Primitive Archer
Main Discussion Area => Bows => Topic started by: gfugal on February 14, 2017, 05:54:11 pm
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So here's some pictures of my latest project. It's a recurved red oak pyramid bow. It's about 64 inches long with an original 3.5 inches reflex due to the recurved tips. You might be able to make out in the last picture that its 2 inches at its widest and slowly tapers from there. I've been trying to get it to brace but it looks like I should have been more patient.
Here's my delema. I've been trying to follow all the instructions on preventing set. I was checking for even bend the whole time. As seen in the first picture, I thought the limb movement was good. If anything it seemed like the top limb (right in picture) was bending more. Turns out it was the strong one when I braced it. I also tried to go slow and not pull more than the intended draw weight. I'm aiming for a 60 lbs bow. It's funny, I would pull up to 60 lbs at shorter limb movement, but once I started getting several inches of movement I dropped the threshold weight to 50 lbs but it didn't seem to matter. I did this because I thought I noticed it possibly getting some set, but I wasn't sure.
I didn't try to brace it until I was at a limb movement further than it would be braced. In the first picture, the limbs are bending about 7.5 inches, which is 1.5 inches further than the target brace height of 6 inches and 3.5 inches further than the low brace height of 4 inches pictured in image 2. That's why I thought it would be okay to put it at low brace because I was afraid the long string tillering was throwing things off (which it seems like it was). However, once I got it to low brace I realized that the limbs were not even, with the top limb (right) being too strong. After I unstrung it I saw that it developed about an inch of set (as seen in image 3).
I'm frustrated and wish I would have got the limbs bending further safely before I tried bracing it but didn't like doing that with the long string. Why do you think I got set? Maybe I had it too strong? but then again I had it pulling less than 50 lbs which is even less than the 60 lb target weight. maybe I should have had further limb movement before bracing? but I was afraid the long string tillering was throwing me off. I also wanted to move away from the long string as fast as possible because I was worried it would overrepresent the true strength of the bow, and I was worried off having too week of a bow? Was my design wrong? I thought 2 inches wide would be more than enough for a 60 lb bow. Maybe it is just a bad batch of wood? I'm not sure. What should I do from here on out?
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The recurves are straining the limbs more than a straight bow.
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Yes that's right.The reason your right limb took that set is because it is bending too closely to the fades.Your left limb is sharing the load better over all.I imagine you thickness tapered the limbs from the fades outward the way they are correct?Leaving them parallel width to at least midlimb would of helped to carry the inner bending load a little better.Recurves are beautiful profiled looking bows but at a cost.More strain and a little more fickle to tiller also.Not as forgiving so to say as a straight limbed bow with a longer working limb.
You've got a bow there yet though.Just a little lighter weight.Everything else you did in my eyes you did correct from long string to short string.Get the right limb bending more on the outer third.That will bring the that limb to match the profile of the left at brace.Getting them to look identical at brace.Then tiller her out removing wood evenly from both limbs excercizing it.
Actually I can see in the pic the right limb is thicker on outer third below your recurve.
BTW...Good pic you took also.You did the right thing checking your bow for set before it got out of hand BTW.It's what everbody should do.
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if you are leaving the bow pulled on the tree, that can cause some set,,
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You're always going to get some set. The question is only how much.
Your bow is relatively short, not very wide, reflexes which adds stress, and made from a wood which is not the best (although red as obviusoy can make a nice bow).
I think the amount of set your seeing is very reasonable and normal. You should definately aim for minimal set, but don't get worked up over it. With those dimensions and draw weight you're shootings for I wdon't uldnt expect to be left with much if any reflex in the end, but that's ok.
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True the recurves shortened your working limb. A good rule of thumb is to have the working limb the same length as your draw length and to only start pushng this onceyou have a few more bows under your belt.
As your limb profile is pyramidal your limbs aren't bending enough in the inner third. do you see how the set is all in the mid limbs? On a pyramid the bend should be the same on every part of the limb (arc of a circle tiller). With right off the fades being a little stiffer but certainly the inner limbs should be bending more than you have them.
Recurves generally do a bit better with a parallel width for 3/4 of the limb then a taper into the tips. The ptramid design is best for a straight limbed bow.
