Primitive Archer
Main Discussion Area => Bows => Topic started by: dragonman on January 20, 2016, 10:27:07 am
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I find with many of my bows that I shoot a lot, the distance between the bottom limb fade out and the string very very gradually increases, when it gets to about 1/8"difference in tiller I usually reverse the bow , so that the bottom limb becomes the top and this solves the problem, but then the same thing gradually happens, over maybe a few thousand shots....in some cases I keep doing this.
Does anyone else have this same experience? Do you think this is down to shooting style? stressing the lower limb more with an unbalanced draw?,Is it poor tillering? or could there be other reasons....Some bows dont do this ,but a lot do!!
I was once in a club where a few guys had ELB's and I noticed this had hapenned to their yew bows, one case was severe....I told him he should reverse his bow and it may fix the problem, but he didnt believe me and left it!!!...so I know its not just me
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I have seen this quite a bit on self bows, not uncommon. It just means that the bottom limb is getting stressed a bit too much and taking set. Your hold is likely putting more pressure on the bottom or your MC levels may be varying some. Wood is not as forgiving as glass. I try not to build mine too close to the edge anymore for this reason.
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Occasionally but not that often
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I'm with Marc. When it does happen I know why right off the bat.
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so why would a bow that had an exact tiller for months start to develop an inbalance??
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so why would a bow that had an exact tiller for months start to develop an inbalance??
If a bow is marginal, too close to the edge of being stressed one slight overdraw can throw the tiller off. I like to tiller mine for a couple of inches more draw than I actually shoot at to keep them stable. I used to store my bows in a big cardboard drum. I didn't even think about the lower limbs gaining and holding more moisture than the top limbs. First time when they were draw comming out of the barrel some of them took set in the lower limb.
I never did like that phrase about a good selfbow being 90% broke. The stage before being broke is when they start taking set. I like to stay inside what we call the elastic range and then your bow will stay stable for years.
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that makes complete sense Badger, thanks. I store my bows horizontal for that very reason , so cant be that...and I do usually like to push design limits so that explains it.....I am going to follow your advice on this.
Dave
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I dont understand moisture gathering at the lower limb? Does dead wood not still draw water up? If not, then which ever end is down gets excess moisture. So the best way is backside down belly up?
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Water runs downhill sleek.
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I agree with Badger, and the closer to the edge the bow is,, the more likely moisture content or an overdraw could effect the tiller in a negative way,, when I shot alot of tournaments,, if I shot two days in the rain with the bow strung all day the tiller might shift,,, lots of moisture out there,, I seem to have this happen more with sinew bows and I will just shoot the other limb up if needed,,I think the sinew bow is more sensitive to the moisture,, just more sensitive in general,,
I have thought of making the bottom limb longer since it is under more strain,, but have not done that yet,, and I usually start out with a little more positive tiller than needed in case it does shift a bit,, sorry to ramble,,
but I think the bows we see from the past with a shorter bottom limb did not start that way,, but was just a tiller adjustment later in the bows life :)
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I have never noticed a problem from storing staves vertically, but it sounds very possible that water would sink into the bottom limb..so I turn them around occasionally...
as for making the bottom limb shorter or longer, I have heard theories that make sense for doing both...I think just make it a bit stronger, if its necessary...I.do try to leave the bottom limb slightly stronger, but they always tend to end up about equal in the end for some reason!!!
I think Badger hit the nail on the head. If this happens at some point later on in a bows life the bottom limb must have been very near the limits of its tolerance, and some small change was enough to overstress it. otherwise it wouldnt move
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I don't think storing them verticaly was the problem, I had a bucket full of bows with no air circulation. The humidity in the barrel was much higher than it was in the air. The top limbs got plenty of air circulation.
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Moisture inside the bow will allow gravity to yank it down, however minute it is. When I'm drying a blank, like I am now, I flip it end for end every couple days. Maybe that's being anal, but hey. I want to build the best bow I can so I pay attention to everything and hope in the end it adds up to something.
