Primitive Archer
Main Discussion Area => Bows => Topic started by: coaster500 on June 09, 2012, 03:44:57 pm
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I've got a take down that I built that comes in about 41#s. It shoots very well but I was thinking about sinew to add a bit of weight. I could pike it a little but it is at 62"s now and I like the length.
Will sinew help with a 62" bow and how much weight would two or three layers of sinew add?
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The longer the bow, the less result you get from the sinew. You have to "load" the sinew to a certain point to overcome the weight it adds to the limbs. On longer bows your arc on the limbs is less than on shorter bows, the return on investment is just not there. How long is the draw length? Stiff handle or bendy handle?
You might need to pike an inch off each limb and add sinew to boot if you are looking for 50#'s of draw. One really good layer on the whole bow (if you are good at laying up sinew) and another right down the middle of the limbs would give you a good 5-6 lbs, plus what the piking adds.
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So how much would you pike it to get the most from the sinew? Is there any benefit to flipping the tips for the sinew or should I leave them straight?
sorry the draw length is 28"s for this bow...
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I believe it to be a perfect canidate for sinew. I would leave the bow as is and put 5" blocks under each tip. Tie the center down and add 2-3 layers of sinew. It will add well over 10# and give you a chance to scrape some compressed fibers away and start virtually fresh. The take down part is the tough part. That sinew matrix works together all across the length of the bow. Stopping it midway will negate some of the bonus, but still serve its purpose.
Side note: Flipping tip adds at least 3-6#'s.
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It is hard to say. Depends on the bow, wood and design,and your local RH. You could get about
10# with 2 to 3 layers.
Other options would be to kick the tips up a bit and tempering the belly.
Ideally 2x your draw length would give you a good bow length for sinew.
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I just realized I don't know what wood you used. Osage?
If you got osage, you could pike it down to double your draw length and lay on the sinew. My every-day-shooter is 52" nock to nock and I pull 26".
With the 28" draw, 59-60" of bow would get decent reaction with the sinew. The back of the bow would really start to resist tension and cause the plane of neutrality to move closer to the back. You would, in effect, have more belly wood resisting compression causing the limbs to store more energy.
But that's just my take on things. Don't grab the saw just yet, let's get a few others to weigh in on the subject.
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The bow is Osage made from matching billits.. it is finished with tru oil with a flat spar finish. How would you remove this finish from the back of the bow?
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The amount of reflex is every bit as important as the length is. A short bow with follow still wont work the sinew as hard as a longer bow with ample reflex will. I have a 64" ttt sinewd osage flatbow with 2" of solid relfex at it shoots great. Im quite sure the sinew is working hard even at 64" ttt. Like J-dub, this is just my spin on it. None of us have done much lab testing!
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Easy does it scraper work is how I remove sealer Kip. You will see the white curls turn to yellow, stop there and finish with sandpaper.
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Thanks guys I'll get at it next week :)
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How is the fact that it is a take down bow going to affect the sinew backing? Won't you have to stop the sinew in the fades? I'm just having a hard time picturing this in my head at the moment.
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I've tried a couple times to add draw weight with sinew and wasn't very successful either time. On the other hand bows I've designed from the start to be short, stressed and sinew backed are great. My honest opinion is that piking, flipping and heat treating will serve you better. I will defer to Pearlie on adding reflex. I hate to tiller big reflex so I never do it. Perhaps had I done that things would have been better on my fix it attempts. However, my rule is that I only use sinew if I'm planning on it from the outset.
Good luck with the bow.
George
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How is the fact that it is a take down bow going to affect the sinew backing? Won't you have to stop the sinew in the fades? I'm just having a hard time picturing this in my head at the moment.
Clint I mesh my entire bow together when I sinew them. My first piece is right dead center with equal portions each side of center. Then continure on with that pattern. The whole bow worth of sinew is working as one. The two piece bow wont allow that.
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So Coaster500 won't be able to add sinew to his bow?
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Sure he can. I just prefer to tie it all together. Sinew can still work split at the middle.
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The first couple of sinew backed bows I built I only put sinew on working portions of the limbs, not the tips or the handle. They all took set in the handle area. I think it is important to make the sinew backing "matt" all one piece through the bow, limbs and handle. The tips on the other hand I don't think need sinew and it will only add extra physical weight to the tips without any performance advantage.
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I wrote an article in a German magazine about 15 years ago about sinew backing.
In the article I stated, "I disagree with backing a bow with sinew as a remedy for a poorly built bow." (Not to say Coaster, that yours is poorly built.) If I wrote it today, I would add, "for a bow that turned out light."
I also went on to say, "Backing a bow with sinew should be intentional. It should be done for the purpose of building a special bow with unique requirements. A considerably shorter bow that still allows the same draw length and weight of its all wooden counterpart."
I've sinewed a bunch of bows since then and still agree with my statement of yesterday. Again, not that yours is poorly built. More times than not, the "fix" doesn't turn out as you hoped. Sinewing should be part of the plan from the very beginning. What I'm trying to say is, be happy with the bow you just made and chalk it up to experience and learning. To this day, I make bows that come out lighter than I wished for. :-[ >:( It happens. If you just can't stand it, do what I do...give it to a kid. ;D
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This is interesting and I may do it just to find out how it works with the takedown. I've got enough sinew prepared to do this bow and the Ishi type yew I'm working on (it was planned for sinew).... just thought it would be cool to add a bit of weight to the takedown as I did miss the weight a bit.
You guys have got me thinking :)
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Here is what I would do.
Cut to 60 ntn.
Recurve the tips, short and sharp recurves.
Heat treat it into as much reflex as you dare :o osage can take a lot.
Crown the back if it's flattish now. Even it if fairly crowned then excentuate the curve by rounding the edges.
Sinew it. You want the finished back to be nicely crowned. With most of the sinew running down the center - this way you save on weight and get the most out of it.
Then have fun trying to string it for the first time >:D
A while ago I did this process to on osage bow I made before I understood the materials properly and got quite a few extra fps out of it.
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http://www.primitivearcher.com/smf/index.php/topic,29960.15.html
This is the bow and i'm just off to a 3d comp shooting it :)
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I totally agree with Matt's thinking and writings. This should go for any bow building process. If you want a selfbow, build a selfbow. If it comes in under weight or whatever, mark it up for experience and make another using that experience. This is how we learn.
After my experiences with not having the sinew backing one continuous layer through the handle I am curious how using a take down system will affect the overall performance of the sinew. Can each limb be isolated from the other and still give max performance that is expected from a sinew backed bow?
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Its a curious thought for sure Pat. I think it could as long as the handle area was wrapped and secured well so the limb stayed "loaded" when the two halves are seperated. I would like to see a few built and see what happens. Its really so hard to measure and know with all natural stuff. It just varies too much. Suppose thats why we all agree to disagree so friendly like huh?