Primitive Archer
Main Discussion Area => English Warbow => Topic started by: markc324 on September 16, 2016, 02:23:06 am
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Hi,
I'm new to archery and would love to learn more from all you good folks! I'm trying my hands on making a bow since I know how to build stuffs (self-taught mostly..) and am confident with my craftsmanship. The bow I am making is jatoba (brazilian cherry) backed with maple to sort of mimic the yew wood. I think I have the whole thing up to this point in pretty good, if not excellent, shape...I've rounded the belly, bevelled the edge of the backing, attached and grooved the horn nocks. Now for the scary part - tillering...as much as I love the way things turn out thus far, but with bad tiller, all these milestones will all come to the unfortunate failure. Please refer to the images attached to this post. I've added one original and one with my own diagram drawn to it. according to the diagram, i can see that the top limb (right) is bending a tiny bit more then bottom limb (left), which is ok as long as it is within ⅛" - ¼" (i've read this somewhere. please correct me if I am wrong on this). Please provide your input and thoughts on the current tiller. Feel free to add your own diagram to the original image for analysis, and also, much appreciated if you guys can give me some pointers on what to do next.
I should also mentioned that the bow is having a low brace right now, 5" to be exact, and has not bent past 6-7 inches so far. at this point, is it safe to brace to 6.5" brace height?
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can you guy see the images attached? it shows up on my computer, but not my phone nor my wife's computer. I wonder if you guys are experiencing the same thing.
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Your bow has far too much bend in the middle, and none anywhere else.
At such an early stage, you want the midlimbs to be doing most of the work, as the middle only starts bending towards the very end of the draw. The further you pull a bow, the more the middle will try and bend so if you were to take your bow as it is now and draw it to 30", you'd see a massive hinge smack in the middle, and stiff limbs everywhere else.
You can keep it at the current brace height if you want, but work only on the mid-limb to tip section on both sides. You're going to lose a lot of draw weight and take some set but that's how you learn!
What I would do personally is unbrace, reduce the limbs and then brace it again, and keep repeating until the brace shape shows an even bend in the midlimbs and much, much less bend in the middle. Then start drawing it on the tiller and make sure the middle doesn't do any more bending until at least 20" if not more.
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What 'e said: I'm no expert, but that's not bending all over like it should, it's all in the middle; mid limbs and tips need to start bearing some working load.
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Looks like you might have the beginnings of a hinge right where it sits at the door jam.
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Dunno if I'm not understanding but it seems you are trying to make a bow first and then pull it.
It doesn't work like that! (others may tell you different)
You have to work with a target draw weight and draw length. Pull it to your target draw weight as long as there isn't a problem like a weak point or it is bending unevenly), you then look at the draw length, if it's not drawing far enough you then remove wood from the belly and try again.
So typically you'd get results like this... assuming you want say 100# draw weight at 32"
You pull 100# and it comes back 12" you remove wood, to adjust the tiller and try again, it's then
100# at 13" you remove a little more, improving the tiller.
100# at 14", you increase the brace height to a full 6" and try again.
100# at 14" still, you take off more wood...
and so on until you get to 100# at 26", you then start really narrowing the tips fitting nocks and bringing the tips round the last little bit.
100 at 30"... you quit there, as it will settle down to 100 at 32" once it has been shot in.
It is doubtless possible to build a bow by numbers (especially a laminate) and just take it to full draw... it doesn't mean it is a good idea.
With a warbow it hard to get to initial brace, if it is easy, you will probably find you end up with a 70# bow not 100#
Del
PS. Not sure if this post from my blog will help, it should at least provoke some thought.
http://bowyersdiary.blogspot.co.uk/2013/12/yew-stick-bow-and-draw-weight-to-brace.html (http://bowyersdiary.blogspot.co.uk/2013/12/yew-stick-bow-and-draw-weight-to-brace.html)
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as Del has implied, doing the finish work before seeing if the stave will become a bow, is a way to set your self up for disappointment if all does not go well.
Seeing the correct bend at 6" is not a skill that comes easy for many, and I certainly ruined a few pieces of wood while learning.