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Dragoman,,I think the trend over the years has been to make the bows more stressed,, pushing the limits of the wood,, and there is a trade off for that,,if the bow is going to be shot very little it will not show the signs of stress very quickly,, one of the best lessons I learned was from a guy I made bows for,, Mike Prince,, he would shoot several hundred arrows nearly every day out of my bow,,,,, if anything was going to give it gave,, gradually I learned that slightly overbuilt was the only bow that would hold up,, and that was a delicate balance, because the bow had to have good cast for him to compete on the level he desired,,lucky his draw was 29 inches so the power stroke made for a nice cast if I did my part in making the bow hold up,, :) if the bow held up to several thousand shots,, then it was usually stable from that point on,, when I tried to put the bow to the edge,, something usually gave :)
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Thats the same way I feel Brad, I gave up on the super skinny bows or super stressed designs.
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I never got into them :) Just boring old flat bows or flat bows with static tips. Yaaaaawn....
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I never got into them :) Just boring old flat bows or flat bows with static tips. Yaaaaawn....
Those are the best kind!
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I agree Steve! I think the #1 reason for that is my usage. I hunt, that's about it. I want stable, rigid, heavy duty, aint gonna break bows when I hunt.
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Dragonman, Chris, Steve & Brad ...Great conversation and information!..Thanks
DBar
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Very interesting stuff, drying staves and moisture content is a constant battle for me in the PNW.
I'm a positive tiller guy, they look and feel just right to me.
A couple of my better bows are still very balanced after many many arrows, but some of my earlier symmetrical limb bows show weaker bottom limbs.
Whenever I build a bow for someone else it's always a little overbuilt, for many reasons.
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Sorta related. An awful lot of the bows posted on here look like the bottom limb is weaker. Is that a camera/picture problem rather than a weak limb.
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This has me wondering what their tiller profiles were like originally and whether they were symmetrical or asymmetrical. I know many folks like 1/8" to 1/4" positive tiller as a general rule, but I tiller mine to balance relative to the archer's holds with no thought toward such predetermined measurements and I have never flipped a bow due to shifting tiller. Some of my bows end up with an even or negative tiller, even when I leave the bottom limb a wee bit stronger at full draw, relative to the holds on bow and string. I can't remember the last time I had a bow end up with a 1/4" positive tiller... unless it was due to a hump or other natural obvious disparity between the limbs. Naturally, this leads me to wonder whether many bows are tillered a bit too strong in the lower limb... or I'm making mine wrong ;^)
I'm just gonna think out loud here for a minute... and then let me know if you think this is a possibility, or I'm all wet.... Lets say we tiller a bow purposely so that the bottom limb is too strong, relative to our grips on bow and string. This would make the bow want to tip in the hand, with the bottom limb coming toward us without flexing as much as the top. Could this cause us to inadvertently push into the lower limb harder to resist its stronger force against the bow hand? And if so, and enough, could this change/weaken the lower limb just a tad after much repetition, which would show as a change in braced profile, and cause us to want to flip it? ...and start the process over? In other words, could making the bottom limb stronger than the top(relative at full draw) make it more prone to tiller shift, rather than less?
When these bows shift, do they shoot any different? Better? Worse? Anybody ever just keep shooting them like that and see what happens?
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I have to admit that I think a lot of these tiller changes come from something that Pearl Drums brought up a years or so ago. I've been thinking about it ever since--maybe a bow is not really a bow until it has been shot 1000 times. The context was different in the thread at that time but the principle may be the same, whether we are talking about tiller, broken bows, or what distinguishes a true bowyer--the bow that looks great after a 1000 shots really determines all of this. I personally have adopted this approach as a barometer in determining success.
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Its a bow once its shot an arrow until it breaks. Is it a bow i would trust? Too many factors.
