Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on July 30, 2017, 04:42:42 pm
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This is my first sinewed bow. It's the one I asked all the questions about. It's Ocean Spray with one layer of sinew. It's 53" TTT measured straight across and it's 59" TTT following the bends. 45#@26". Shoots in the high 160's. Best was 3 170's @ 10gpp. Birch bark back and a leather handle wrap that looks a little too much like fish net stockings. It's really nice to shoot. After I shoot this for a bit everything else kicks like a mule. Sinewing wasn't too bad but the bark was a little tough. If I'd realised that it would smooth out as the glue dried I might not has fussed so much and would have ended up with a much better job. I would consider this a successful sinew job so as PatM says there will be more in my future. Thanks for all the help everyone.
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Nice looking shooter Don! Cheers- Brendan
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Pretty sweet looking full draw.Good to see you persisted through this one.Glad it shoots good for ya too.
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Nice bend there DC, glad you where successful and looking forward to seeing more
Bjrogg
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Nice bow, DC. The side profile, unbraced, braced and full draw are quite nice. Very well done. :OK
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very nice bow. thanks for posting
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wow very nice,, congrats :OK
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Nice , I bet those big hooks make drawing that baby sweet from brace to FD... ;)
DBar
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Nice looking bow
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Way to go DC!!!!!! That bow looks awesome. Those are some serious hooks and like Pat said the profiles are money. 8) Congrats my friend!
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Nice workmanship. I like the way you did the tips, they came out looking good.
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What's not to love about that!
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Very nice work!
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Great job on that one! I love the bends!
Patrick
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Don great job on that one! Can tell that one took a lot of work
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Killer bow, Don, killer.
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Nice sweet looking bow, I really like those tips great speed to !
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That's what I like right there!
I have yet to back with birch bark. Is there a build along somewhere? It seems kinda stiff and I don't know if theres a way to soften it up or what. Looks great on yours though!
Marco
PS what did you do on the curve underlays and the what are the bridges of?
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Chris stole my line. SUPER killer Don.
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Awesome bow, I really like the hooks and that birch bark job.
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Thanks for all the compliments, I really appreciate it.
Marco, the bridges are just four little triangles of bone CA'd in place. I Googled "Backing a bow with birch bark" and got quite a few hits. One suggests boiling the bark. I tried it on a test piece and it just shrivelled up, so I wouldn't recommend that. I stripped the bark down to the thinnest layer I could and soaked it in warmish water for a half hour or so. It gets a little stretchy when it's wet. Then just glue it on and smooth it out. I wrapped mine with 1" wide sewing elastic, not very tight. Removed the elastic after 15-20 mins. Be careful removing it if you were a little sloppy with the glue. This wrapping part could be improved on because this is where I had my problems. Lifting edges and such. Mine looked very lumpy at first but flattened out as the glue set up. The camera was my friend here because it looks better in pictures than it actually is. But for first try I'll take it.
I just kerfed the tips, steam bent the curves and glued in an insert. I had to kerf them because I haven't had any luck putting tight bends in Ocean Spray.
Again thanks for all the nice remarks
Don
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Those are some serious hooks! Love it! Love the birch bark as well. Have to try that some time
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great job! what a beautiful piece of work... love everything about it
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Perfect! I mean, I know you can see the flaws because you were there when they happened, ...but the rest of us are just overwhelmed by the charm of those gracious curves. I'd love to have a little bow like that for hunting from a blind!
OneBow
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Very nice clean bow,great job on the recurves,braced profile,the sinew job and just a great job all around.
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Great work Don!!
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Great Job on a fine looking bow!!
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I've been waiting to see a sinewed oceanspray, way to go DC! That thing looks sweet.
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I haven't seen one either. I'm hoping it won't chrysal but time will tell.
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That is a good looking bow, well done. If Ocean spray is not prone to chrysalling then it will be even less prone with the sinew.
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<snip> If Ocean spray is not prone to chrysalling then it will be even less prone with the sinew.
PLEASE help me understand this point, because I'm confused. I don't understand how a sinew backing would manage to both increase the draw weight and tension strength of the bow, yet somehow decrease the propensity to form chrysals. ??? My understanding is that a given surface area or volume of wood on the belly of a bow forms chrysals when the compressive force applied against it exceeds the capacity that the wood can bare. It seems to me that adding tension force resistance to the back of the bow and increasing the draw weight of the bow would necessarily increase the compression stress on the belly as the bow is drawn. ...which should deductively increase the propensity to forms chrysals on the belly, - - - I think.
I have been trying to noodle out a way to make the physics work for this, but I keep winding up in the place I started. I went down several different rabbit holes trying to figure this out. I contemplated differential curves of force being applied by sinew vs. wood. I considered the resting brace state vs the momentary full draw load and how it might be different. Materials science is one of my favorite curiosities, but there is MUCH of it that remains mysterious to me. It just seems that if more force is applied to the same belly material, the probability of the fibers in the belly reacting to that force to form chrysals HAS TO be increased! ...but I read frequently that the opposite is the case with sinew as the backing and cannot noodle out why it is so!