Red oak is one of the woods with a 'mismatch' to its properties. Its resistance to tension is more than its resistance to compression. A process called trapping is very useful on red oak and other tension strong,compression weak woods as it evens out the stresses in the limbs to a point where the wood is more able to take those stresses without being overstrained. If you went to a bandsaw and cut your limbs in half I bet that the back would go back to straight and the belly would actually go into more set. I've done this experiment a few times to see what is actually going on when a bow takes a lot of set and it sure is an eye opener!
So your bow is a bit too short, needs the tiller adjusting and it would be a great idea to heat treat the belly and trap the back. watch any set like a hawk and note that it should be even along the whole limb (bar the fades!), if it isn't the places with no set are stiff and the areas with more set are weak.
Good luck.
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I don't have any tillering advice per say but it took me about 8 bows ,I'm a slow learner to figure out that by far the most important process in the tillering phase is the floor tiller in other words the bow should be bending even & hinge free by the time you get to brace and you eliminate set causing & weight robbing hinges it's a matter of not stressing the wood more then it has to just baby steps a long the way & also not leaving a bow pulled beyond brace more then a few seconds, no expert here just passing along lessons learned, also you must be a single guy with running a band saw in the house....lol
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Don't get frustrated and never quit. Learn from your mistakes and keep going.
Learn to love the journey.
It took me 3 years and 14 tries to get a hunting weight shooter.
Jawge
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I could see why the length would cause set once I get it bending far, but it's still way far from that. Suppose I was aiming for a 25 inch draw, a 64 inch bow NTN would be 14 inches longer than twice the draw length rule of thumb. That's enough to account for 8 inches of non-working handle and fades and 3 inches of non-working recurves. But still, I haven't gotten close to even a 25 inch bend. So I don't think I can contribute the set this early on being from too short of limbs.
I rarely see bows wider than 2 inches posted on this site so I was assuming that was more than enough width, but I could have been wrong. maybe it was the pyramid design that was wrong for the recurves, like was mentioned. But I'm thinking it's probably at too high of a weight right now anyway, I should bring it down at least here in the beginning. I've read that you shouldn't pull it past the target weight, but I'm starting to think that I should take that further and not even pull it past some percentage, like 70% or 80%, of the target weight until after I get it braced. Do you think that's a good Idea? I'm thinking of adjusting my target weight to be 50 lbs instead of 60 lbs.
It's also good to know that red oak is somewhat lacking in its compression capabilities. That makes me feel better, cause I don't have to take all the blame on my design and tillering abilities. What are common woods that have good compression?
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Even besides the tiller not being perfect for the profile, that length with those recurves in red oak should definitely be more than 2" wide unless it's an exceptional piece of red oak. The recurves each are essentially reducing your working limb length by 5-6" each and the handle adding another 8" or so reduces your total working limb length to 44-46". And that's if your length is 64" between the nocks. Even less if the total length is 64".
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I could see why the length would cause set once I get it bending far, but it's still way far from that. Suppose I was aiming for a 25 inch draw, a 64 inch bow NTN would be 14 inches longer than twice the draw length rule of thumb. That's enough to account for 8 inches of non-working handle and fades and 3 inches of non-working recurves. But still, I haven't gotten close to even a 25 inch bend. So I don't think I can contribute the set this early on being from too short of limbs.
I rarely see bows wider than 2 inches posted on this site so I was assuming that was more than enough width, but I could have been wrong. maybe it was the pyramid design that was wrong for the recurves, like was mentioned. But I'm thinking it's probably at too high of a weight right now anyway, I should bring it down at least here in the beginning. I've read that you shouldn't pull it past the target weight, but I'm starting to think that I should take that further and not even pull it past some percentage, like 70% or 80%, of the target weight until after I get it braced. Do you think that's a good Idea? I'm thinking of adjusting my target weight to be 50 lbs instead of 60 lbs.
It's also good to know that red oak is somewhat lacking in its compression capabilities. That makes me feel better, cause I don't have to take all the blame on my design and tillering abilities. What are common woods that have good compression?
