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Main Boards => The Bowyer's Bench => Topic started by: Leo L. on April 16, 2009, 10:29:00 AM
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Say you left your bow strung, and it took on some string follow. Since the bow is finished, can the bow be put onto a form and heated to apply some back set? Would the finish have to be taken off?
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Be careful. I took a yew english bow off the tiller tree. And decided to turn over and push on the back a tad to remove follow frem being on teh tiller stick and she blew up on me.
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:eek: :eek:
Not good!
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I am not sure, made a learning mistake on my first bow that caused the limbs to be real narrow, by the time I got to tillerin' it I could see that I would have string follow in it, and was wondering the same thing. I figured that since I had already started teachin' the limbs to bend, heating it and making it go the other way would be a sure receipe for disaster. The bow came out a bit heavier than expected, shoots great, and I learned a ton getting it done. Time to start a new one!!!!
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You can get most out with a heat gun-like the one for scraping paint-how long will it stay out? Who knows.
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Set is caused by crushing belly wood. Assuming the wood was dry, it's probably permanent. Sometimes wood that is crushed when wet can be brought back some. You can certainly heat it and get some backset into it but the damage is still there and it will probably go right back.
Think about it like this. You have 2 planes (or layers) that do the work in a bow.
The back stretches during the draw and then returns to it's previous state depending on how elastic it is. Once the wood is stretched beyond its ability to stretch, damage occurs and the wood can pretty much never be the same. This isn't too common in most woods because they are almost all stronger in tension (stretching) than they are in compression.
The belly compresses and then returns to its previous position depending on how resistant it is to crushing. Once the wood is crushed, damage occurs and the wood can pretty much never be the same.
There are exceptions and some heat treating, depending on how hot and plastic you can get the cells, can help.
How much set are we talkin' here?
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Brad Smith had a thread over on the Wall that touched on this subject.......but with a different twist. He took a friend's bow that had to much set in it and cut the handle out using a fishtail splice and then he glued 'er back together with the desired backset. Very simple.
ART B
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I have a Osage bow that I toasted the belly and while it was hot I put it clamped flat on a 2x4 and let it cool. It has worked so far but you have to let it rehydrate for at least a week, putting in the bathroom would help. It also added about 5 or 6 pounds.
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Once the belly is crushed it is permanent. The only way to "fix" it is to remove the damaged belly wood which, of course, will cause your bow to loose weight. Adding more backset will stress the belly more and likely reduce the efficiency of the limbs. I've not had much luck using heat to correct set - the effect is temporary and the limbs will eventually return to their pre-treated state.
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String it backwards, heat treat, whatever-- the effect is temperoary. Crushed cells, are like broken eggs-- you can't put them back to------again. I think bending back and forth, can have the similar effect bending a piece of wire back and forth.--it weakens it further. Live w/ what you have, some string follow is not necessarily a bad thing. Or as gordonf says,remove damaged belly wood-- If bow is too light to your liking,after this - Pass it along to someone who would like it -- and enjoy building the next one--a bit wiser. Ive found it is actually more fun to watch someone enjoy a bow that you have made, than to shoot them yourself,- even the ones that do suit you. Just another way to enjoy these home built bows.
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My situation was a hypothetical, and hasn't actually happened to me....yet. Not saying it won't either. I am working on my first Osage stave, and not even near floor tillering yet. I was just sitting here, reading the threads, and some other internet resources and started pondering...WHAT IF that happened. Could it be undone?
I actually found the answer to my question earlier today while reading "The Bent Stick" by Paul Comstock. I can post an excerpt from the book tomorrow as I left it at work, but basically what he said that you should never try to induce a backset on a stave that doesn't already have it, simply because the back was meant to expand and the belly to compress (exactly what John Scifres was saying).
After reading a good portion of Paul's book today, I've got a pretty good understanding of how this stuff works now.
My stave...it's got some natural backset on one end.
(http://img.photobucket.com/albums/v338/uscg4good/DSC04790.jpg)
(http://img.photobucket.com/albums/v338/uscg4good/DSC04793.jpg)
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Leo,
Being in S.La (high humidity) you really need to build a drybox and get a humidity meter. Once you get that bow to the floor tillering stage keep it in the dry box.
I made probably a dozen very average bows until I started using a dry box and the difference was dramatic...less set, faster, etc.
There is just no way to naturally dry wood in our climate.
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but basically what he said that you should never try to induce a backset on a stave that doesn't already have it, simply because the back was meant to expand and the belly to compress
I agree if the wood has taken a set due to poor tillering, compression, etc. but on a piece of wood in the floor-tillering stage I pretty much always use a caul and heat-gun to induce some reflex.
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In my post I forgot the mention that after it rehydrate I scraped the 5#'s off and maybe that helped.
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Here's that excerpt I mentioned earlier...