I know sinew is magical stuff, but I don't really get how it can do some of the stuff it is said to be capable of. I'm sure I am missing some key little bit of understanding of how it works or the properties of the material, but I just cannot wrap my cerebellum around it yet. Can anybody help me understand?
OneBow
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<snip> If Ocean spray is not prone to chrysalling then it will be even less prone with the sinew.
PLEASE help me understand this point, because I'm confused. I don't understand how a sinew backing would manage to both increase the draw weight and tension strength of the bow, yet somehow decrease the propensity to form chrysals. ??? My understanding is that a given surface area or volume of wood on the belly of a bow forms chrysals when the compressive force applied against it exceeds the capacity that the wood can bare. It seems to me that adding tension force resistance to the back of the bow and increasing the draw weight of the bow would necessarily increase the compression stress on the belly as the bow is drawn. ...which should deductively increase the propensity to forms chrysals on the belly, - - - I think.
I have been trying to noodle out a way to make the physics work for this, but I keep winding up in the place I started. I went down several different rabbit holes trying to figure this out. I contemplated differential curves of force being applied by sinew vs. wood. I considered the resting brace state vs the momentary full draw load and how it might be different. Materials science is one of my favorite curiosities, but there is MUCH of it that remains mysterious to me. It just seems that if more force is applied to the same belly material, the probability of the fibers in the belly reacting to that force to form chrysals HAS TO be increased! ...but I read frequently that the opposite is the case with sinew as the backing and cannot noodle out why it is so!
I know sinew is magical stuff, but I don't really get how it can do some of the stuff it is said to be capable of. I'm sure I am missing some key little bit of understanding of how it works or the properties of the material, but I just cannot wrap my cerebellum around it yet. Can anybody help me understand?
OneBow
You are confused because of the idea that sinew adds tensions strength, it does not. The magic of sinew is its elasticity. Wood is somewhat stronger in compression than sinew is in tension so having a sinew backing allows the back to work more thereby reducing stress on the belly
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I'm sure I am missing some key little bit of understanding
adding sinew to a limb will make it stiffer, assuming of course that the wood that it is added to, does not get thinned.
adding sinew and retillering (thinning) the belly wood , makes a different limb, as Mark has described.
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You are confused because of the idea that sinew adds tensions strength, it does not. The magic of sinew is its elasticity. Wood is somewhat stronger in compression than sinew is in tension so having a sinew backing allows the back to work more thereby reducing stress on the belly
OK - I'm still confused. I guess I think of a bow as a balanced system. The belly and the back have equal and opposite forces acting upon them as the bow bends. I.E. - A fifty pound draw weight bow when drawn has 50 pounds of tension strain on the back spread over whatever the surface area/volume of the back is and 50 pounds of compression force working against whatever the surface area/volume of the belly is. Now both the back and the belly may have a greater degree of 'capacity' for tension or compression force resistance, but when the bow is drawn to 50 pounds of draw weight, neither the back nor the belly is holding more or less than 50 pounds, regardless of it's capacity. Similarly, if the new backing of sinew is going to increase the draw weight of the bow, say to 65 pounds, then both the backing AND the belly are going to be subjected to 65 pounds of strain, the back in tension and the belly in compression. I just cannot sort out how the 'elasticity' of the sinew on the back is going to relieve the compression force that has to be endured by the belly.
OneBow
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]OK - I'm still confused. I guess I think of a bow as a balanced system.
OneBow[/color][/size][/font]
Is it? What about the neutral plane position?
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ok maybe I am over simplifiing ,, but the sinew stretches more than wood,, so does not but the same compression force on the belly,, as a wood back does,,,, am I close,,???? (SH)
ok for example, when u put on a bamboo backing that is too thick it will crush the belly,,cause its too strong,
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ok maybe I am over simplifiing ,, but the sinew stretches more than wood,, so does not but the same compression force on the belly,, as a wood back does,,,, am I close,,???? (SH)
ok for example, when u put on a bamboo backing that is too thick it will crush the belly,,cause its too strong,
I'm like Eric. I don't understand how you can have more tension and poundage without out requiring more compression to counteract it.
I can understand how a sinew bow of same weight as all wood bow could be faster because of the elasticity of the sinew.
I'm not saying it's not true, I like Eric just can't seem to comprehend how this works. I like to figure out how things work. In my mind it seems it would be like the thick bamboo and overpower the belly. Must be something I'm missing. Don't mean to get off track on this post DC. I think you post a comparable question once that went on for 12 or more pages.
Nice bow D.C., I really do need to try sinew. I shot Paulsemp's at Elm Hall and was very impressed. For its physical size and weight it was a very nice shooting bow.
Bjrogg
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And even after 12 pages I'm not sure how it works but it does ;D ;D
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ok maybe I am over simplifiing ,, but the sinew stretches more than wood,, so does not but the same compression force on the belly,, as a wood back does,,,, am I close,,???? (SH)
ok for example, when u put on a bamboo backing that is too thick it will crush the belly,,cause its too strong,
I'm like Eric. I don't understand how you can have more tension and poundage without out requiring more compression to counteract it.
