be 4/5ths of what it is now. If it's 2-1/2" wide at the fades, it needs to be 2" wide to pull 40#. Leave the tip width or the width where the tip becomes parallel unchanged.
The bend will stay the same curvature no matter how wide or narrow the taper, barring any change in relative stiffness by the loss of local relatively stiffer or weaker wood. That is, if the wood is of uniform stiffness from fade to tip, the curvature will not change by narrowing the triangle.
-
Asharrow has nailed it on the head!
-
It really depends if you subscribe to the front shape matching tiller shape mantra.
I don't. Wood is not that smart.
EH?
It's not about wood being smart it's basic physics. Wood certainly isn't smart enough to think itself above and beyond the laws of physics! Thicker material won't bend as far as thinner material - simple. A constant thickness limb should be bending the same amount along it's length.
-
The statement "The curvature will not change by narrowing the triangle" (by Asharrow) caught my eye.
I'm not sure I agree...
I'd already been considering this subject, indeed I've been pondering it for about 50 years.
There must surely be an optimum taper for a bow of even thickness to give the arc of circle curve. ( ? )
IMO this is self evident because if you take the taper to one extreme* e.g zero taper (parallel) we all know most of the bend is near the grip.
OR... maybe the whole thing is self compensating and the theoretical taper is always to zero tip width and the actual angle doesn't matter ...
It's one of those things I mean to try sometime as I have a load of polycarbonate sheet which could be cut out into nice trial shapes.
Del
Of course the real extreme is tapering the wrong way with tip wider than grip >:D
-
I highly recommend Paul Klopsteg's review of this subject in Archery the Technical Side. Clarence Hickman looks at it too in the same book. Also, a look at the mechanical data for flat springs in Machinery's Handbook is revealing--and encouraging.
Jim Davis
-
Good observation, Del. In a pyramid bow the tiller should be rounded. That means the wider, near handle wood needs to do its share of the bending. Otherwise, set will be impacted.
Jawge
-
Right let's design an experiment!
My polycarbonate sheet is 3mm thick.
I can cut out several bows 40" ntn . If they are all 40" ntn with no grip at all, (e,g straight line symmetrical taper from the centre line to the tip) that's one less variable to consider.
What do we think is the best taper?
What is the best starting width for a 20" limb?
I'd suggest maybe going extreme as we can cut 'em down after.
Say 3" wide tapering to 3" (e.g.Parallel, although this may break... mind polycarbonate is pretty tough)
Then 3" tapering to 2"
3" tapering to 1"
3" tapering to 1/8"
I can use the same string on each and a low brace, say 1" and draw to 16" ?
Now obviously I don't want to do a load of work and have folk say I should have done it different... so if we reach some sort of concensus I'll do the test and take the pics. I can keep a fixed camera set up.... heck I can even take video, edit it togethjer , put music to it and release it in time for Christmas. :laugh:
What do the gang think?
Del
(IMO. A well designed experiment trumps pages and pages of theory)
-
I think that in order for it to be an arc the taper has to go to zero. So I think you need to cut a poly limb say 4" tapering to zero, bend it, take a picture, slice it in half(2" to zero), bend it , take a picture and then do it again. That will give you three pictures to compare. I'm not sure what the 3" tapering to 1" will do. It might be an arc too ??? ??? ???
-
if the wood is consistent in density etc etc,,you can cut it out and it will be tillered,, but wood usually has variations from one part of the stave to the other, then you have too look at how it is bending and remove wood as needed,,, part of the limb may react to the compression differently and start to take a set more than the other,, then it will need to be adjusted by eye,,,, not a caliper,, :)
-
Or make polycarbonate limbs with profile similar to what a bow's would be. Ala, 3",2", 1" tapering to 3/8".
-
Or make polycarbonate limbs with profile similar to what a bow's would be. Ala, 3",2", 1" tapering to 3/8".
Yeah, that's reasonable.
Any other offers? 4" to 3/8" ?
The more extreme the variation the easier it will be to see the change..
Maybe 4", 2" and 1" all going to 3/8 ?