One possibility you might consider, would be to rip a 1/4" slat and side tiller it so that it has the final shape you desire at full draw. a true arc of a circle at full draw might be a good place to start for a warbow. comparing curves of your model to the jatoba laminate, at lesser draw lengths, will give you some reference to work from.
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Don't panic, your only at brace height and there is plenty of time to get the bow bending in a more even way!
What normally happens is that by floor tillering or using a long string, you are able to check the bend before reaching brace height.
You can't always rely on the bow being worked down to what you think is a correct taper and then bringing it to brace.
I don't think the tiller shape you have at the moment is a problem as long as you don't have any crystaling.
Your next step is to mark the areas that need to start bending more and reduce them slowly in order to get the brace height tiller to be a bit more even. However, don't bend it beyond 7-8 inches in-order to achieve that.
The main lesson to learn here is tillering starts as soon as the stave is flexed!
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wow, thanks for all the good inputs! i've actually absorbed and digested a good amount of it before continuing the work session this morning.
one thing i want to mention, though, it that I didn't actually "made" a bow first and then tiller it. the wood is actually very rough. I just rounded the belly and the edges of the back so it will start to bend, but it needs a lot more shaping here and there. as for the horn nock. I admit it really isn't the stage where they should be added, but they are only glued on (with Del's 6" mark on masking tape trick i learnt from youtube!) and more shaping is required. Sorry if I scared any pros out there and made you think i backtracked on this project!! ;D
here is the image as of the end of the tillering (or more of a workout for me)...
currently it is at 70# @ 30". my target is 70# at 32" (i am 6'2"). I took it nice and slow; giving it 30-40 repetitions of pull before I move down to the next inch of draw, and then repeat the 30-40 rep exercise.
at current state, it is not showing any chryshal mark or cracks. Bow shows 1.5" of set/string follow but relaxes to 1.25". How does that look for a 74" NtN bow with such draw weight? Both limbs are bending very equally. I divided each limb to ⅓'s and measure the distant of belly to string and one side matches with the other dead on, no + or -!
To my inexperience eyes, i think it is a good outcome for the first bow, but I believe it is by no means perfect and I still have much to learn. I can see tiny gaps between the limb and the blue circle i drew. I will refine that as I finish it up in the next couple of days (definitely taking my time on this project).
please see the images and share your comments and suggestions of what to do from here. Much appreciated!
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nice smooth bend, I am watching with interest to see what advice you get from the pros about the last two inches.
Have you shot it much at 30"? I might be tempted to shoot it in some, before final tillering/sanding.
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thanks, definitely happy with where it's headed!
if what I've leant on my own search on internet is true. the last 2" doesn't really bend, do they? I remember seeing videos about sanding through the sap wood growth ring of yew around that area for his own reason, and the bowyer mentioned there's practically no bend there; but he also mentioned that he knows what he's doing and should never go through growth rings anywhere else. Im anxious to see what the pros will comment on that, too.
I haven't shot it in yet; mainly because my arms are tired after a whole day of workout. I'll be training the bow to shoot either tomorrow or the day after.
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there is a lot I have to learn about warbows, let alone yew, so I can't comment on the "no bend" thing, but jatoba could be entirely different. My thought was to shoot it some and inspect closely for chrysals and tiller change for a while, perhaps have someone take a photo of the bow drawn in the hand to compare with your photo on the tree.
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look what i just found out!
the previous image with the blue "circle" was and ellipse. I accidentally compressed it up-down direction without noticing and i just noticed it now. I changed it back to a circle and the last two inches mentioned by Willie all of the sudden appears to be pretty close to the arc!
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i see now that you are referring to the tips as the last 2", and yes, they really do not bend that much.
I was speaking to the fact that your tillering stands at 70#@ 30", leaving some small reductions undone to make weight at your design pull of 32".
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Willie makes a good point about shooting the bow in a bit before sanding and finishing.
I think Asham makes reference to shooting the bow in and then returning it to the Bowyer to 'Pike', which may mean putting on the horn nocks.
Anyway, your bow is looking great!
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I would shoot it a bunch, couple of hundred shots, before doing anything else. You may find that after shooting it in that it will be 70#@32.