You're not accounting for a recurve being the equivalent of a bow braced about three inches higher and drawn three inches farther than if it was straight.
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wow thats a nice formula,, the recurves are putting a extra bit of strain into he formula,,
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So, I still think it's a good attempt, and don't let it get you down! I love what you are doing, and I'm excited for you to keep getting this stuff spot on. And, REMEMBER, everybody messes up bows. Don't take this as critical, just constructive criticism. BUT, I do see several things that MIGHT have done this to you..... Overall you were simply asking too much of the wood, but here is why.......
First it's oak. Red oak varies a lot in density and quality, and while it is FINE wood, it isn't excellent and gets recommended for availability more than anything. If I was making an oak pyramid bow I expected to shoot 60 LBs at 28", I'd have started with 3" wide, not 2". At 60 lbs, it needed to be longer, or wider, or less strained.
Second, you CANNOT simply slap BIG recurves on a pyramid style bow and expect it to work well. The pyramid design (consistent triangular side taper and essentially even thickness, creating circular tiller) is, by definition, a straight limb bow. Recurves alter the entire set up by changing where, how, and when leverage is applied during the draw. If you do this again with another board, do the thickness of the limbs to a good starting point, but leave the sides parallel out to, say 2/3 the limb length before you taper to points. Then, you can tiller from the sides a bit.
Third, That bow is pretty short at 65" (not for a recurve, but for oak), and since the board was pretty narrow that cost you. Look at your third pic and visually divide each limb into four sections according to length, from the handle outward (0-25% , 25-50%, 50-75%, and 75-100%). See how you have very little set down by the fades, but more in the third section (50-75%), just below the recurves? You needed more width there and in the 25-50% section.
Fourth, those recurves are HUGE. I actually want to congratulate you on getting them in there Now, I make some huge recurves, and I love them, but if I go 25% of limb length (like you did here), and over 45 deg angle, I usually deflex the handle or the limbs at the handle. This is mostly to benefit stability, but obviously helps reduce limb strain. I have flipped the tips an inch or two on many a pyramid bow or flatbow, but that was just too much draw weight, and too much curve.
Finally, See on your first pic how the lower handle is fatter than the upper handle? That's tipping your bow on the cradle of your tillering tree, which is why you though the upper limb was weaker. I eventually learned to use all kinds of shims, teeter-totters, and clamps to avoid that. You are tillering toward the bow's balance point in your hand, not just the handle, or the middle...
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Even besides the tiller not being perfect for the profile, that length with those recurves in red oak should definitely be more than 2" wide unless it's an exceptional piece of red oak. The recurves each are essentially reducing your working limb length by 5-6" each and the handle adding another 8" or so reduces your total working limb length to 44-46". And that's if your length is 64" between the nocks. Even less if the total length is 64".
You're not accounting for a recurve being the equivalent of a bow braced about three inches higher and drawn three inches farther than if it was straight.
I didn't know to account for the recurves when determining the length, that's good to know. Thanks. Assuming a worse case scenario of only 44 inches of working limb I should still be able to make a 22-inch draw bow without stressing this design, right? I haven't gotten the limbs moving anywhere close to that far yet, so theoretically I shouldn't have set due to flawed design yet. But I do have set already, which indicates to me this set isn't due to the fact the limbs are shorter, this early set is due to something else. Either I'm expecting too much of the wood because the wood isn't ideal and can't take it, or I'm doing something wrong with my tillering. I think it's a combination of both?
I can't change the design at this point so I'll take yalls suggestions to my next bow. What do I have to do now with this bow to prevent further set? If I'm expecting too much from the wood how far down should I bring the target draw weight. Should I also try avoiding even going over 70-80% the target draw weight until braced with good tiller. What should I do for the tiller, other than taking wood off the right limb to equal out the two's strength? Does uneven strength cause set, or is it more to do where most of the bending is taking place on the limb? I'm still confused, I have Beadman saying take wood off the outer third of the limb and Mikekeswitch saying to take wood off the inner third. Also, what did you mean about trapping the back Mikekeswitch? You mentioned it but never said what it was exactly.
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I've never made a bow that didn't take set, not one. For that matter, nobody ever has. That being said, the advice you received on this particular bow is pretty darn good.