Del
-
I gather the objective of experiment is to verify that "The curvature will not change by narrowing the triangle" (by Asharrow). If so, I think it would be easier to model just one limb and even simpler if you model one lengthwise half of one limb. That way you only need to cut one straight line differently for each test, leaving all other lines straight and perpendicular to each other. You can even use the same material for all tests, cutting it narrower for each test and recording the curvature. Good luck.
-
The purpose of the test is simply to see what curves result and which is the best approximation to an arc of a circle.
It can sometime be a mistake to assume the result before the test as it can lure one into misinterpreting the result to favour one's preconceived notion.
But in reality, I'm sure we all know what we expect to see :laugh:.
(My view is that narrowing the triangle WILL change the curve (but tell anyone I said that ;) )
We should each draw our expectations and seal them in a manilla envelope only to be opened when the experiment is complete in the presence of the Great Panjandrum himself! A gold star can be awarded to the closest!
(Sorry drifting off a tad there... better get back to cooking the chilli :laugh: )
I'm off on a shoot in Windsor Great Park tomorrow*... so I can't do it then...(hope maybe Monday)
Del
*We are registering for the shoot at the barracks of the household cavalry and they are going to arrange a cavalry charge at us!!! :o (We won't be allowed to shoot at 'em) I hope to get some video for the blog. (I'll be taking spare underware ::) )
-
this is all good and well, but with all the variables in a stick of wood I'm not really sure this experiment is really going to prove anything with regards to a wood bow
-
this is all good and well, but with all the variables in a stick of wood I'm not really sure this experiment is really going to prove anything with regards to a wood bow
Whaaaa?
That can't be right.
We can't all swan through life muttering mantras like.... "front profile dictates tiller" and "Pyramid bows should be arc of a circle " without trying to pin some of it down a bit.
How "pyramid" is Pyramid"? After all a parallel limb is just a 0 degree taper!
If we taper to zero thickness maybe it's automatically right.... but how wide do you start?
I'm all for practical rather than theory, but an empirical test like this could actually show us... how a simple board bow should be such and such taper )or thereabouts.
Sure, we don't have to all build 'em like that that, but knowing the optimum can help when we have to make compromises.
Mind, having said all that I take your point.... you can only use the wood in front of us.
Now look what you've done...
I'm arguing with myself...
No I'm not! ::)
Yes I am....
Del
-
Del I propose someone get a fully quartersawn board, any flavor will do, rip them into let's say 1/4" thickness's for four tests, then cut your front profile taper in diminishing widths, at least then you are using the same materials that the bows are made of, I know I've made a lot of board bows in pyramid style with the working limbs ripped on a tablesaw and they don't always have "perfect tiller" like mentioned in the bible's, seems like most guy's leave the last six or so inches stiff anyway so that kinda screw's the pooch as far as " front profile dictates tiller" and "pyramid bows are arc of circle" anyway, righhhhht
-
Oh Bubby, that's a waste of a perfectly good piece of wood. Nobody gives a hoot if we waste a chunk of plastic. Besides we're trying to prove an idea so we need the most homogeneous material we can find. Once we prove what a "perfect" material can do then we can apply our new-found knowledge to wood. Not that it matters, I'll still tiller by bend. :) :)
-
Sorry Del, I kept saying "we" as if I had something to do with this experiment. :-[ :-[
-
Sorry Del, I kept saying "we" as if I had something to do with this experiment. :-[ :-[
No no not at all... I want it be "WE" I'm cocky enough to think I know the answer, but it would be fun to get some pics... heck I could edge light the bows with disco lighting...
No point me doing something and then others saying' yeah but you diddn't do this or that.
Anyhow I should apologise for taking over the thread.
Should I put it up as a fresh topic?
Del
-
If you shine a torch (note the correct term) on one of the cut edges it will illuminate all other cut edges won't it?
-
If you shine a torch (note the correct term) on one of the cut edges it will illuminate all other cut edges won't it?
a fiber optic arc
-
Could be all the rage in Christmas decorations... :laugh:
I expect I'd need to polish the edges... we'll see. Maybe it will become an after Christmas project.
Del
-
Actually Knoll who started the thread can do the test for us, if he is willing to draw the curvatures meticulously on a sheet of paper by following it on a tillering tree after narrowing the triangle enough to be discernable. I would like to know what kind wood he has and how long is the stave. Once he reached his target draw strength but not his draw length, he can draw the line following the curvature of the limbs. After that he would be pulling less and less in poundage but same in draw length to matched the drawn line and see if the curvature stays the same even though the poundage is less and limbs are narrowed. He has to remember that the start and ending points of the lines should be same for all lines. I expect to see just one thick line.
