Primitive Archer
Main Discussion Area => Bows => Flight Bows => Topic started by: sleek on January 06, 2015, 01:39:19 am
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(http://i1092.photobucket.com/albums/i411/rocketernally/20150105_233002_zpstfhisznp.jpg) (http://s1092.photobucket.com/user/rocketernally/media/20150105_233002_zpstfhisznp.jpg.html)
As I said, a poor attempt at the E.R.M.B.R. extended riser mid limb bending recurve bow badger built. I deflexed the fades ( I did my best to keep them from bending. Find out soon. And didnt recurve the limb quite as much because I dont have a wide enough stave. Its 1 1/4 wide at its widest. I went narrow out the handle getting wider towards the outter third then brought it back in. The mid and outter third is where the bending is happening with the last 7 inches of tips stiff. The bow is propeller shapped if you can visualize it. Shooting for 45#@28. Probably going to get a broken bow, never tried this before.
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(http://i1092.photobucket.com/albums/i411/rocketernally/20150105_235359_zpsqcg9hbui.jpg) (http://s1092.photobucket.com/user/rocketernally/media/20150105_235359_zpsqcg9hbui.jpg.html)
Crap pic I know but here is the profile.
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(http://i1092.photobucket.com/albums/i411/rocketernally/20150106_002146_zpsfmaryqwb.jpg) (http://s1092.photobucket.com/user/rocketernally/media/20150106_002146_zpsfmaryqwb.jpg.html)
At 26" here, my comfy draw length. Pulling a dead even 40#. Bottom limb wants heat out the fade there.
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Well it shoots. Im getting a small amout of handshock, gonna look into that. I still need that bottom fade addressed, more heat I hope will help. Also, before first brace I traced the outline of the bow on a 2x4. After 10 shots I unbraced and laid it back on the outline. All the set is in the outter limb, 12 inches from the tip. No set in the fade or inner third. Going to go back and reflex the outter limb again to get the profile back and hit it with more heat to harden the wood into shape. First time I didnt use any more heat than needed to bend the curves in. This time im gonna cook it.
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Sleek, have you got an unbraced profile shot?
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(http://i1092.photobucket.com/albums/i411/rocketernally/20150106_092838_zpsk0ndtqvx.jpg) (http://s1092.photobucket.com/user/rocketernally/media/20150106_092838_zpsk0ndtqvx.jpg.html)
I only put in two inches of reflex. It keeps one inch. I think I will try for 5 inches, half of yours, as I am half as wide and probably only half as good as you, and see if it holds together.
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Sleek, if you put two inches and it lost one I would not put anymore. You will just add hysterisis to the bow. If you want to build a bow with 5" reflex design it to take 5". Either more working limb or much wider working limbs.
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What's the length of the bow?
I would give some more reflex in the outer limbs a try plus more working limb. I guess Badger is right about adding hysterisis.
What about sinew- backing?
In my experience osage is a bad candidate for heat-treating, cause it is so dense.
This design is delicious to tiller, very soon you could end up with a low drawweight, cause the long reflexed outer limbs are working as a powerful leverage. It took me some trials and errors to get the desired drawweight.
But done right it is a killer.
Michael
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I cheated. I tillered it out to brace before bending in all the curves. That way I know once the curves are in, exactly where I am at.
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Im sorry, I forgot to say, its 62" ttt.
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How much can hysteresis affect performance? Can it be enough to over come the benefits of added string tension? How do we measure hysteresis?
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Ok, I went back over my recurves with heat. I didnt add any more reflex, but put back what I lost with extra heat this time. My weight went up 4# to 44#@26. I also ploted the fd curve out to 26" of draw. Starting at 9 and going to 26" in pounds its 6, 10, 12, 14, 16.5, 18.5, 21, 23, 25, 27, 29, 30.5, 32, 34, 36.5, 38, 42, 44.
Now.... what do I do with this information? Specifically to calculate stored energy and efficiency?
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Im looking around this and thinking, wow, thats very linear. Probably not that geat a draw curve. I need more pre loading in the early draw. Need to get my string tension up.
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Sleek, to get all your numbers you have to shoot it through a chrono. You never know about hysterisis until you actually shoot it. Your bow is storing slightly less than 40# of energy at 26" which is not too bad for a 26" draw.
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Would the bow benefit from another two inches of draw? Or should I leave it be? You mentioned a sweet spot before and I dont know how you quantify that?
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It might benefit some and then again it might take more set. More set is almost a certainty.
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Guess I will leave it be then. Gadda get my chono out... and a grain scale. Mine broke.
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Anyway this bow is more than a poor attempt.
Give this design another trial!
Michael
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Seems im only storing 86.8% of full draw energy here. I need way more than that to get near to Steve's bow. Perhaps if I drop the draw weight some, and rake advantage of the reduced stress on the wood to add more reflex for higher early draw weight? I may make one more of these bows but not untill I have learned all this one can offer me.
On this bow I have only the middle third working. The limbs are elliptic shaped ( think narrow paddle bow? ) and only bend in the fattest area. The working section on each limb is 15" long on each limb. I have 7" stiff tips, bow limb width is 1.25" at its widest with a long handle fade area 20" long.
Next one I would build, so far, I would only make a wider limb to allow for more reflex and less set. Id keep everything else the same. Should I?
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Sllek, I don't think you have enough wood to do that, you would need about 5" reflex and need to have all the bend right out of the handle. Take advantage of the nice clean lines you have and just thin down the tips, that bow should shoot very well if the wood is dry.
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These designs take a few tries and then some to get somewhat right and dialed in. I've made some,and still feel like I have some room for improvement with them. Soooo....keep on keeping on. Learn from this one,adjust,and try again and again. You put forth a good effort here,and I wouldn't call it a poor attempt.
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What a swizz... I expected a curve... not a string of numbers >:( ;).
So... I've plotted it for you :) (courtesy of Excel and paint)
It's pretty linear, within the limits of measurement error.
Initial draw weight comes up fairly quick rather than being a straight line from zero. E.G the main straight line, if extended crosses the zero draw line at about 6#. In reality there is obviously zero pounds at zero draw, but presumably this is some sort of indication of the stored energy at brace?
Del
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it seems that the deformation concentrates on the areas near handle，which would result in over compression of fiber