Primitive Archer
Main Discussion Area => English Warbow => Topic started by: William M. on March 04, 2021, 06:44:15 pm
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Hello everybody!
I am trying to make an 80# ash Longbow, but since I am a beginner and this is my second try I feel really nervous tillering it. My first attempt with Black Locust didn´t go well(I cut all the growth rings on the back) and now I feel really uncomfortable tillering this one. :-\ I would like to ask you what you think about it and maybe some of you experienced Bowyers can give me some advice. I would really appreciate it. :D
Thank you.
Measurements right now: 72 inch long, 36mm wide and 34mm deep on the handle tappering to around 20mm
Here the video of my tillering, but I am not sure where the weak spots are: https://vimeo.com/519715852
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Looks ok but you need to pull it either further to 80# or simply remopve wood everywhere if you are already pulling it to 80#.
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Make sure the thickness taper is even by feel with your fingers. That will tell you more at this early stage than trying to visualize a small amount of bend on a stave with character.
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Thanks for all the tips :D
I heat treated the belly before so I gonna have to wait a few days I think, till i can start tillering again
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Make that tillering string shorter... it should hang down no more than 6" absolute max... shorter the better.
Del
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Thanks for the tip, sir! I didn´t know that. Gonna start tillering tomorrow again I think. Is waiting 2 days after heat treating enough?
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Yes it will be fine to work on.
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Okay thanks!
Another question since I am using a 16 Strand string for tillering. Should I use a stronger string for 80+#?
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Should be fine. The problem I ran into with my B50 strings was that they stretched a ton on heavy weight bows.
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Thanks for the tip, sir! I didn´t know that. Gonna start tillering tomorrow again I think. Is waiting 2 days after heat treating enough?
Overnight is fine.
Del
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Okay thanks!
Another question since I am using a 16 Strand string for tillering. Should I use a stronger string for 80+#?
That's fine for a Tillering string... most force on a bowstring is when the limbs slam home at the end of ashot... which doensn't happen with a tillering string.
Del
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Thanks!
Still feeling anxious tillering it since the last one exploded :-\
Gonna aim for 80#, with a nice tiller to have at least one success feeling ;D
Gonna try to use a 16-18 strand B50 string
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Been tillering for the last couple of hours, bending till brace hight now at around 100#.
Can I low brace it with a 16 strand too? Or should I use a 18 strand?
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you are aiming for 80# finished weight? your choice of final draw weight should not exceed whats possible based on the dimensions of your stave. your 36 mm dimension stated earlier may well be ok for the proposed 80#, but not for more. I don't know myself, as I do not know much about the ash you are using.
during tillering, a lot of guys make it a point to never pull over intended finished weight. this advice is especially prudent for beginning bowyers.
even when you reduce some more so that 80# gets the bow to brace height, that does not mean it is time to brace. early bracing often causes a bow to be overstressed. at that point, you might try to shorten the string to the "as short as possible condition" until the tips are brought back to 8 inches or so (pulling 80# of course), then up date your video. we like pics :)
now is a good time to trace an outline of the back of your rested stave. it will be useful later to compare with if the bow takes some set in the later stages of tillering.
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Thank you very much willie! I was getting "overmotivated ;D Yes I should stay at the 80# max. as planned.
Here are some pictures from today and a video tillering. This is after heattreating the belly. I was slowly taking more and more away, but still in small steps. Maybe I gonna finish tillering in a month or so haha
The video: https://vimeo.com/520426850
On the left side it´s uneven, first I thought it´s a knot but it isn´t. It seems thick from this side but on the other side its thinner because it has a light twist on this limb. Not quite sure if it´s a weak point or not.
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william, the video did not work for me but the first one did.
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Really? For me the link works. :-\
I gonna re-upload it later
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With that little amount of bend I’d still have it at the floor tiller stage. Looks like it’s bending more in the handle and inner limbs. If you’re pulling it on the tiller tree make sure that the bow is balanced with the tips even with the handle. Looks like it’s sitting at an angle with the left tip higher than the right.
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I have taken more away qith the rasp since it's already at 80# while not bending at all. I guess I have plenty of room taking more wood away. Its around 31mm in the handle now I guess i can take it to 29 at it should work :-\
It´s weighing around 1100g now
This is how it looks now.