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Spring Buck thanks for that, I didn't see your post until after I posted my response. you've answered some of my questions raised in my reply. Again I just want to say thanks for all the advice. Sorry If I'm coming off hard headed. I'm just trying to break everything down and clarify it for myself.
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ok you are getting alot of info,,
even if the bow does take some set,, guess what,, it can still shoot great,,
reduce your your goal target weight and draw,, and you should be able to get a nice shooting bow,,
it may not have the great cast your were execting , but the arrow will fly nicely,,
moisture content and variation in quality of the wood are proablly an issue as well,,,
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"I rarely see bows wider than 2 inches posted on this site so I was assuming that was more than enough width"
Two inches would be plenty with osage, or maybe black locust, or yew, or plum, but even then, I'd carry the full width farther up the limb.
"Maybe it was the pyramid design that was wrong for the recurves. But I'm thinking it's probably at too high of a weight right now anyway."
These are the biggest factors.
I've read that you shouldn't pull it past the target weight, but I'm starting to think that I should take that further and not even pull it past some percentage, like 70% or 80%, of the target weight until after I get it braced. Do you think that's a good Idea?"
Sure, why not? But, I would have, I suppose ANY of US would have had the same problem you did. It took set early not because you failed during tillering, but just because the design/wood/strain/draw weight combo wasn't a good fit.
"I'm thinking of adjusting my target weight to be 50 lbs instead of 60 lbs."
If you had started at 50 lbs, you'd have less set. The pyramid taper would still be a problem, but not as big a problem.
Seriously, don't get discouraged. I did this stuff, and so did many of us here. Thinking and trying is awesome.
And remember, I have stuff in my garage I'll happily give you whether you succeed of fail with it. At the rate I'm (not) making bows, you better come get it before the bugs do!
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You aren't coming off hard headed. I personally can't remember things until they make sense. I have to understand it pretty well, then it all sticks forever. A bunch of loose rules, or straight instructions means nothing to me.
I'm like a big four year old, always asking "Why?"
And PearlDrums and Brad are right. Set is neither unexpected, nor the end of the world.
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Well first you are pulling it to far with the tiller that far off, even out the tiller before you go any further, i usually don't put the recurves in till I'm at 20" draw and tiller is spot on or darn close, that way it's pretty close after you bend the hooks in with no suprises and you can go to full brace and adjust any tiller issues that came up with the recurving process. I wouldn't pull that farther than 12" till i got the tiller squared away
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Probably been mentioned already but also consider humidity. Red oak can be extremely variable in terms of quality for bow wood. I've picked up some boards with great grain straightness but narrow rings and even at long lengths and light draw weight they took some set.
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Should I also try avoiding even going over 70-80% the target draw weight until braced with good tiller.
Perhaps even a bit less?
On a short as possible longstring, the most recent bow I tillered had the tips move back half way to where they would be at full draw, with approx half the design draw weight. This was done as a bit of an experiment and before first bracing. Good visualization skills are neccessary to see the finished bend in a bow at brace height, as I found that there was very little wood left to remove to finish out. This was on a straight bow BTW. As other have noted, your recurve design means that your tips have to come back further to get to a normal brace height. Someone with recurve experience may wish to comment on the viability of tillering at a very low brace with your design. Of course, the lower the brace, the harder it is (for me, anyway) to predict the finished curve shape.
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Here's a picture of it braced. When trying to fix it, it looks like I was going too fast and started to develop a hinge in the middle of the top limb (now left side). To fix it, do I just rasp on either side of it? Or should I just focus on the side towards the fades? I'm thinking it could bend more in the inner limb
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OK.Looking a bit better.I see the bow is reversed.According to where your arrow shelf was and is now.In the first pic it had a negative tiller.Now it has a positive tiller but not near to the same degree.
Try this if you don't trust your eyes.You will in time but till then make a pencil mark on the side of your bow limb at the fade on each side of each limb.Measure out every 6" make a mark on each side of each limb.Make at least 3 marks this way all along the working limb to the base of your recurves.Now at brace take your tape measure and measure from center of belly to your string.Compare one limb to the other with those measurements.
