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Main Boards => The Bowyer's Bench => Topic started by: George Elkstalker on February 18, 2009, 09:05:00 AM
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Just finished my new bow. Made of ash, backed with sinew. During tillering process it started to follow the string. Started with a very good piece of wood with natural reflex. I had read that the sinew should actually help keep the string follow from happening. Unstrung it now rests probably 4" closer to the string than it did before tillering. Is it too late to heat the limbs, clamp it to a board and try to straighten it?
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String follow, or set, is caused by the wood cells on the belly of the bow collapsing do to stress. The amount of damage will determine if it can be overcome. Adding sinew or other backings will not prevent set if the belly gets undue stress...and sometimes can cause more.
I have successfully eliminated some set in selfbows by heat treating(tempering) the belly of bows but you will get better results by tempering before you stress the wood. Once the damage is done, the damage is done!
If it were me, I'd start another bow and be a bit more careful as I educate the wood. Lots of exercise between wood removal sessions, not taking the bow beyond it's ultimate draw weight or draw length, especially while tillering and not getting rushed or aggravated. Be thoughtful with each wood removal and think ahead of what you are doing but get there when you should and not when you want to.
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String follow, or set, is caused by the wood cells on the belly of the bow collapsing do to stress. The amount of damage will determine if it can be overcome. Adding sinew or other backings will not prevent set if the belly gets undue stress...and sometimes can cause more.
agreed. once the damage is done, it's done. Learn form this one and go make another bow. :)
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Pat stated:
"Adding sinew or other backings will not prevent set if the belly gets undue stress...and sometimes can cause more."
I would think that the sinew may have overpowered the belly of the bow causing more compression to the wood fibers there. Not knowing the design you used and the amount of sinew on the back it is a hard call but that could be it. Ash is a pretty wood and can make a good bow but I don't believe it has the compression strength of many of the other bow woods.
To belly toast the bow now would probably ruin the sinew backing as it will heat up the glue and cause it to give. Or you can remove the sinew and toast the belly.
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There all right above.Once it's there.Chalk it up to exspeirence.Start a new bow,any string follow isn't wanted but an inch or two,not all that bad in selfbows.It's said it may even help some bows or shooters.After two inchs you start to lose a alot of cast,arrow speed.
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There all right above.Once it's there.Chalk it up to exspeirence.Start a new bow,any string follow isn't wanted but an inch or two,not all that bad in selfbows.It's said it may even help some bows or shooters.After two inchs you start to lose a alot of cast,arrow speed.
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How much do you exercise a bow between wood shavings? Didn't know I was supposed to. I never bent it far at all until I had good tiller at around brace height. Please explain exercise in full. Thanks!
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Tillering takes time to get just right with many trips from the work bench scraping off belly limb wood to the tillering tree. Every time you peal off 10 or 20 curls of belly wood and go over to the tillering tree you will want to flex the limbs 20 to 50 times to give the wood a chance to learn to bend at that level.
Say you want a 50 lbs. bow at 28 inches and it is currently pulling 45 lbs. at 10 inches. You will go back to scraping wood. Once you think you've taken off a goodly bit you return to the tillering tree, if you have one, but you don't want to yank that bow very far at all. Some exersise the limbs before checking draw weight and draw length. I first check the new draw weight and how far the limbs are now pulling. This helps me keep from pulling too far. I personally don't want to pull much more than 45lbs for a 50 lbs bow at this stage. So you pull 45 lbs at 12 inches now. Good, you just progress toward your goal 2 inches. Now pull the bow back no more than that 12" mark 20 to 50 times to work the bow to it's new configuration. That is exersising the limbs. Then go back to the work bench, make new shavings, and start the process all over again until you reach your desired draw length and weight. This helps to prevent set in the tillering stage.
Remember once you are an inch from your intended draw weight stop and proceed with your final sanding and rounding of the limb edges. It may then be just where you want it to be.