Video: https://vimeo.com/manage/videos/520606672
The right outer limb might be stiff and the left middle one. What do you think?
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Its a bit hard to tell until its bending more. If it is bending more in the center at this point I would be cautious about removing too much from the middle at this point
removing materiel from the middle third creates more apparent tip deflection, but will get you in trouble later, thats' because the bow will want to bend more at the handle than anywhere else when you get it out towards full draw.
find a pic of a well tillered warbow at brace for a reference curve. how thick are the tips? somewhere around 1/2 of the 31mm? the taper needs to even from center to tip at this point.
another trick is to draw an ellipse on a piece of cardboard for reference. do you know the string and nail method for drawing one out?
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Okay I gonna stop taking away in the middle section.
Tips are 2mm wide and around 1,7mm deep.
Is it to put a nail on one side and a pen on the other to draw a circle?
And thank you really much for all the tips and help!
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New video, now I shortened the string like Del recommended. Removed a bit more wood.
I dont know but the left limb looks stiffer even though its looking thinner. I dont trust my eyes anymore 😅
Video: https://vimeo.com/521042282
Should I take more wood away from the entire stave or should I focus to being down the outer limbs more?
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If you're trying to judge the bend by pulling that quickly while tillering then you need to slow down. No reason the bow can't be held for a moment to judge the bend. Hard to say from the video because of that.
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Okay I gonna retake the video tomorrow.
I was just think if I puöl it fast I may notice weakpoints, where its bending first or bending too much too early. Maybe my thhought process is wrong when tillering :-\
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if you draw your ellipse such that the vertices, or the P to Q distance is 120% of the NTN. (86.5" for a 72" bow), the curve will give a bend that is slightly stiffer in the handle. :OK
this can be a flat very flat ellipse, say one that resembles the bend half way to brace or more. I draw many ellipses on my backboard to compare with occasionally as I tiller out. but getting the right bend at about brace height makes the rest of the job go much easier.
The 120% makes a very nice shape, but you will have to ignore the last 6" or so on each tip. let them be straight and not bend around so much as the ellipse.
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if you draw your ellipse such that the vertices, or the P to Q distance is 120% of the NTN. (86.5" for a 72" bow), the curve will give a bend that is slightly stiffer in the handle. :OK
this can be a flat very flat ellipse, say one that resembles the bend half way to brace or more. I draw many ellipses on my backboard to compare with occasionally as I tiller out. but getting the right bend at about brace height makes the rest of the job go much easier.
The 120% makes a very nice shape, but you will have to ignore the last 6" or so on each tip. let them be straight and not bend around so much as the ellipse.
Yes, nice... but that's the problem with ellipses... just how much ellipse? Personally I'd prefer it a bit less flat (e.g more circular).
It would be nice to get some sort of consensus on what is considered optimal.
Of course the other problem is how far round the ellipse do you expect the bow to follow... obviously not right round to the horizontal line PQ, but the shorter the portion of the ellipse that is chosen, the closer it becomes arc of a circle.
Like I said very hard to define what we actually mean by "elliptical"
I've drawn a circle matched reasonably to the ellipse, up to the point where they intersect... it shows how subtle the difference is over a realistic arc.
Del
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I think the important part is having the right radius of curvature at any given point given it's width and distance from the limb tip. On a pyramid bow this should result in a constant radius which means it will have a circular arc shape.
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I think the important part is having the right radius of curvature at any given point given it's width and distance from the limb tip. On a pyramid bow this should result in a constant radius which means it will have a circular arc shape.
This isn’t entirely true but a close approximation. Here’s a post by Woodbear on Paleo Planet from years ago. Without getting technical it’s much easier to just monitor for set and adjust tiller accordingly.
I suppose it depends on what you call a pyramid bow. If the sides absolutely must be straight line taper, then uniform thickness is not going to give you circle of arc tiller, or uniform stress either. In order to get uniform stress and that perfect circular tiller the sides of the pyramid must bulge out a bit. The bow can and should taper as though aiming to get zero width at the nock, but then deviate from this shape and stay at a reasonable width for the last few inches prior to the nock.