-
If one wades through all my posts on this topic, I THINK it will be found that I reported Klopsteg et al as describing a limb that tapers to a point, modified to run parallel from where the lines reach the width that the nock needs to be.
So for your test, the taper should run right to the point, or aim for the point and stop narrowing when the sides are the width the nock should be.
BTW, just by way of disclosure, I have done this experiment with thin hickory slats with the results I expected. Your experiment should be even better because the material you plan to use is more uniform than wood. I look forward to seeing the results.
Jim Davis
-
My bow is hard maple. It's a Christmas gift and, being that we're well into Dec., there's no way I'm gonna commit it to an experiment. ::) Hopefully, it'll be "harvesting" forest rats next year.
It'll be interesting to see Del's results!!
-
To be honest Del I don't think it's worth bothering. We all know the answers! It really is quite simple as I stated earlier - thickness determines bend. As a material thins it can bend further. It's just common sense really. >:D
The theoretical pyramid bow with no thickness taper goes to a point.
I've pretty much always made my bows following the 'thickness rule' and the set that the bow takes is as much of an indicator as is needed.
-
If one wades through all my posts on this topic, I THINK it will be found that I reported Klopsteg et al as describing a limb that tapers to a point, modified to run parallel from where the lines reach the width that the nock needs to be.
So for your test, the taper should run right to the point, or aim for the point and stop narrowing when the sides are the width the nock should be.
BTW, just by way of disclosure, I have done this experiment with thin hickory slats with the results I expected. Your experiment should be even better because the material you plan to use is more uniform than wood. I look forward to seeing the results.
Jim Davis
Yes I can mark the taper to a point at the nock, but obviously it will have to be thickened locally and extended a tad to allow stringing.
Ah, I can see the caveat "tapers to a point" makes a big difference rather than just "narrowing the triangle doesn't effect the curve" The latter statement allows wider tips and was the subject of a discussion about thickness vs width taper of the working limb in a molly.
Maybe I can simplify the test to two extreme cases 4" tapering to zero and 1" tapering to zero.
Del
-
After reading threads like these I wonder how my dumb a$$ ever gets a bow to stay together.
-
Luck Pearlie, dumb luck.
-
After reading threads like these I wonder how my dumb a$$ ever gets a bow to stay together.
Pearlie, you are proably one of the best examples of why these discussions exist. I don't think anyone is consiously thinking about all these things when building a bow but if they have been doing it for a while they know the principles behind building one and the techniques they need to use. Your bpws pretty much conform to sound principles, you most likley picked up your style of building through experience and looking at other bows you liked.
When you are stepping way outside your comfort zone with either a style of draw weight this is where having some knowledge can come in handy. If you are new everything is outside your comfort zone. Luckily you will have plenty of examples of successful bows you can refer to and use as a refference.
Not all the rules we use have to do with stressing the wood, a lot of the rules relate to efficiency. Example s light stiff tips will usually outshoot heavy wide bending tips.
Most of the mantras that folks actually think about are because they make good sense.
" thickness determines how nuch wood can bend" "Width determines how far it will bend".
"tiller shape should match front profile" is saying the exact same thing as above. These mantras help to achieve even stress in the wood as best as possible.
Some of the interesting arguements come in about best possible performance when it comes to tillering and stress on the wood. I feel like too even of stress over too much a limb makes it easier for the limb to occilate and vibrate costing some efficiency. I can't prove it because I don't know how. Some of my fastest bows have not been good example of proper tillering.
I am building one right now for a lady, same demensions that I would normally use for a 70# osage except ths one is only 35#@28. The overall mass is comming out at about what I would normally expect from a 35# bow contradicting a lot of things I have said in the past. Bow is not taking any set and hopefully will be a good shooter.
-
Badger, is it because the mass of the piece of osage is more like hickory????
-
Luck Pearlie, dumb luck.
Guilty as charged Pat. Im just a hard-headed German guy that never stops trudging ahead until I get/see what I want.