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yes I think a bow will settle in after 1000 shots or so,,and has not revealed its true self until then,, I agree,,
Dances with Squirrels , I will try to answer the questions I have experience with,,
Yes I have kept shooting the bow after it shifted and it depends on the bow, and most of all the length of the bow( some bows won't shoot if you put the bottom limb up, the string is on the wrong side)
from my experience ,, the way a longer bow shoots is not as sensitive to tiller shift,, the bottom limb can be weaker and with nocking the arrow in the right place or adjusting the hold on the bow,, it will shoot fine,, good arrow flight etc,,,not a problem,,
some bows may require a slight tiller adjustment to get the arrow to fly as smooth as you like,,( some shooters don't shoot well enough to tell when the tiller shifts or not,,they may just be starting or have a poor release etc and have never seen an arrow fly correctly)
for me,,the shorter the bow,, the more critical the positive tiller seems to effect the way the bow shoots,, probably string angle etc and some things I don't understand, but I can feel it in the way the bow shoots and arrow flys,,,, not as well as a short bow with positive tiller for the way I grip and shoot a bow,,
I don't think having a bow with positive tiller causes the bow to shift tiller,, I think the way we hold the bow and grip the string will put more pressure on the bottom limb,, and the bow has to be designed to handle that,, if that is longer or wider or shorter draw ,,,
if the bow is being shot in high moisture conditions or stored as Badger explained,,,that could effect a tiller change as well,,
as far as your bows go,, a self bow may not reflect a positive tiller at brace,, but at full draw the top limb is weaker or working more than the bottom limb, and so shoots as if it has a positive tiller,,even though the braced profile does not show it,,
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I make my limbs the same length but my arrow rest is about center. I tiller so the arrow pulls straight back. This will usually give me about 1/8" positive tiller but not always. I don't mind going up or down a little with the arrow nock to tune the bow if I have to.
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I usually tiller mine about 1/8 to 3/16 pos. If the wood is well seasoned and dry they usually don't change much if any, one thing I have seen a lot is folks braceing the bow with the step through or push pull and not pay attention, they put a lot of pressure on the lower limb if not careful. I use the push pull but a stringer is the safest bet. I do tent to over build so that may be why I hardly ever have one chance after I am finished. Brad I got the pleasure of re doing one of your bows you built for Mike Prince, it had set for a long while, he got older and weaker ;) and the bow probable picked up a little weight over the years, I took about 10lbs off of it and retillered. it was a fine bow to start , just to heavy for him. :)
Pappy
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thanks for the input, I never did properly understand positive tiller. I tried making a few bows with a shorter bottom limb, figuring that shorter meant stiffer, but it didnt feel right, and bought up more questions than answers, that just seem to over complicate the process. Now when tillering I just put the strongest limb on the bottom when I start shooting the bow in and go from there..
I see a lot of people mentioning gripping the bow, but my understanding is that to prevent torque and pulling the string out of alignment to the left or right , which will disturb arrow flight , the idea is to not grip the bow, or grip it the absolute minimum!! This way neither limb is being forced to bend more as a result of gripping...it will only bend more or less because of limb strength or knocking point position.
Isnt extra force on the bottom limb down to leverage principles? If the knocking point is above centre then the portion of string below the nocking point is longer than that above. Therefore the string is acting like a lever on the bow tips...and as in a lever, the longer the lever the more force it exerts? Untill string angle reaches 90 degrees.
Badger, interesting you say that you make your arrow rest position central!...with a stiff handle bow , doesnt this mean you will need an extra long handle section to acheive this?
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I make most bow with same length limbs and tiller stiffer bottom limb/1/8 to 3/16 for that reason. My arrow is something above center, I never know for sure until I shoot it, I move the arrow up and down a bit until I get the feel and arrow flight I want and then mark it and that is where my arrow sets. I usually put a shelf but never do that until I have shot the bow and am satisfied with how it feels. ;)
Pappy
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I agree that having the lower limb stronger is a good solution. Besides hand grip position another factor in changing tiller over time is that the point of contact and length of contact with the string is different when being pulled by three fingers as opposed to 1/8" metal hook on the tillering tree. This is why some bowyers will test a bow an inch or so further than the final draw length.
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I wonder how much affect temperately setting the bow down after you unstring it plays a part. We all do it, after shooting, we set it against a tree vertically for a bit Then come back for it and store it horizontal. But when its leaning against the tree unstrung, its putting more weight on the lower limb and not allow it to gradually come back straight again, however slight it might be. I wonder if over time, that can "soften" the lower limb.