A straight line taper to a point with uniform thickness is indeed the shape that gives uniform stress, and a circular bend in a cantilevered beam with a load at the end. But this assumes that the total deflection is small, such as in an architectural building application. The strength of the beam must be proportional to the distance to the load, and the thickness is the same for the length of the beam, so the width of the beam must be proportional to the distance to the load.
However in a bow the bend is large, and the bending force in not proportional to the distance along the bow arm. The bending force is proportional to the distance from the drawn bow string to the bow arm. Since the bow is bending in an arc, the force is not exactly proportional to the distance along the arm. (Note the difference between the straight dotted green line and the bow arm in the diagram.) In order to get circle of arc tiller, and uniform thickness, the width of the bow must be proportional to the distance from the location on the bow arm to the string at full draw. (This assumes a rectangular cross section bow arm pyramid bow.) This is called Hickmann corrected in archery the technical side. If you know the length of bow, and stiff handle you want, you can draw this out to scale on paper, and measure the distances fairly easily. Then use these widths when you lay out the bow. The maximum width of the bow should not make any difference to the need for a convex bulge to the sides, except that the width effects the draw weight.
If you want a pyramid bow with an absolutely straight taper, and also a circular tiller, you will have to adjust the thickness so that the bending strength of the bow arm is proportional to the distance to the string by adjusting the thickness instead of the width. The stress will not be uniform, being greater by the amount that the wood is thicker along the bow arm. If the bow tapers to a non zero tip width, then the tip area will be stronger and deviate from the circular tiller, but this seems to be advantageous most of the time.
I hope this satisfies the desire for a scientific explanation of pyramid tiller, and uniform thickness. The Hickmann corrected pyramid bow is quite elegant in its simplicity of concept. I hope I have conveyed it adequately.
Dave.
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I wish I had that book.
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Wow interesting things. I gonna read more into that.
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the ellipse shown in the post above is an example of how to draw one. It is not intended to represent any particular shape related to bows.
Yes, nice... but that's the problem with ellipses... just how much ellipse?
Del, I reviewed data collected on many of the mary rose warbows and averaged thicknesses widths and lengths to construct a "typical" example. I then entered the dimensions in a spreadsheet program to look at the bend profile and found a slightly stiffer handle area. The bend, at any stage of tiller, from a few inches to full draw can be fairly well seen in an ellipse with a major axis length 1.2 times as long as the nock to nock distance of the bow.
The height of the ellipse, will of course, vary with the stage of tiller. A flatter ellipse needed to judge the bow at brace height, etc.
As you note, some prefer a rounder full draw bend, but knowing what the braced bow bend should look like with out having built a lot of bows by the trial and error method is difficult to anticipate. I do know that many who set out to build warbows will often end up with a bow that bends too much in the handle. I have offered the 1.2 as a reasonable reference for a beginner asking for advice.
Of course the other problem is how far round the ellipse do you expect the bow to follow... obviously not right round to the horizontal line PQ, but the shorter the portion of the ellipse that is chosen, the closer it becomes arc of a circle.
The 120% makes a very nice shape, but you will have to ignore the last 6" or so on each tip. let them be straight and not bend around so much as the ellipse.
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willie, what would you recommend according to my last video? Should I take more away on the entire bow?
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William,
I am in agreement with Ryan, in that I find it hard to see well what is happening in your video. I do believe if you have something drawn out on a backdrop behind your tiller tree, it will be useful. I find when I tiller, I have to look at it multiple times and in different lighting.
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Okay thank you! Today I had no time working on the bow. Tomorrow I gonna use the string and nail technique you wrote a few days ago. Maybe I gonna put a light directly over the tillerboard. Since the light right now is not in the middle of the tillerboard and throwing a wrong shadow on the bow
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Willie, that analysis of replica dimensions sounds super interesting. In your diagram is f1-f2 the nock to mock length?
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Willie, that analysis of replica dimensions sounds super interesting. In your diagram is f1-f2 the nock to mock length?
No, the diagram is a generic illustration of how to draw an ellipse.
there is a bit of trial and error in locating the nails for any particular ellipse, But in this example for a shallow ellipse, I would proceed as follows.....