-
My bow is hard maple. It's a Christmas gift and, being that we're well into Dec., there's no way I'm gonna commit it to an experiment. ::) Hopefully, it'll be "harvesting" forest rats next year.
It'll be interesting to see Del's results!!
Knoll, what I have described is just another way to do "no set tillering". Doing the "experiment" will help you make a better bow and it's the safer way to tiller than just trying to make the curvature look good.
But, we need to clarify one thing first. It appears that Del is assuming that we are going to reduce the width of sides evenly, thereby changing the proportions of the widths at fades and at tips. If we do that, of course, the curvature would change. We are assuming that we are going to keep the proportion intact when we say "narrowing the triangle doesn't effect the curve". If we also assume that wood is practically uniform, there is almost no need to do the experiment.
-
Yes, dead straight taper... all limbs same length ... no fiddle factors.
Simple is good with experiments. Fewest possible number of variables.
Del
-
Del, it would seem to me that the piece of plastic you triangled and bent will bend elliptically with the wider portions bending very little. Yes?
If so then that is precisely want you do not want in a bow because the outer portions of the limb, if they bend more, will yield more set.
Rather, the near handle, wider wood needs to bend more resulting in a more rounded circular tiller. Cuts down on set.
How you get there does not matter. Tiller edges, belly or a combination.
IMHO.
Jawge
-
I encourage lots of youse guys to make a test piece like this, clamp the wide end and and push on the pointy end. Even for those of us who have been making bows for years, it will be an eye-opener bordering on a jaw-dropper for those who have not tried this.
Jim Davis (who only makes "pyramid bows" because of this bending behavior.)
-
Remember it is a string gripped in the center that bends the limb, not a force pushing straight down on the tip.
-
Push diagonally then!
Asharrow is dead right.
It's all logic as Badger said above.
The experiment should be between two actual bows. One a pyramid taper and one with no width taper until say 8 inches from the tips. Tiller them both to take the same overall amount of set and just look at them at full draw.
Badger I agree that the more working limb there is the more the bow 'buckles' when the string hits home. This is another reason why Turkish hornbows are so fast.
Simple. ;)
-
I can't add anything to this discussion, but reading all you experts discussing tillering from first principles is really helpful for the likes of me who as yet know essentially squat about it but like to know the 'why' as well as the 'how' - so thank you!
-
Usually only do it when I am getting really close to what I want, little harder to take to much off the edge ;) so for fine tuning and final tiller I use it some. :) Interesting conversation going on. :)
Pappy
-
I'm not sure where you got the Info on side tillering pyramid bows, I've built a ton of them and don't think I've ever side tillered one, I start with an even thickness but buy the time I'm done tillering there's usually a silght thickness taper
I agree. Mine end up with almost no taper in thickness, but the thing I like about pyramid bows is that I cut the fron profile out and then don't mess with it. The very slight thickness taper sort of happens by default. For instance, I put maybe a slight trapezoid to the cross section, and smooth that in and I'm done.
If all your previous bows were simply tapered side to side in straight lines, like a long, skinny triangle, there shouldn't be room for much front to back taper. The regular bend of the consistent side taper isn't just good for bows, it is essentially an engineering principle. So, I'm puzzled, a little.
-
My bow is hard maple. It's a Christmas gift and, being that we're well into Dec., there's no way I'm gonna commit it to an experiment. ::) Hopefully, it'll be "harvesting" forest rats next year.
It'll be interesting to see Del's results!!
Lately this is all I make Maple Lam bows with a 20" power lam. About 1 3/4" fade down to about 3/8" - - - 1/2" tips. I do not touch the bellys nor are the lams tapered. I just taper them down, have to be careful where you start because of limb twist.
My bows take about 1" - 1 1/2" of set, and they are all stressed to over 29". Maple is very forgiving the wood fibers stretch more than most woods. ;D
-
Thanks, 101, for the post.
Fyi, I busted the $!*& bow shortly after getting to full brace. :(
I've got a couple maple bows and do like 'em. But haven't tried the lam route yet.
-
Alright mike. You have suffered enough. Come by the shop and I'll get you fixed up on a good stave to make a suitable bow from
-
Alright mike. You have suffered enough. Come by the shop and I'll get you fixed up on a good stave to make a suitable bow from
;)