Primitive Archer
Main Discussion Area => Bows => Topic started by: willie on October 24, 2015, 02:18:31 pm
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I glued up a soft maple backing to a piece of doug fir or larch in an elb design.
It is presently 75 in nock to nock and 1.25 wide at handle with 3/4 glue in reflex
the belly wood has an S.G. of .69 @ 12 mc, which I calculate to be about .6 oven dry.
Never used a wood like this on a bow before, in fact this would be my first elb/warbow style bending handle laminated bow. I often hear that the elb/warbow is typically a highly strained design.
Having missed weight on a few bows in my time, and shooting for the most weight I can with this design..
How do I set a weight goal? any guesses where to start with thickness?
I hope to use Badgers "no set" approach to monitor set
thanks
willie
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Willie, I'm not sure how strong soft maple is in tension or larch/fir are in compression so it may not work at all for you. An ELB will need compression strong wood for sure. You'll be building an ELB but not necessarily a war bow.
If you never draw the bow over the draw weight but draw it to the desired draw weight you should be able to reach your desired draw weight. Reduce the belly until you get both limbs bending evenly and together at your desired draw weight. Unless your belly wood is over an inch thick, don't worry about the thickness, just remove wood until you get where you are going.
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Willie, get the bow bending evenly at floor tiller then take the physical weight of the bow, it should give you a pretty good idea what to expect out of it. If you are looking for say 75##30" You would need at least about 20 oz and that would be with a full arc of the circle tiller.
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Thanks Pat
I realize it may not work at all, and as I mentioned in an earlier thread, this bow is an experiment in many ways.
I fully understand that soft wood like I have will not get me into warbow territory. I guess that this bow is a test bow for seeing what I can do with the wood at hand for something bigger in the future.
I am hoping that the soft maple back will be stronger than the conifer belly,
I could pick a ridiculously high draw weight like 90# to start? and see if I could get it to brace without loosing my reflex? Thats my problem. with so many unknowns, estimating a reasonable goal.
I have found that having weight too high to start with, and constantly changing my goals leads to a bow that is "tillered to death" if that makes any sense
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Badger-
I need to get the belly down some more to floor tiller, and floor tillering at these weights is new to me.
I think that I will compare floor tiller to two of my 40# held at once, and then weigh the stave.
thanks
willie
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When I hit floor tiller I'm probably 20# to 30# over draw weight(just a guess). By the time I get to low brace I'm about 10# over draw weight. As I remove wood and exercise the bow I slowly draw it to my intended draw weight or just below it and check the draw length. From floor tiller I also just use a scraper and rarely a fine rasp when needed. Taking it slow, exercising the wood and watching for any string follow is the way to go. If your bows are taking excessive set you are either using unseasoned wood or over stressing the wood.
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Pat
I slowly draw it to my intended draw weight
I follow what you are advising as a method to reach weight when you know what weight you want, and suppose most people start with a plan for a particular draw weight in mind
My experiment with this particular bow is to see what this wood that I have never used before is capable of, weight wise, and monitoring set is of course the way to go. I guess as an relatively inexperienced bowmaker, I find it hard to judge set taking "as you go"
Willie
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If you are using a tiller tree put a paper background behind the boy and draw a pencil line along the bows back on the background. After you have progressed a bit compare where the back is in relation to the last time. If the difference at the tips is more than an inch or so you are possibly overstressing the bow while you build it. You have to educate the wood to not only bend but recover also. If you trace the outline of the back at each wood removal you can see just where the limbs are taking set and adjust your tillering accordingly.
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just get the bow bending even,, once you can brace it,, get the tiller even and there you have it,, whatever you have will give you a starting point for the next bow,, :)
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Willie, if you want to find out what the bow is capable of standing mass weight will give you a good starting point. Now you are working with two woods that are not generally considered bow woods. If the wood is .69 sg it more likely to be larch than doug fir even though they look alike. I don't know the qualities of larch at all. I would assume it to be similar to cedar for my experience with it working arrows. For example if I were working a suspect wood I would probably add about 4" the the draw length I used in a mass calculation. It might not be necessary but I don't think anyone is very familiar with larch as a bow wood. I would say see how much it weighs and then go from there. If you start pulling on a wood with no idea how much it can stand you are just guessing. Sometimes it works sometimes it doesn't.