72" nock to nock distance times 1.2 is 86.4"
draw a line 86.4 and find the midpoint at 43.2" from the midpoint measure out 42? inches each way and locate your nails. your string will need to be 86.4 long. it should draw an ellipse enclosing the line. The center 60" of one side of the ellipse is all's that's needed. you only need the center 60 " because the tips need to be stiffer and not wrap around the ellipse all the way.
the arc will be shallower if the nails are further apart, and deeper if the nails are closer together. but the 1.2 factor holds true fairly well for a bow that is somewhat stiffer in the handle area, whether representing a shallow brace or closer to full draw.
A more bendy handle will be an ellipse of different proportion to the nock to nock length.
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How did you come up with the 42” from 43.2? Is there a ratio you follow? Seems like shorter bows of the same draw length would need a more circular shaped ellipse.
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ryan , 42 is just a guess for creating a shallow curve, maybe less than brace even. You just move the nails in to generate a curve that will match the bow at a longer drawlength. a shorter bow will have a different major axis length ellipse.
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Regarding the post about Pyramid taper. (We all realise of course that a warbow isn't a pyramid bow)
Not sure I agree with the mathematical analysis!
You have to remember that maths is a tool to explain reality...not the other way round!
I reckon any mathematical analysis of a bow is a series of compromises and simplifications.
Let's just look at a real life test:-
https://bowyersdiary.blogspot.com/search?q=pyramid+taper+test (https://bowyersdiary.blogspot.com/search?q=pyramid+taper+test)
Can you really see or measure any deviation from arc of a circle?
Mind TBF
Having reviewed the Mathematical analysis a bit closer I see two huge difference.
1. The Mathematical analysis include a stiff grip section (yes ok... that's actually far more realistic)
2. the work was done by Hickman! I'm a great fan of Hickman therefore I beieve it! ;D
It rather reminds me of the story about the mathematician and the engineer in the bar. They are 32' away from the bar.
The mathematician bets that the engineer can't get to the bar if he moves half the distance towards it each time he moves. The wager being to buy the beers.
The engineer accepts the bet, despite knowing that theoretically he will never reach the bar.
He walks 16'...then 8'... then 4'...then 2'...then 1'...
Having moved 31' he calls to the barman, reaches out his arm and picks up the beers.
It just shows that close enough is good enough for many real life applications. ;D
Some very good discussion on this thread.
I especially like Willies's work with the Mary rose averages :)... but is "slightly stiff at the grip" the same as "elliptical"... >:D (shut up Del!)
Del
Please note: I always reserve the right to be wrong!
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I'm starting to understand the Hickmann adjustment better. The bit about the cantilever beam is what I was thinking of when I said that the bow should have straight sides, but I didn't account for the component of the force pulling the limbs inward, only backward. The component inward would be cancelled out on a straight cantilever beam, but not on a bending bow. I need to figure out more math before I can quantify this.
This all makes sense because if you sharply bend a straight slat between your hands you get most bend in the middle, whereas if you bend a straight cantilever beam you get most bend and the base.
This would imply that bows with greater bend should have more mass in the center. Think of the west coast paddle bows.
I'd like to figure out a way to find width as a function of distance from the handle for any given bow, assuming a flat limb, so that the stress is uniform across the limb.
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re: limb taper
the post linked below shows the width and thickness tapers of the "bow" I profiled in the spreadsheet and fitted the 1.2 x ellipse to.
http://www.primitivearcher.com/smf/index.php/topic,61640.msg862289.html#msg862289
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Del, Certainly those polycarbonate bows are close. Close enough for a pyramid taper to be "practically" even in thickness taper. I do notice some irregularities in the shape. Looking at both photos, one limb appears stiffer in the outer limb as indicated by Hickman. The other appears weak almost mid limb with more space between the circle and the tiller at that point (not sure what's going on there). Could be asymmetries but the point was not if it was practical or not, just that it's not entirely true that a straight profile will result in a perfectly circular tiller in a bow limb.
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I think you can fit a better circle to the top one... ;) (I'll do it if you like)
But I'd like to see the corrected pyramid fitting better!
Del
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The radius of the circle is half the length of the bow?
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No, the circle radius is unrelated, it changes based on how far the bow is drawn.
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She is going to be a shocky number with that tiller.....too round in the middle third for sure.
These bows taper in thickness...right?
A thickness taper indicates an elliptical tiller because as the wood gets thinner it can and should be bending further :) Simple :)
I can guess where the set is on this bow and where it isn't :)