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I doubt that's it. I use a metal hook and the tiller doesn't change.
Speaking of hook placement though, I'll bet that a cause of shifting tiller in some instances is how some folks tiller their bows by pulling them differently on the tree than they do by hand. For instance, pulling at the center of the handle on the tree, then shooting them with the string hand fulcrum 1 1/2" or so higher. Shifting tiller as a result may just be the bow adapting its new training regimen.
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Guess ill add my 2 cents...
I think using seasoned wood helps a lot in this regard..it may not prevent it every time,but i do think it greatly reduces the chances of it happening as long as the bow has been properly tillered and cared for...theres more shrinkage of wood cells over time even if it has been quick dried soon after being off the stump...ive had it happen twice to me out of all the bows ive built...both were hickory properly tillered,and properly cared for, and stored in a strict monitored setting,but both were under a year old off the stump...ive never ever had any problems with seasoned osage...and i believe the ole timers touted only using seasoned stock because of this issue (or one of the reasons why)
so my answer and solution is to use good seasoned osage!!!! >:D osage will always usually hold what ever tiller shape ya give it even if its a sh!++y tiller job...
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Yes, indeed, on the importance of using seasoned wood.
In my early days when I was bitten by the bow building bug, I would invariably run out of seasoned wood. So I would rush a bow and end up with lot of set.
Then I got a moisture meter and started using it and noted that my bows took much less set.
Then, I'd take a bow off the rope and pulley after tillering from center and find the lower limb taking more set.
Then, I discovered digital photography. Nothing approximates how I pull a bow so I have a family member photograph the bow at full draw to check tiller. I like the lower limb stiffer even or stiffer by 1/4" at full draw.
I don't care too much how it looks at brace. Full draw is important.
One of these days, I'll photograph a bow at full draw after shooting it for a few years.
Jawge
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Interesting worthwhile subject dragonman.Every future or even present bowmaker could benefit from reading this or someone liking the use of primitive type bows.Only those who shoot a lot can see this.Seems like until someone makes or shoots a bow with a lot of refllex the use of a stringer is'nt used.Otherwise the usually push pull method.I never did like the step through method.Maybe I don't do it right.I know I've seen bows strung up not with the exact tiller I put on them then pump on them a few times and they correct themselves.Which still leads me to think bracing a bow evenly is a wise thing to do.The storing vertically or horizontally is up for debate yet.A stable enviornment is needed.After shooting I always try to lay the bow down horizontally just because of the thought of letting the limbs come back unobstructed.I do tiller mine always an inch past my draw just for safety reasons.All in all I don't see the widening of the lower fade over time happen much with my bows as of yet.I'll have to keep a shooting but know a lot of my bows do have thousands of shots through them.1/8" positive tiller is the max for me and my way of shooting,gripping,etc. with the shelve approximately 1.5" above center of bow with even length limbs.
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Ohh forgot to mention the positive tiller I put on a bow is evenly the whole length of the limb too.Seen people just check by the fade when braced and that's it.
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I'm not so sure about the water and gravity part of things. Remember that the water defied gravity in the first place through passive capillary action. Trees don't have water pumps. But below ~30% moisture content, there is no loose water in the cells anyways, it is all bound to the cell walls. AND the cells are clogged with extractives in the heartwood, and the vessels/pores in many hardwoods (including osage).
I've read that the moisture content in the air can differ near the floor/ceiling. That seems more likely if different MC is involved. But I'm not a moisturologist.
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I've heard of guys sliding the larger string loop up the bottom limb instead of the top, stringing the bow with the bottom limb toward the sky, presumably, to avoid making the bottom limb weaker from stringing with the push/pull method. But I'm not sure I'd buy that as a cause of shifting tiller... since we're only straining the bow a wee bit to get it braced, and after a tug or two, it goes right back where it should be.
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Would a low reverse brace help with this? Like a second nock cut into the upper limb to slide the string doen and catch, then pop the bow into reverse brace?