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thanks for checking in occasionally, I spent a little time smoothing the back and I am still "floor tillering".
since I cannot bend and look very well, I set up two milk crates with a bathroom scale on it.
pushing down on the handle with the tips on the scales, I read 40# on each scale (pushing 80?), to get 5 " bend
I lost 1/32 of my reflex doing this and the bow weighs 23.6 oz or 700 grams
your thoughts are appreciated, as I have never tried to tiller this high a poundage bow before
willie
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If it weighs about 23.5 oz and is just starting to flex it will likely go down to about 20 oz. If you decide to go 40# I would make the middle 12" of the handle area just barely flexing and tiller slightly elliptical from there. If it won't hold up at those dimensions it is just not good enough bow wood.
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Badger
that's 40 lbs on each scale. I am leaning on it 80# to get to brace height. shouldn't I shoot for more, like 80 final draw #?
I am not up enough on your mass formulas. I have the general idea, but not the numbers to make the calcs
thanks again
willie
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ok I got the book out now, and I see the bendy handle number in the 32 inch column reads approx 17.7 for a 50 # bow
23.6 - 17.7 = 5.9
5.9 x 5 = 29.5
29.5 +50 = 79.5
what do I do with the elb factor? 79.5 x .94 = 74.7 call it 75?
hope I am doing the calcs correctly
willie
wait, I for got to subtract the mass I will loose tillering out
if I go with your estimate of 3.5 oz loss, then
20 - 17.7 =2.3, and 2.3 x 5 = 11.5, and 11.5 + 50 = 61.5# ?? plus or minus elb factor??
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As long as your close, it just lets you know if you have enough wood. You have plenty of wood so it shouldn't be an issue if the wood behaves like bow wood.
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I got a chance to put a little time into this bow, and got it on the tillering tree.
I am aiming for 70 lbs. but have not pulled it that hard yet
still takes 80 lbs to deflect the tips 5'' floor tiller
got it to a short-as possible long string, kind of a semi brace at zero with strong string tension, and it takes 45 lbs to pull from zero to 5" draw. seems to have a nice early weight by feel. left it on the tree drawn to what would be 5-6 inches for a half hour and lost 1/2 half of my 3/4" glued in reflex just unstrung. Does this seem like a lit to loose just getting it to a "normal brace height?
How far do I need to get the bow drawn to establish a benchmark of "no set tillering"
thanks
Willie
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Post photos for better advice
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Project 3# per inch of draw and estimate where your bow is now at full draw.
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If I put a long string on a bow I don't pay much attention to how far the limbs are moving. I still just look at where the string is on the measure. If it weighs say 70# at 22" with a long string it will weigh close to that braced with the short sting. It doesn't even matter how much the long string is hanging down within reason.
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Pat B
I am at zero brace with a short string I am pulling about 2.75 to 3 lbs per inch of pull.
first 6 inches took 18#
6 - 10 took 11# more
10 - 14 took 11 # more
doing that caused me to loose an eigth more reflex.
thanks
willie
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Willie, sounds like you are at 40# at 14", it will be about the same if you brace it. What is your goal weight. As for set, start measuring it once you get it braced, some of the early shape just might come out because it wasnt hard set in the first place. Instead of measuring the set, monitor how much draw weight you are loosing by increasing the draw, thats what you are trying to avoid. If it looses draw weight it will also take set. If you start having losses early like where you are now you may want to lower your draw weight expectation, I don't think you have real bow wood you are working with anyway.
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Badger-
39@ 14 is what I have. Hoping for 70#@27". I have lost about 1/2" of the 3/4" glued in reflex I started with. I am having a miserable time trying to get this bow properly braced few inches. Just got back from the hardware store with a turnbuckle. when I put it in the string and braced at two inches, the string slipped, and then I noticed that I have to come up with something better for a temporary nock as I am crushing the soft wood. yesterday I broke a nock and had to wait for some glue to dry on my latest idea.
when get a workable string and a consistent brace I will start pulling and rechecking weights. Assuming tiller is even, how far past 14 would you pull it to get a measure, or to put the question another way, how much poundage loss off the 39@14 benchmark, would you tolerate before retillering for a lower goal. I am not shooting for a real high stressed bow here. Maybe loosing the original reflex plus another inch or so, by the time I get to my design draw length of 27?
thanks for you patience
willie
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If I started loosing more than 1#at 14" I would dial back my target weight all the way to 40#. If I was getting close to full draw and it started loosing a little like maybe 1# @ 24 annother 1# at 25 I would keep creeping up on my goal. I have seen bows loose more than 10# and only take about 2" set, for a 70# bow a 5# loss would be too bad.