Those three marks on your top limb should measure slightly longer than your bottom limb at each mark for an over all positive tiller.
Not knowing what you want for a positive tiller figuring you have equal limb lengths I usually go for about a 1/8" positive tiller that way over all.Others may like different ratios of positive tiller.That's just me.
Reading through other comments I agree that there are different ways of avoiding excess unneeded stress put on a bow to brace and after to tillering.To avoid that and to explain that all would be better done in a shop I'm afraid.It'll come with experience too.
Set happens as George says and many others.Especially on recurves.Noone gets around that.Your pretty darn close.
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So positive tiller is when the top limb is weaker, and negative tiller is when the bottom limb is weaker? And we want a little bit of positive tiller?
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Do you have much more to take off? How far have you drawn it and what is the weight? If you still have quite a way to go then put a bunch of X's on the belly of that hinge and don't scrape there for a while.
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Do you have much more to take off? How far have you drawn it and what is the weight? If you still have quite a way to go then put a bunch of X's on the belly of that hinge and don't scrape there for a while.
I haven't drawn it that far yet. It's 10 lbs at 11 inches which is weaker than I would like. I'm figuring if I drew it to full draw now it would be close to 50 lbs but I figure that little hinge will start to manifest itself at a further draw so I'm going to have to take some off. I'm hoping to have the bow be 45 lbs, but it most likely will be 40 lbs.
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I'll bet you can do it. Just don't scrape on the hinge until you catch up to it(or however you would say that)
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Yes a slight positive tiller is desired by most.Just the way it's done.Having it be a lower poundage bow in the end will reduce set to a degree.How much I can't say.The wood will tell you.When you get the tiller to be good and balanced then go ahead and pull closer to your target weight at whatever that draw length is.Healthy recurves usually always have higher string tension and higher draw weight in the beginning of the draw more so than straight limbed bows.An educated quess here thinks you are'nt too far off saying you have around a 50# bow there yet.
How much set will be revealed at that time then too.It is quite a bit of strain on the length of limbs you have there with it being red oak.
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That's a good way to say it, DC.
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I highly recommend you read the Bowyer's Bible Vol 1, particularly the Design chapter by Tim Baker.
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I just wanted to post an update. Here's the bow drawn to 22". I got the limbs near even at brace, but couldn't remove completely the hinge in the top limb (pictured left). However, it no longer looks at all hingy, just like it bends a little too much there. I don't want to take off anymore wood trying to fix it unless I have to. what do you guys think? I'm already underweight. It's 27 lbs at 22". My target weight was 50 lbs at 32", but I don't think I'm going to go all the way out to 32" anymore, probably just to 30". I'm hoping to break 40 lbs. It hasn't gained much more set, but unfortunately a little bit (about a centimeter). It's set is 1.5" for the top limb and 1.2" for the bottom. My current plan is to heat treat the belly since I've got most of my scrapping done with. From there I'll just keep pulling it one inch at a time, checking the bend, until I get to draw weight. How long should I wait before bending after heat treatment?
I highly recommend you read the Bowyer's Bible Vol 1, particularly the Design chapter by Tim Baker.
I have read it several times, but am currently re-reading it now. It never hurts to re-read it, especially after you've experienced trying to make a couple bows. :)
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A 64" bow with the recurves you have on there wanting to pull it to 30" and it being red oak I think you've done pretty good so far really.Your asking a lot from red oak I'd say.Osage would handle that a lot better but I suppose if you had some it would be up here now.The osage I think would of kept your weight up higher too.Going down in weight on the red oak is helping it I think.Heat treating it might gain some poundage for you but then I'd be leary of the back then.Hickory can handle that but I don't know about red oak.Rawhide over it I think would be good security myself.Even linen string backing would make it more durable too.
I did a linen string backing on a KCT bow once.Made it almost unbreakable.It gained almost 8 pounds in draw weight then too after the linen string backing was glued on.It was a 64" bow too.Twenty eight 12 ply strands length wise on the back.That meant for each 4 strands I gained 1 pound in poundage.
All in all your doing pretty darn good I'd say.The bow looks nice.After heat treating I have a 10 day rule.That's just me.