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I'm not so sure about the water and gravity part of things. Remember that the water defied gravity in the first place through passive capillary action. Trees don't have water pumps. But below ~30% moisture content, there is no loose water in the cells anyways, it is all bound to the cell walls. AND the cells are clogged with extractives in the heartwood, and the vessels/pores in many hardwoods (including osage).
I've read that the moisture content in the air can differ near the floor/ceiling. That seems more likely if different MC is involved. But I'm not a moisturologist.
If you have maybe 75 bows stuffed into a drum, you just don't have as much air circulation as you would with the bows sticking out of the drum. I don't see much of a mystery here. Some of the staves were still drying. The moisture level will be higher in the lower potions of the drum.
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The top of the drum is open?
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The top of the drum is open?
Yes, so the bottom half is in a cardboard or plastic drum and the top half is in open air.
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Of course the bottom MC will be higher, and I don't think because of gravity.
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Water vapor rises, it doesn't sink to ground level. So the humidity in the bottom of the barrel would be lower in the surrounding air.
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Pat, when you have air moving across wood it dries faster. If you have a bucket full of bows there is not much air movement. I am well past the theory stage on this. I took them out of the bucket and problem was solved once they acclimated.
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I'm just clarifying what water vapor does. Tim Baker seemed to want to give us the impression that there was low lying clouds in our homes. ;)
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[/quote I never did like that phrase about a good selfbow being 90% broke.
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Sooooooo, 89% broke, then? ;-)
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[/quote I never did like that phrase about a good selfbow being 90% broke.
Sooooooo, 89% broke, then? ;-)
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I would hope less than 80%
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I have never noticed a problem from storing staves vertically, but it sounds very possible that water would sink into the bottom limb..so I turn them around occasionally...
Vertical storage doesnt relate to water sinking in the limb, the capillary action in wood vessels is much stronger than gravity.
The point about bottom limbs having higher MC is IMHO caused by temperature being lower close to the ground in heated rooms (heat goes up) and moisture levels being higher (more damp) in the colder micro-environment the bottom limb experiences relative to the upper limb.
Joachim
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If you store it vertically and in a cardboard container there is goons to be more moisture in the bottom because as moisture evaporates off the wood it cools and sinks. Drying lumber even outside where the moisture is going to be more evenly diffused into the air we have to keep the lumber piles 4-5" off the ground and even then the bottom packs will have higher MC than the ones up top. That is properly stickered air drying lumber too...
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https://en.wikipedia.org/wiki/Water_vapor
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Right, it's not that the water is sinking in the wood it is that the humidity is higher in the box which slows the evaporation from the limb where the one exposed to the currents however so slight will lose moisture more readily. I am not a moistureologist but I do dry wood for a living and don't trust everything you might google or or intuitively suppose haha. I googled how to make a bow a few months ago and what I "learned" was lot different from what I've learned here lol
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I'm not disputing that lower limbs or boards might be damper, I'm disputing how they become that way. We can't make up stuff that is disputed by Science. ;)
My intuition says it's because the ground has more moisture, not the air and the wood wicks that up.
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Wooden floors require moisture barriers for a reason. Fog settles.... Dew settles... Earth is damp. Perhaps it many reasons and not one single. I k ow high altitude air is dry...
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A friend of mine set his in tiller hickory bow in a corner.The floor was concrete.After a few months the lower limb was bent more.Seeing is believing.Another friend would set an osage stave that way to dry to induce reflex in the lower limb over time.Then turn it around for the other limb.I'm sure that's been heard of before but now the use of the heat gun is wide spread.Now storing them vertically off the ground does'nt seem to bother much from what I see but don't trust it and store them horizontally.Air movement takes care of it.I quess people will have their quirks about things.I say whatever works do it.
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Wooden floors require moisture barriers for a reason. Fog settles.... Dew settles... Earth is damp. Perhaps it many reasons and not one single. I k ow high altitude air is dry...
Yes, but neither fog nor dew are water vapor.
I guess it depends where this bow storage barrel is. Fog and Dew are more of an outdoor phenomena.