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Badger
If I read that right, loosing a pound at shorter draws like 14" indicates a lot more strain and damage than loosing a pound from a benchmark closer to your final draw length like say 25"?
willie
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Thats the way I look at it yes. I don't like to loose any weight early on, maybe 2# but no more than that.
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thank you Badger, I think I understand the monitoring approach better, your input has been top shelf
I have to shorten the bow some and work on the taper some more, add better string nocks.........
will post more with a pic or two after a few days when I get to final tiller, and as time permits that I have time to work on it
willie
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got a chance to work on the bow some more and got it to a low brace of about 2"
the bow got shortened to 70" nock to nock and weight was reduced some.
it presently pulls 43 @ 14"
it pulled 45 @ 14" before I pulled it to 17"
thought I had the bends balanced pretty well before I made the pull, but I have to go back and get the left bending more now.
any ideas how much I should drop my weight goal? the bow is only 1.25 inches wide
thanks for looking
willie
(http://)
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Its already loosing weight but you have a lot more wood you can get working in the center of the bow. I think I would settle for around 50#@ 28. What is the physical weight of the bow?
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Badger
21.5 oz
it took some set mid limb but not in center. the tips droop 1/4' more than before I pulled it
willie
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got the tillering pretty much where I want it and I the bow ended up at 1 1/4 wide by 71 ntn 45@27" with 2" of total set. Larch is kind of pretty but soft. I don't know if the pics show it too well. Kind of cloudy and snowy for good pics. A thanks to Badger for helping me learn a bit more about how to set tillering goals for unknown woods. Any comments on tiller will be appreciated
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I've really enjoyed reading this thread. It's been very helpful nd interesting. I'd like to see how your bow works out over time, too Willie, if you post it.
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When I hit floor tiller I'm probably 20# to 30# over draw weight(just a guess). By the time I get to low brace I'm about 10# over draw weight. As I remove wood and exercise the bow I slowly draw it to my intended draw weight or just below it and check the draw length. From floor tiller I also just use a scraper and rarely a fine rasp when needed. Taking it slow, exercising the wood and watching for any string follow is the way to go. If your bows are taking excessive set you are either using unseasoned wood or over stressing the wood.
That is a great explanation. To the point 100%. :laugh: Most of us resemble that post nothing more to add.
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I don't know the qualities of larch at all. I would assume it to be similar to cedar for my experience with it working arrows. For example if I were working a suspect wood I would probably add about 4" the the draw length I used in a mass calculation..
From what I gather in the wood database, Larch, just like douglas fir, is pretty stiff wood (high modulus of elasticity) but not so flexible (you cannot bend it very far before breaking it). Quite the opposite of yew. Relative to its high stiffness, it is rather good at compression though and average in tension.
You can get an idea at the graph in this post: http://www.primitivearcher.com/smf/index.php/topic,50571.msg692410.html#msg692410
you'll find larch at a relative stiffness of 26, and douglas fir at 27.
Compare this to yew or osage, with a relative stiffness of around 15. This means, for the same limb mass and limb thickness, it takes 1.6 times more force to bend the larch than the yew. But the larch will take set or break at a lower draw length than the yew. It's stiffer, but it cannot take as much strain.
That in mind, I think Larch would be better suited for a long pyramid style flatbow than a longbow. To get the most out of stiff not-so-flexible wood, I'd go for thin and long limbs, being less strained. To gain poundage, make'm wider. Pyramid limbs allow near-circular tiller with even strain along the entire limb.
In principle, for the same bow mass, a larch bow is capable of storing the same amount of energy as a yew bow, but it requires a different design IMO.
Now, with the tillering approach you took, you can make a longbow out of larch. My guess is it will be a bit less deep and a bit wider compared to a yew longbow of the same poundage and length because of the reasons outlined above.
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bow101
when one has a weight goal in mind before starting to tiller the stave, the method described by by PatB seems to be as good as it gets. But what do you do with a stave with unknown quantities? If you are tillering to see "just what I can get out of this wood" , (as DC was asking in a recent thread), I would think that one would have to approach tillering from a different direction.
That in mind, I think Larch would be better suited for a long pyramid style flatbow than a longbow.
joachim-
This bow was en experiment of unknown woods and as a trybow for a future warbow. It gets pulled to 32" and then some. It recovers nicely from just unstrung set and retains about 1" from where the tillering started. It is basically flat for 2/3 of it's overall width, both back and belly. Not really a long bow cross section.