I can understand how a sinew bow of same weight as all wood bow could be faster because of the elasticity of the sinew.
I'm not saying it's not true, I like Eric just can't seem to comprehend how this works. I like to figure out how things work. In my mind it seems it would be like the thick bamboo and overpower the belly. Must be something I'm missing. Don't mean to get off track on this post DC. I think you post a comparable question once that went on for 12 or more pages.
Nice bow D.C., I really do need to try sinew. I shot Paulsemp's at Elm Hall and was very impressed. For its physical size and weight it was a very nice shooting bow.
Bjrogg
Because the belly is not storing more energy, it's the back/sinew.
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Because the belly is not storing more energy, it's the back/sinew.
...Mark - We should perhaps move this to a new thread, but how does the sinew on the back 'store more energy' without increasing the resistance force required of the belly? How can you increase the draw force on the tension side of the bow, without similarly increasing the compression force pushed against the belly?
OneBow
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I don't mind if it's here, just don't move it to PM's. I'm hoping to learn something.
Does the added thickness make much difference?
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I've read that bow building will drive accountants crazy.
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because the sinew is stretchy and magic,, (-P
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If DC doesn't mind the side discussion, I will try to offer an explanation. One source of confusion in these kind of discussions is the different ways folks often use the same word to mean different things.
The term strain is usually understood in science as a linear measurement. For example, if a rubber band 12" long is stretched to 13", by hanging a weight on it, then the strain is said to be.... 1 inch per foot.
I hope Onebow does not mind me reforming his statement to what I think he meant.
then both the backing AND the belly are going to be subjected to 65 pounds of strain force, the back in tension and the belly in compression
With a given force, how much the sinew or wood stretches on the back of the bow depends on its "stiffness",and how much it can stretch before it breaks, is its elasticity.
Sinew of course is not as stiff as wood so it wants to stretch more than a wood back, and does so without breaking, because it can. The tension and compression forces on the back and belly are still equal.
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(-P
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You have to account for the properties of the wood as well. Sinew is essentially all equal. Wood is not.
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By adding an elastic backing to the bow then the belly will not endure as much compression force. Essentially what is happening is the neutral plane has shifted towards the belly of the limbs making for more stretch on the back and less compressing of the belly
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Think about it like this, the belly is under about the same amount of strain as it would be under if the bow weight was measured without the sinew. By adding the sinew you up the draw weight without really adding much strain to the belly because the sinew is stretching.
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One thing that confuses me is that you can bend a sinewed bow so much farther. Do you think that a selfbow would bend that far if the back would hold out?
Another thought is that for a sinewed and unsinewed bow of the same weight the wood on the sinewed one will likely be thinner so it will bend farther.
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OK - Sorry it took so long, ...but I think I am seeing my way through this little puzzle a bit. It helped me to realize that the Compression vs. Tension ratio was still balanced and how that could be explained by the elasticity of the sinew. Basically, the sinew on the back of the bow is not starting at zero. Rather, it is starting from a negative value for it's compression force of 5 - 15 pounds of draw weight due to it's elastic properties. Before the compression force on the belly is loaded up at all, the tension side has already contributed a few pounds of draw weight. I realize that is mental rambling, but I can kinda make sense of it as long as I don't stare at it too long!
Thanx for all of the help...
OneBow
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I've read that bow building will drive accountants crazy.
That's funny Ed. I'm not a accountant but I do like to understand how things work.
I'm wondering, because of its elasticity is the sinew " opposing compression force" being transferred to the original back of the bow instead of the belly? I could understand how this might work. The original back would have less tension force therefore the belly would have less compression force.
I also was thinking like DC in that with all that extra bend, if all the compression force was transferred to the belly like a plain selfbow it would seem to add more stress on belly
Bjrogg
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That thing is awesome dc!
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It was a tough build DC on account of the wood and it's shape.Not many options were left for corrections with heat to get the bow in line besides cold hand twisting and the string to correct and settle it in the way I see it.
They are'nt a lying when they say it takes twice the time to make these type bows compared to self bows,but everyone ought to try it at least once and determine if it's worth it.It can get easier but seems there is always just a slight bit of alignment that needs to be done.Sometimes not.
The farther back the recurve & reflex in the limbs the more finicky it gets.That's why grabbing an almost perfect piece of wood or making it almost perfect before recurves are put on it for these type bows makes the least trouble.
Kuddos for sticking it out DC.You took the rough road on this one for success.Glad it shoots so well for ya.
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Thanks Ed Here's a bit of what I went through. I had to bend it a bit to get the string in line. I didn't want to heat the limbs any more than I had so I heated the handle. I wrapped it with tin foil and opened up the belly side of the foil. I clamped the foil to the sides of the handle and folded it out to keep the heat from going around the back. I opened the drawer and put a hair dryer in there blowing cold air on the back to try to keep it cool. Then I aimed the heat gun at the handle. It worked. I got enough bend. What, me worry ;D ;D Rube Goldberg's got nuthin' on me
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I see.Thanks for posting.Glad it worked.
Having some character on them makes them even more special.
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Extra points for creativity of tool usage DC! )P( )P( )P( - OneBow