(http://images.imagelinky.com/1239976724.JPG)
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Most of what I learned about making bows and wood was from guys like Paul. I'm mostly a parrot with a bunch of practical experience in not listening. We learn by doing, and in my case screwing up :)
Brad's ideas are very valid. There are other ways of making a set bow better. Removing crushed wood and shifting the planes is the best because you are starting with fresh wood. You can bring weight back up by adding something like sinew to do the tension work.
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I've had a little success mitigating set by adding some reflex to areas that don't bend. Good candidates are the handle area by adding some set back and reflexing the last 8 inches or so. Keep the wood dry, tiller well and never pull the stave beyond what it takes to expose a problem. Jawge
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Leo,
Been awhile since I've read "The Bent Stick"...I know I used the heck out of it when I first started making bows.
I'm not gonna be so bold as to disagree with Paul Comstock, but I will say that I could take Stave B in the picture you posted above, use a heat-gun/caul to give is some reflex and make a nice bow that wouldn't follow the string any more than Stave A.
You'll probably want to straighten the piece of wood you've got so you might as well put some reflex in the other end while you are at it.
I would avoid Stave C unless it was the only wood I had.
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When a bow develops set/string follow, caused by damage to the belly, how deep does this plane go. What I want to know is does the dqamage only occur in the immediate layer of wood, a 1/16th" deep, an 1/8th" deep etc. I know it will be different from bow to bow, but does anybody have an idea.
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Mike, thanks for the tip. I'll probably end up doing just that. This is the stave you gave me last June at the Primitive Expo. Yea I'm still chasing that ring, it's whooping my butt. I've been using scissors mostly to scrape, and a scraper set as well. That draw knife there was too sharp and was splintering the wood. I want to finish this bow by season opener.
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That is a tough piece of wood for your fist bow...wish I would have had something better for you.
I think I've got some good billets but it has been years since I cut them and they may not be as "good" as I remember. I'll try to get some read before the primitive expo.
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I have an osage selfbow that I built back in the mid '90s that I have mentioned here in a topic about wanting to know how to reduce the draw weight on. Some of you may remember it. I hope to soon be starting on the weight reduction by following the great advice I got from you guys. So, since the bow is very heavy in draw weight, and it has about an inch and a half to two inches of string follow, do I take out some of the set in it AFTER I remove some of the belly wood? Or, do I try to induce reflex into it BEFORE I remove belly wood?
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Razorback,
I would say the most damaged fibers are concentrated in the first few 16ths of the belly. Take about 10 pounds off the bow. Then sinew it to bring it back up to weight. The sinew is probably making the most of the correction but you are certainly gaining some compression strength back by shifting the planes a bit.
ishootforthrills, take belly wood off to reduce weight. Then you can heat bend to induce some reflex. It should be a better bow.
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Upon reading Mark Saint Louis' chapter in the last TTBB I get the impression he heat treats an older bow before he retillers and adjust weight. His example was of a bow that took too much set. He toasted the belly well, which increased draw weight while inducing refex, then scraped it down to original weight. His result was a bow without the string follow and with much more arrow cast.
There has been a lot learned about bow making since Mr. Compstock's writings. Not to take anything away from his expertise but it has been said he has changed his views on some of his dogma since that was first published.
From personal experience, though, heat treating does a wonderful thing to a piece of wood but too much compression strength will over power even osage in tension. I noticed just yesterday that a sweet little osage bow I am finishing up has developed a splinter in the back due to too much relex for the stave. I originally induced nearly 4" and it has kept 1/2 of that but it won't last long unless I cover that area with rawhide.
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My experience is that once it takes set, that's it. Heat correction remedies look great initially off the form, the after drawing the bow back a few times, the set returns.
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Instead of heat treating an older bow that took too much set, take the experiences learned from that and other bows and put that positive energy towards building a more successful bow. I have used heat treating(tempering) to reduce set and/or increase compression strength in bows that took too much set and it works to some extent. You would be better served by heat treating and adding a limited amount of backset(reflex) to a bow being built so not to damage the belly cells to begin with. Adding too much reflex can also cause excessive compression stress in a bow being built so you end up with the same situation as you did with a bow with too much set. By adding 2" to 3" of backset and tempering the belly(primarily with whitewoods) as you straighten(laterally) your stave you can achieve a bow with 1" of reflex or a flat profile that will maintain it's shape for the rest of it's life, which can be many thousands of shots.
I have used tempering on osage with good results but generally osage is compressing strong enough without it. If you take your time while building a wood bow, don't over stress the wood, don't pull it beyond its ultimate draw weight of length and exercise the limbs with each wood removal you can build a wood with a limited amount of set. Instead of putting your energy into trying to fix a bow with too much set, figure out why it has too much set and work towards eliminating or minimalizing the stresses that caused that set to begin with. Over stressing bow wood is the main cause of set and I am still guilty of doing this after building hundreds of bows over the last 25 or so years. If your mind and concentration aren't into the building process, put down the tools and walk away until you can concentrate on a positive bow building processes.