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I'm sorry for the trouble with your project. That hurts... At the same time, I have to say that having just gone to great lengths to get a form built and lay up a bow to specifically put string follow into that bow, your thread title sure grabbed my attention! Of course with laminated bows, it's a totally different issue, but still, an attention grabber. Good luck with the next project. I've still not worked up to trying a selfbow.
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Thanks again guys for the advice. The book I read before starting didn't say anything about the exercising process. Guess it wasn't as good a book as I thought. Nvertheless I will be making more bows. This is too much fun!!!!!
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Tell us about the design of your bow and your draw length. Is this is a stave you cut? Was the wood wet? Jawge
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ChristopherO, thanks, that is a great way to describe the process of exercising the limbs. Doing it before and after checking the results of scraping, isn't discussed in many places. there is usually just a line telling the bowyer to "exercise the limbs", without the how.
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Does anyone have a picture of a "tillering tree"?
Thanks,
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This is mine.....
(http://i5.photobucket.com/albums/y199/PatBNC/forDon001-1.jpg)
(http://i5.photobucket.com/albums/y199/PatBNC/forDon002-1.jpg)
(http://i5.photobucket.com/albums/y199/PatBNC/forDon006.jpg)
(http://i5.photobucket.com/albums/y199/PatBNC/forDon008.jpg)
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Thanks Pat. Where does the scale come in to play?
Thanks again,
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Also forgot to ask, with such a long rope how does one tell how far the bow is drawn?
Thanks again,
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I hang the scale from the string and attach the rope("S" hook) to the scale.
When using a long string you have to go by tip movement. When I get the bow to bend well with about 8" of tip movement, I know it is time for a short string and a 4" brace height.
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Thanks again Pat.
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Hey Pat B, what are those Doodads sticking out the side of your tillering tree?
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One is a pencil for marking flat spots and possible hinges. The other is a small screw driver for zeroing the scale when I hang it on the string. Just above them is a screw that I hang the clip from the tiller rope.
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Going to throw in my 2 cents worth here. Never draw the bow past the desired weight. It doesn't matter if there is a long tillering string or a short brace height string on the bow. That is what the scale is used for. Start "sweating" the bow as soon as it can be bent evenly on both limbs. Pull the bow close to desired weight. Mark on the tillering board where that weight is with a piece of masking tape. Then pull 100 times to that mark. Retest the weight with the scale. If the limbs are still bending evenly and the weight has changed, mark where the new length at desired draw weight is and draw another 100 times. When the draw weight stops changing after 100 pulls is the time to take more wood off. I have done this with many bows of different woods over the past 3 years and have seen string follow reduced dramatically.
That being said, I am not convinced that string follow is a bad thing. The mulberry bow I made spring of 2008 has shot well over a thousand arrows, killed numerous big game animals, has almost 3" of string follow and shoots just as hard if not harder than many I have made without string follow. Go figure.
Sure have enjoyed being a "lurker" up until now.
Jim "jimmy the sammi"
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Welcome Jim. Looking forward to more of your input.
I usually don't pull my bows as much as you do after each wood removal but I do pull 20 to 30 times...and never over ultimate draw weight or length. What I do is after low brace height has been achieved I will let the bow rest at low brace for at least an hour at first and gradually longer and higher as tillering progresses until I hit the ultimate brace height(for me 5 1/2" to 6"; my fistmele). I believe we are achieving the same goal but with different routes. That's what I find so interesting about wood bow building. There is more than one way to skin a cat (as we used to say as kids).
String follow is only bad if you are trying to get every bit of energy from a bow. If your goal is an effective, smooth shooting bow, string follow(within limits) doesn't matter. If you are trying to achieve zero string follow, wood bows are not for you. Wood is organic and as wood is stressed the cells on the belly side compress and on the back side stretch. You can not prevent this with wood bows but you can limit it. It is the nature of the wood. You can minimize string follow with proper tillering practices and patience. Even if you add 2" of backset and you end up with either a flat profile or slight reflex, you still have string follow, the cells have been compressed or stretched, it just isn't as apparent in the unbraced profile.