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I was speaking to the fact that your tillering stands at 70#@ 30", leaving some small reductions undone to make weight at your design pull of 32".
Haha, sorry Willie. don't know why I misunderstood it
I light sanded the limbs a bit this morning and then re-check the tiller; it was still fine, so I took her out to the local range. All the archers were thrilled to see the handcrafted bow! I was a bit embarrassed because things could still go wrong with it as it needs to be shot in, to be trained to shoot.
I put 50 arrows through her and she managed to handle that pretty well; no chryshal or splinter raised. My goal was to put 100 arrows through her, but being she is a 70lb'er and with a whole day of tillering workout yesterday, my limbs are much weaker than hers today......
there were two archers I met when I was on my way out of the range. We chatted a bit and became friends. They were generous enough to help me train the bow some more!!
here is a pick showing the tiller after 50 arrows, and surprisingly the set/string follow reduced to just 1" end of today?? it was at 1.5". I've always heard of set increasing but not reducing is this normal?
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If you weren't drawing the bow as far as on the tiller tree it could easily show less set after shooting.
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If you weren't drawing the bow as far as on the tiller tree it could easily show less set after shooting.
i'll look into that. I'm not sure about the two archers who shot some arrows, but for the first 50 arrows shot by myself were pulled to full 30", and I used the 30" arrows so I know if I've drawn it far enough and not over.
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There are two things, set and string follow.
Set is permanent, string follow recovers after a few hours.
So after a full days shooting you may easily have 1.5" next morning it will be back to 1".
There is a lot of hysteresis in the wood.
Del
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nice work!
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I'm surprised nobody has said but next time forget this 'true arc of a circle' tiller for elbs' Your tiller should be more elliptical. Elb's taper in thickness. Wood at any given thickness can only bend so far. As wood gets thinner it can bend further. If thicker it can only bend less. Put all that together and apply that thinking to an elb and you have an elliptical tiller. I still think the handle is bending a little too much and mid limb out should be bending more.
The wood will have told you! If you look at where on your bow the set is you get a definitive answer on tiller that is never wrong!
Anyway well done on making a working bow ;)
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I hope nobody construes "a true arc of a circle at full draw might be a good place to start" as being a given for all elb's. I make no claims to being an authority on elbs, and gladly defer to those with more experience across the pond. The uniform bend idea was suggested as a possible way to hone tillering skills.
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FWIW some of the best bowyers in the world specialising in "true" English warbows/longbows and responsible for numerous records tiller their bows to a perfect circle.
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FWIW some of the best bowyers in the world specialising in "true" English warbows/longbows and responsible for numerous records tiller their bows to a perfect circle.
Good for them. ;)
As wood gets thinner it can bend further before taking set. There are ways to prove this scientifically but simply watching set will tell you that an elliptical tiller is correct for any elb 30# or 130#. If you think about it it is quite obvious really ;) I guess where a lot of people get hung up is on the amount of progressive bend needed - it isn't a huge amount. I suppose it is easy to think in back and white when actually we are talking about shades of grey.
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mike
does this progressive bend add anything to the performance or handling of the bow? could you point to a photo that exemplifies this nuance of tillering?
thanks
willie
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Bend a small piece of wood and it will return to shape. Bend a massive piece of wood and it will break long before it bends much at all.
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We talk a lot about bows bending in an "arc of a circle" but the only true way to do that without the bow suffering undo fiber stress (exploding) is to taper a bow's width with a constant thickness. Whenever the bow's thickness is tapered, it will always bend into an ellipse provided that the fiber stress is even along its length.
Remember: R/T = E/2S
Where:
R = radius of curvature
T = Thickness
E = Modulus of Elasticity
S = Modulus of rupture
Your bow looks fantastic to my eyes.
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Wooden Spring
"it will always bend into an ellipse....." seems like a bit of an absolute. I was under the impression that if the thickness taper is too litttle, then the bend happens more at the handle, and if too much, then more bending happens towards the tips. Isn't there a thickness taper that gives the circular bend? Of course we often taper both the thickness and the width, and I am sort of partial to a constant thickness taper, where the tips are 1/2 the thickness of the handle, combined with some width narrowing in the outer third of each limb,at least for a bow that is 2.3 longer than the draw length, as over drawing and under drawing seem to change the relative shape.
willie
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Wooden Spring
"it will always bend into an ellipse....." seems like a bit of an absolute. I was under the impression that if the thickness taper is too litttle, then the bend happens more at the handle, and if too much, then more bending happens towards the tips. Isn't there a thickness taper that gives the circular bend? Of course we often taper both the thickness and the width, and I am sort of partial to a constant thickness taper, where the tips are 1/2 the thickness of the handle, combined with some width narrowing in the outer third of each limb,at least for a bow that is 2.3 longer than the draw length, as over drawing and under drawing seem to change the relative shape.
willie
Well, we live in a universe governed by laws, whereby everything that moves, moves according to universal and absolute principles established at creation, and mathematics is one of the tools that we have of making sense of those laws - the structure and motion of an archery bow are just as absolute as the laws of thermodynamics.
One may well get a thickness tapered bow to bend in the arc of a circle, but the inevitable result will be that it will suffer uneven fiber stress. It is the reason of uneven fiber stress that is why a Welsh Long Bow is not the most efficient of bow shapes. This is not to say that it isn't a "good bow," it's just not very efficient.
A bow's thickness may be obtained by
T = [(2S)(R)]/E
Where:
T = Thickness
S = Modulus of Rupture
E = Modulus of Elasticity
R = Radius of curvature at a particular point along the limb
It's width may be defined by
W = (6PD)/(S)(T)(T)
Where:
W = Width
P = Tension in string (about 12% more than draw weight)
D = Distance in inches from the fade to the string measured perpendicularly to the string at full draw
S = Modulus of Rupture
T = Thickness
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yes, if we also want to have a bow with constant fiber stress, then limb bend shape is dictated by thickness. There are also places along the limb where we might want to have less than max strain. I am thinking of many designs where it is desired to keep the center and/or the tips bending slightly less, especially during the tillering process. These stiffer areas can be said to have less strain. Are you looking to build something like the ELB presented above? I recall you working exclusively with constant thickness pyramids in the past? The design I posted above,(tips @ 1/2 the thickness at the center of the bow) allows for a mid handle strain that is 90% of the max strain at midlimb. I by no means claim to know much about ELB design or tillering, and suggest the taper as a starting point for development. Perhaps some of the bowyers from across the pond would be willing to offer descriptions of tapers used in established designs. If I remember correctly, I have seen designs that start the width taper closer to the handle area, and so may not have a straightline taper in thickness, but perhaps reduce the rate of taper out towards the tips.
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When I was making a lot of ipe elbs my width taper was - 1" wide parallel for the 4 inch handle and 4 inch either side (12" total parallel width), then taper to 3/4 inch 12 from the nocks then taper to 3/8th at the nocks. 72ntn bow. My thickness taper started directly from the end of the handle to 3/8ths at the nocks.
I would make the tiller a little more elliptical and the handle stiffer on the lower weights.
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Wooden Spring - well said :) At the end of the day any piece of woods thickness determines how far it can bend all other things being equal. In our field watching set is the laymans way of 'seeing' the fiber strain.
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Wooden Spring - well said :) At the end of the day any piece of woods thickness determines how far it can bend all other things being equal. In our field watching set is the laymans way of 'seeing' the fiber strain.
Absolutely, and don't forget that while we are watching set as an indicator of fiber stress, since most woods are stronger in tension than they are in compression, one can always reduce set by narrowing the back of the bow about 10-15% of the belly width.
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Again I agree totally. I see very few bows with trapped backs. I also think this is a major factor in a lot people being 'down' on woods like red oak, ash ect trapping these woods enough makes a huge difference to the set in the finished bow. I started making my ash (fraxinus excelsior)bows with backs about half the width of the belly just to see if they would fail in tension yet they never did.
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Might be good to have a D cross section with "meane" wood bows, but with the back rounded rather than the belly..
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That's done quite often with heavy meane wood bows, in particular hazel and plum. Even woods like elm respond well to the reverse D section, however.